Books : Permit-Required Confined Space (PRCS) : Section III: Controls

SECTION III: CONTROLS

Atmospheric Monitoring Equipment & General Testing Protocol

Dangerous concentrations of gases and vapors may exist in a confined space and these hazards cannot be seen and may not be smelled. Therefore, air monitoring equipment is necessary to properly test the space prior to entry.

There are two (2) major types of direct reading atmospheric testing equipment used, electronic gas detectors and gas detector tubes. Direct reading instruments are portable units which can be carried in hand or worn on a belt. These devices may be subject to cross‑sensitivity, which means that more than one chemical can give the same or similar response. Interfering chemicals may give a positive or negative deflection from the true atmospheric concentrations. Other factors, which are discussed later in this section, may have a direct influence on the proper use and reliability of this equipment. Therefore, it is very important that the individual performing the tests be properly trained on the actual use, maintenance, limitations, and proper selection of the appropriate instrument.

Electrical Gas Detection Monitors

Electrical gas detection instruments are battery‑powered, direct‑reading devices capable of providing continuous monitoring of a permit space. Oxygen monitors measure atmospheric concentrations generally over a range of 0 to 25 percent oxygen in air.

Combustible gas monitors display concentrations in percent of the LEL, some in percent by volume, and others display both. However, most combustible gas monitors display concentrations in percent of the LEL. Instruments that measure in the percent of the LEL are generally easier to use. For example, the LEL of methane is 5 percent by volume and the UEL is 15 percent by volume. When the concentration in a space reaches 2.5 percent by volume, it is 50 percent of the LEL. When the concentration reaches 5 percent by volume, it is 100 percent of the LEL.

Toxic gas monitors use specific electrochemical cells to measure substances such as carbon monoxide, hydrogen sulfide, chlorine, ammonia or other toxic gases of interest. The instruments are direct reading, available with either meters or digital read‑outs and may also be equipped with alarms. Some instruments are equipped with a single sensor while others have multiple sensors to simultaneously measure a variety of gases. These devices are commonly referred to as 2‑in‑1, 3‑in1, 4‑in‑1 monitors.

It is very important to select the instrument for the specific applications(s) to be encountered. Therefore, whenever specific contaminants have been identified, substance specific detectors should be used.

Special consideration must also be given to the use and interpretation of the results obtained from electrical gas meters under certain circumstances. The operator must be aware of situations which could interfere with the collection of accurate monitoring data. Instrument familiarization by the operator is needed for accurate atmospheric testing. A thorough understanding of the manufacturer's written operating instructions is a major component for the safe and effective use of the instrument. Therefore, employees who use this equipment must be trained on these operating instructions and receive hands‑on training as well. The operator should also be aware of the following facts concerning electrical gas monitors:

1) The instrument must be certified intrinsically safe for use in Class1, Division1, Groups A, B, C, and D hazardous locations.

2) Some combustible gas meter sensors are wheatstone bridge type sensors. This type of sensor can be easily poisoned by silicone vapors, leaded gasoline, sulfur compounds, and repeated exposure to halogenated hydrocarbons. This desensitization will cause erroneous low readings and appreciably reduce the life expectancy of the sensor.

3) The instrument selected must be specific to the substances likely to be found.

4) High relative humidity (90‑100%) may cause a reduction in sensitivity and erratic behavior including an inability to properly calibrate the instrument.

5) Sensors have a limited life span, for example, oxygen sensors typically have a one year life span. Exposure to corrosive substances such as acid gases can significantly reduce sensors' life expectancy.

6) Erroneously low‑readings can result from substances condensing in the sampling line or sensors. Substances such as chlorine, hydrogen sulfide, sulfur dioxide, and ammonia are some of the substances which can be absorbed into the sampling line. In drying ovens or unusually hot locations, solvent vapors with high boiling points may condense in the sampling lines.

7) Battery maintenance is very important. There are basically three different types of batteries currently used: nickel cadmium, alkaline, or sealed lead‑acid. Each has advantages and disadvantages which should be researched with the manufacturer at the time of purchase.

8) Make sure the instrument has remote sampling capabilities.

9) Calibration of Electronic Gas Detectors

Gas detectors must be checked and calibrated each day prior to use. The inspection should include checking hoses, batteries, and any pumps the equipment might have. The unit must also be field tested using test gas cylinders containing known amounts of the substance to be encountered.

Oxygen meters should be calibrated in fresh air to 21%. They should also be tested to see if they respond to changes by holding one's breath and then breathing into the sensor. The sensor should drop to approximately 16%.

If the equipment does not calibrate properly, the unit must be removed from service. Replace the sensor or return the unit to the factory for repair and/or laboratory recalibration.

Operators should consult with the manufacturer's instructions or calibration curves when sampling for gases and vapors against which the instrument was not calibrated.

Detector Tubes/Pumps Method

Detector tube pumps are portable instruments which use a variety of detector tubes to measure the concentration of a wide variety of substances. The operating principle consists of drawing a known volume of air through a detector tube designed to measure the concentration of the substance of interest.

Detector tubes are easy to use and provide a relatively good idea of the concentration of a substance within a space. The length of stain or degree of color change corresponds to the relative concentration of the substance tested. The tubes are generally specific for the toxic substance of concern. However, the accuracy can be affected by cross‑sensitivity. Therefore, the results must be interpreted in relation to the substances in the space.

Limitation for detector tubes include:

  • Tubes can not be interchanged with different brands.
  • Tubes may lack specificity; cross-sensitivity with other compounds is possible. Refer to the manufacturer's manual for effects of interfering substances.
  • Detector tubes give only instantaneous results
  • Tubes have a limited shelf-life (approximately 1-2 years). Refrigeration can extend their shelf life. However, tubes exceeding their expiration date should not be used.
  • Accuracy ranges vary with each detector tube
  • Tube accuracy is significantly affected by cold temperatures. In cold temperatures, try to keep the tubes in a pocket close to the body to keep them warm.

Calibrations and Maintenance:

Operators are reminded to consult the manufacturer's instructions for specific procedures for the calibration and maintenance of the instrument.

General recommendations when conducting atmospheric testing:

1) Use only monitoring instruments that have been properly calibrated and maintained and that are intrinsically safe.

2) Only trained operators who are skilled and knowledgeable with the use and limitations of the instrument should do the testing.

3) Check the area around the confined space opening for any hazardous gas or vapor concentrations.

4) Extreme care must be exercised when opening any confined space that may contain an explosive atmosphere. Some spaces may contain an atmosphere too rich to burn. But when opening the space, air entering will quickly change the atmosphere to an explosive one. Sparks from removing the hatch or cover could ignite the space. Therefore, insert the test probe into a vent hole when possible. If the manhole cover or hatch has no vent opening, open the cover just far enough to insert the probe into the space. Spark‑proof tools must be used. If unacceptable levels are obtained, it will be necessary to purge and ventilate the space. All levels and remote areas of the space need to be tested. An extension device should be used for this purpose. If a hazardous atmosphere is detected, avoid having employees lean over the opening or breathe the air coming out of the space.

5) Oxygen content is always tested first. Make sure sufficient oxygen is available to support the use of the combustible gas monitor. A minimum of 16% oxygen is required for the combustible has monitor to function properly. The sampling protocol requires that combustible gas levels in the confined space be checked next. Flammable gases or vapors must not exceed 10% of the lower flammability limit (LFL).

6) Toxic substances are measured next in parts per million (ppm). Again, the equipment used must be specific and sensitive to the substance likely to be found in the space. Never use a standard flammable gas monitor sensor to test for a toxic substance. The results could be deadly as the following example will show.

Percentage of LFL Hydrogen Sulfide PPM
100% 43,000
10% 4,300
5% 2,150
.7% 300 IDLH
.02% 10 PEL

Hydrogen sulfide is a common toxic gas encountered in many permit space locations. Hydrogen sulfide has an LFL of 4.3% or 43,000 ppm. The standard requires maintaining an environment of less than 10% of the LFL to avoid a potential explosion. Hydrogen sulfide also has Permissible Exposure Limit (PEL) of 10 ppm and an Immediate Dangerous to Life and Health (IDLH) concentration of 300 ppm. Say, for example, the LFL is found to be 5%, though the testing indicates no explosive hazard, it does indicate a level of approximately 2,150 ppm which exceeds the PEL and IDLH.

7) Some toxic substances may not respond very well to electrical gas sensors or detector tubes so more specialized test equipment or laboratory analysis may be necessary.

8) Depending on their density, some gases are heavier than air, others lighter, and some gases are nearly the same weight as air. As a result, gases and vapors will stratify within a given confined space. Therefore, the only safe way to test the atmosphere of a confined space is to sample all levels (top, middle, bottom) with properly calibrated equipment. When monitoring for entries involving a descent into atmospheres which may be stratified, the atmospheric envelope should be tested a distance of approximately four feet (1.22 meters) in the direction of travel and to each side. If a sampling probe is used, the entrant's rate of progress should be slowed to accommodate the sampling speed and detector response.

Ventilation

Once a confined space has been determined to contain or potentially contain a hazardous atmosphere, steps must be taken to ventilate the space before personnel are allowed to enter. Ventilation can be accomplished by natural and mechanical means for the general purpose of:

  • Controlling atmospheric contaminants
  • Prevention of fire and explosion hazards
  • Control of heat and humidity

Natural Ventilation

Natural ventilation is performed by removing roof and side covers and allowing natural air currents to remove gases and vapors. Natural ventilation employs wind and thermal convection to dilute any atmospheric hazard. However, the configuration of some confined spaces and the unpredictability of wind currents and thermal effects makes natural ventilation unreliable as a primary control method. When natural ventilation is insufficient to achieve and maintain acceptable atmospheric levels, mechanical ventilation is necessary.

Mechanical Ventilation

Mechanical ventilation typically refers to mechanical dilution ventilation and local exhaust capture ventilation. The applicability of each method is dependent on the type of atmospheric hazard present, whether the hazard is created by the contents in the space, or created by an operation conducted within the space. When alternative procedures are used, mechanical dilution ventilation is prerequisite.

Mechanical Dilution Ventilation

This method uses mechanical means (fans, blowers, etc.) to provide uncontaminated air to a permit space. This control measure places the permit space in a positive pressure atmospheric condition. If the amount of fresh air being supplied to the space is sufficient, the concentrations of toxic and flammable contaminants can be maintained at acceptable levels. The acceptable dilution ventilation method commonly used is to supply clean air by explosion‑proof blowers located far enough away from any source of contamination.

Air should be blown into a space, which contains a hazardous atmosphere. Remember that contaminants are likely heavier or lighter than air. Blowing air into a space will agitate and help evaporate the contaminants and disperse them throughout the space. A space under positive pressure will eventually expel the contaminant through any openings in the space. Theoretically, air blows a distance of 30 diameter times farther than it can be exhausted.

If an actual or potential hazardous atmosphere exists, then purging of the space is necessary. Keep in mind that forced air ventilation must be directed to ventilate the immediate area where an employee will be or is working. However, during the initial pre‑entry ventilation procedure, the blowing duct outlet should be positioned for uniform dilution and elimination of any gas pockets as illustrated. Shown below are examples of complete and incomplete ventilation of manholes:

When purging a space, an effective initial purging duration must be determined. The following is a list of instructions for determining purging times using the nomographs (line charts) provided.

Instructions

1) Test the confined space atmosphere to determine the initial atmospheric conditions.

2) Use the alignment chart to determine the minimum purging time required by:

a) placing the straight edge on the Confined Space Volume (left scale);

b) placing the other end of the straight edge on the Blower Capacity (right scale);

c) read the minimum required purging time from the diagonal scale in minutes

d) if two blowers are used, add the two capacities and then proceed as outlined above.

3) Note, the effective blower capacity is affected by the number of bends and length of the hose. As the length of hose and the number of bends increases, the effective blower capacity will decrease. The effective blower capacities listed in the alignment charts are based on one to two 90 degree bends and standard 15‑foot blower hose.

4) It is very important to remember that these values are theoretical approximations with safety margins included. The duration for purging a space is dictated by not only the size and blower capacity, but also by the configuration, number of openings and the airborne contaminant. The configuration of some confined spaces, for example multi‑floor‑level spaces or baffled spaces, restrict air flow and require additional purging time. In some situations, adequate purging and venting can only be achieved through permanently installed ventilation ducts that will introduce fresh air directly into the space. In light of this, employers are encouraged to install permanent ventilation ducts whenever possible. Examples are shown in the following illustrations.

5) Employers are further reminded that under no circumstance should entry be allowed at the end of the purging time until the atmosphere is tested and shown to be within acceptable levels. If unacceptable levels are obtained, then it will be necessary to repeat the process.

6) If forced air ventilation is necessary to control any existing potential atmospheric hazards, then the blower must remain in constant operation for the duration of the permit space entry operation.

The theoretical purging time can also be determined using the ventilation calculations provided.

Alignment Chart ‑ Side 1

Confined Space VolumeEffective Blower Capacity

(Cubic Feet)(CFM)

VENTILATION CALCULATIONS

1) Determine the flow rate (Q) required to achieve 20 air changes per hour (ACH) in an underground lift station 20 ft. high, 40 ft. long, and 20 ft. wide.

EQUATION

N = Q x 60 N = Nos. of ACH
VOL Q = Ventilation Flow Rate (CFM)
60 = Constant (mins/hrs)
20 ACH = Q x 60 min/hr Vol = Space Volume (ft3)
16,000 ft3
Answer: N=20
Q = 20 AC/hr x 16,000 ft3 Q = ?
60 mins/hrs Vol = 20x40x20 = 16,000 ft.3
Answer: Q= 5,333 ft3 /min

2) A permit-required confined space 20'x30'x10' in size is found to have an initial concentration of 250 parts per million (ppm) of carbon monoxide. How long will it take to lower the concentration to 50 ppm using a portable ventilation unit with a flow rate of 1000 cfm?

EQUATION

t = -2.303 (Vol/Q) x log (C2/C1)
t = 2.303 x (6,000 ft3/1,000 ft3/min) x log (50ppm/250 ppm)
Answer: t=9.6 mins.

t = 9.6 mins. Vol = 20'x30'x10' = 6,000 ft3
t = time (minutes) C1= 250 ppm
Vol = space volume (ft3) C2 = 50 ppm
Q = ventilation flow rate (CFM) Q = 1,000 cfm
C1 = initial contaminant concentration (ppm) -2.303 = constant
C2 = final contaminant concentration (ppm) t = ?

3) What will be the concentration of hydrogen sulfide (H2S) after 20 minutes of purging a cylindrical tank (40' high with a 10' diameter)? The initial concentration is 200 ppm and the ventilation rate is 800 cfm.

EQUATION C2 = C1 x e (-Qt/Vol)

C1 = initial contaminant concentration C1 = 200 ppm
C2 = final contaminant concentration C2 = ?
e = inverse natural log Q = 800 fpm
Q = ventilation flow rate (CFM) t = time (minutes)
t = 20 mins. vol = space volume (ft3) = 40' x [TT x D2]/4]= 40' x [3.14 x 100]/4 = 40x 78.5 = 3140 ft3
Vol = Space volume (ft3)
C2= 200 ppm x e(-800 ft3/min x 20 mins/3,140 ft3)
Answer:C2= 1.2ppm

Localized Exhaust Ventilation

Dilution ventilation is seldom effective in controlling fume and dust-generating processes. However, localized exhaust ventilation is better suited to capture contaminants at or near their point of generation using hoods or enclosures with duct work connected to an exhaust fan. The contaminated air is discharged outside the confined space, thereby preventing its release into the employees' breathing zones. This type of capture control is especially effective for welding, cutting, burning and brazing operations. The ventilation system should maintain and exhaust airflow velocity of at least 100 linear feet per minute in the capture zone. Capture velocities decrease significantly as the distance between the exhaust hood inlet and welding source is increased. A good rule is to keep the exhaust inlet within six to eight inches of the source.

Some operations may require both mechanical dilution and localized exhaust ventilation to adequately control contaminants in permit spaces. Ventilation must be continuous during the entire length of the entry operation to ensure that the ventilation remains adequate and atmospheric hazards do not develop. Frequent or continuous testing must be performed for the entire length of the entry operation to ensure that the ventilation remains adequate and atmospheric hazards do not develop.

Choosing the most efficient ventilation system will depend on careful evaluation of the permit space. Some factors to consider in this evaluation process include:

  • The fan or blower capacity.
  • The configuration and size of the space.
  • The number and size of the openings.
  • The airborne contaminant, its properties, and its point of generation.
  • Positioning the blower or exhaust fan so that there are no unnecessary bends in the hose. A 90 degree bend or two can reduce efficiency significantly.
  • Increasing the length of hose will increase the friction and decrease the efficiency.
  • Make sure the ventilation system does not block the exit if only one exit is available. Make sure the authorized entrants can quickly evacuate the space.

Cleaning and Purging of Permit Spaces

Residues of hazardous chemicals or materials capable of decomposing (e.g., food products) must be cleaned from the permit space to the extent feasible prior to allowing entry. Pre‑entry cleaning and purging are necessary because even small amounts of some remaining materials can create hazardous atmospheres. Some basic steps to pre‑entry cleaning include:

  • First ensure that all material feed lines and equipment are completely and effectively isolated from the confined space.
  • Drain or pump out contents and remove as much residue as feasible
  • Test for hazardous atmosphere. If the test indicated harmful gases, vapors or mists, the space must be purged and ventilated.
  • The particular purging agent used will depend on such things as: the product in the permit space and how it might react with the purging agent; the work to be performed in the space; and the suspected hazards.
  • To remove flammable atmospheres, it may be necessary to purge the space with an inerting gas such as nitrogen, carbon dioxide, argon, etc. Other times, it may be possible to open the space to allow air to naturally ventilate the space.
  • Flammable and toxic residues on the walls and floor should also be removed prior to entry. Water is commonly used. If the residue can not be washed away, steam may be used. However, be aware that steam may not be suitable for use in some situations where the substance has a low ignition temperature or flash point. This is because the steam condensate could build up a static electric charge and create a spark, thereby igniting the flammable atmosphere. In situations where steam is needed to clean or purge a vessel, make sure that the static electricity is eliminated by bonding and grounding the steam lines and vessel. Also, allow plenty of time for the space to cool down after steam is used.
  • Occasionally, cleaning solvents may be needed. In these circumstances, make sure that the cleaning compound is compatible with the residue to be cleaned from the space.
  • Never assume that the space is safe for entry after the purging and cleaning process is completed. The atmosphere in the space must be tested prior to entry. If a hazardous atmosphere still exists or potentially exists, purge and clean the space again.
  • Continue to ventilate the space and conduct atmospheric testing frequently or continuously during the entire entry procedure.
  • In the situations where the purpose of entry is to clean the confined space, the space must first be cleaned to the extent possible from the outside. Proper personal protective equipment must be used to protect individuals from any hazards which might remain after the pre‑entry cleaning. If atmospheric hazards cannot be brought to acceptable levels by purging, cleaning and continuous ventilation, then special procedures must be put in place after properly evaluating the situation. If it is determined that an individual must enter the permit space, then these special precautions will include respiratory protection such as an airline respirator with escape bottle of Self‑Contained Breathing Apparatus (SCBA). Note, most companies only allow such types of entries during emergency situations because of the immediate dangers and risks.

Isolation and Lockout/Tagout Procedures

Prior to allowing personnel to enter into a permit space, the space must be evaluated to determine what energy sources or hazardous materials are present or potentially present. Steps must be taken to isolate the space to prevent injury to entrants by disconnecting, releasing or restraining all energy sources and/or hazardous chemical materials. Energy sources may include mechanical, electrical, pneumatic, hydraulic, thermal, radioactive and the effects of gravity; chemical hazards may include flammable, reactive, toxic, irritating, corrosive or oxygen displacing gases and vapors.

Isolation Procedures

Isolation procedures for chemical or gas lines must be instituted to eliminate potential hazards by such methods as:

  • blanking and blinding,
  • double‑block and bleed,
  • line breaking or misalignment and,
  • lockout/tagout.

Blanking and Blinding is the absolute closure of a pipe, line or duct by the fastening of a solid plate, that completely covers the bore hole, in line with the system. This plate (such as a spectacle blind or a skillet blind) should be made of the same material as the line and must be able to withstand the maximum pressure exerted by the line. This method involves installing a blank between flanges with a leak-proof gasket at a point in the conducting line as close to the confined space area as possible. The blank or blind should be marked identifying its purpose.

Double Block and Bleed is a method that uses a three‑point system to prevent leakage into the confined space, two closed valves and an open drain or vent valve located in between. Lockout or tagging the valves in their required positions provides additional protection.

Line Breaking is the intentional and physical disconnection of a pipe, line or duct. Added protection is obtained by misaligning or removing a section of the pipe, line or duct. Lines where potentially hazardous residues might remain downstream from the disconnecting point should be purged. Any disconnected line, blank or block valve should be checked with an atmospheric testing monitor to make sure it is not leaking.

Lockout/Tagout

The standard recognizes that energized parts of electrical equipment and mechanical equipment pose a significant hazard in many permit spaces. As such, circuit parts of electrical equipment must be deenergized and locked out/tagged out or both in accordance with 29 CFR 1910.333. Mechanical equipment must be locked out/tagged out or both in accordance with 29 CFR 1910.147 or guarded in accordance with Subpart O of the General Industry Standard.

General requirements for effective lockout/tagout programs include the following terms:

  • Identify and implement specific procedures, in writing, for the control of hazardous energy including preparation for shutdown, equipment isolation, lockout/tagout application, release of stored energy and verification of isolation.
  • Use locks where equipment can be locked out
  • Ensure that new equipment or overhauled equipment can accommodate locks.
  • Employ additional means to ensure safety when tags rather than locks are used.
  • Institute procedures for release of lockout/tagout including machine inspection, notification and safe positioning of employees and removal of the lockout/tagout device.
  • Obtain standardized locks and tags which indicate the identity of the employee using them and that are of sufficient quality, durability and quantity to ensure their effectiveness
  • Require that each lockout/tagout device be removed by the employee who applied the device
  • Train employees in the specific energy control procedures with training reminders as part of the annual inspection of the control procedures.
  • Adopt procedures to ensure safety when equipment must be tested during servicing, when outside contractors are working at the site, when a multiple lockout is needed for a crew servicing equipment and when shifts or personnel change.

Control of Combustible/Explosive Dust

As discussed previously, combustible dust may also pose a hazard in permit spaces. In circumstances where explosive dust concentrations may possibly meet or exceed their lower flammability limit, measures are required to control or eliminate the hazard. The following measures are recommended to provide a safe environment for the employees:

  • Housekeeping ‑ dust explosions commonly occur in series. The initial explosion stirs up more dust and this additional dust propagates a secondary explosion. The interior surfaces should be kept as clean as possible and accumulations kept to a minimum.
  • All sources of ignition must be removed from the permit space. All equipment must be in compliance with the National Fire Protection Association (NFPA) 70 -National Electrical Code for hazardous locations.
  • Static electricity must be prevented from accumulating by proper bonding and grounding methods. The relative humidity should also be maintained to approximately 40‑60%.
  • Ventilation may also be necessary to control the airborne dust hazard where needed (see Ventilation Control Section).

PERSONAL PROTECTIVE EQUIPMENT

Permit spaces may pose many types of potential hazards for personnel required to enter or working nearby. Various types of equipment may be necessary to ensure the safety of these individuals. Proper planning and evaluation will determine what equipment is needed. Equipment which may generally be required include:

HEAD PROTECTION: Head injuries are caused by falling objects or by bumping the head against a fixed object. Head protection, in the form of protective hats, must do two things ‑‑ resist penetration and absorb the shock of a blow.

Selection -Each type of class of head protectors is intended to provide protection against specific hazardous conditions. An understanding of these conditions will help in selecting the right hat for the particular situation. For industrial purposes, three classes are recognized:

Class A -general service, limited voltage protection;

Class B -utility service, high‑voltage helmets; and

Class C -special service, no voltage protection.

EYE AND FACE PROTECTION: Employers must provide eye and face protection suitable for the work to be performed and employees must use this equipment.

Suitable eye protectors must be provided where there is a potential for eye injury from machines, flying objects, glare, liquids, injurious radiation or a combination of these. Protectors must meet the following minimum requirements:

  • Provide adequate protection against the particular hazards for which they are designed:
  • Be reasonably comfortable when worn under the designated conditions:
  • Fit snugly without interfering with the movements or vision of the wearer;
  • Be capable of being disinfected;
  • Be easily cleanable; and
  • Be kept clean and in good repair.

Where employees are at risk of contact with corrosive chemicals, an eyewash with at least 15 minutes flushing capacity is required.

Design, construction, testing and use of eye and face protection must be in accordance with ANSI Z87.1-1989.

HEARING PROTECTION: Exposure to high noise levels can cause hearing loss. It may also create physical and psychological stresses such as increased blood pressure, abnormal secretion of hormones and tensing of muscles.

The extent of damage primarily depends on the intensity of the noise and the duration of exposure. Short-term exposure to noise can cause temporary hearing loss. Permanent damage is generally gradual and the result of prolonged exposure to high noise levels. There is no cure for permanent noise‑induced hearing loss, so prevention is the key.

Control measures must be instituted to prevent hearing loss. When possible, noise should be reduced or controlled by engineering controls. In situations where engineering controls cannot be used, another effective method is the use of hearing protection. Hearing protection comes in many different types such as formable premolded plugs, semi‑aural or canal caps and earmuffs. Each type has advantages and disadvantages, as well as different noise reduction ratings (NRR). The protection used should reduce the noise levels to at least 90 decibels (dB) , and 85 dB for those individuals who have experienced a significant hearing threshold shift. Under some conditions, such as when noise levels exceed 100 dB, it is necessary to use combinations of hearing protection to ensure adequate protection.

When employees are exposed to noise levels exceeding 85 decibels, OSHA requires that the exposed individual be included in a hearing conservation program. For more specific information on a hearing conservation program, refer to 29 CFR 1910.95 -Occupational Noise Exposure.

Employees must be properly trained in correct use, maintenance and the limitations of the hearing protection they use. Employees should be able to select from a variety of hearing protection to ensure that the equipment fits properly and is comfortable to wear.

In permit spaces, excessive noise can interfere with communication between the authorized entrant and attendant. In situations where excessive noise exists and the entrant must wear hearing protection, steps must be taken to ensure that communication is maintained. The communication method used must ensure that the entrant can immediately respond to an attendant's order to evacuate the space if a prohibited condition or situation arises. The method used must also enable the attendant to detect any behavioral changes in the authorized entrant. In some entry operations, tugging on a rope may be adequate to ensure effective communication. In other circumstances, an intrinsically safe electronic communication system may be needed. Some electronic communication systems have headsets which also have a noise reduction rating assigned to them.

Intrinsically safe American National Standards Institute (ANSI) Type II Sound Level Meters (SLM) should be used to determine employee noise exposure levels. An SLM is a lightweight instrument for the measurement of sound pressure levels in decibels (dB). At a minimum, the device should measure on the A‑weighted scale at the slow level response setting. The instrument should be calibrated in accordance with the manufacturer's instructions.

TORSO PROTECTION: Many potential chemical and physical hazards may threaten the torsos of permit space entrants such as contact with chemicals, temperature extremes, cuts and abrasions. Part of any pre‑entry evaluation involves determining the proper protective clothing to use to protect workers from these hazards. Manufacturers provide a large selection of protective clothing for specific applications. General selection categories include single use and reusable clothing for particulate and chemical protection, full body chemical splash protection suits, insulated workwear and specially flame‑resistant clothing.

ARM AND HAND PROTECTION: Potential hazards to the arms and hands of employees working in or around confined spaces can result in such injuries as absorption of chemicals, burns, cuts, and electrical shock. There is a wide assortment of gloves, hand pads, sleeves and wristlets for protection from various hazardous situations. The protective device should be selected to fit the job.

The following items should be considered when selecting chemical protective gloves and clothing:

  • Choose gloves designed to protect against the specific chemical of concern.
  • Keep in mind all chemicals will eventually permeate through protective clothing.
  • Combinations of protection may be required since no single protective material can protect against all chemicals.
  • Chemicals absorbed by protective clothing continue to permeate through the protective material.
  • Consult with the chemical protective clothing manufacturer to determine the appropriate material for the specific chemical of concern. Employers may also want to test the material against the chemicals to be encountered to ensure its integrity.
  • Certain occupations call for special protection. For example, electricians need special protection from shock and burns. Rubber is considered the best material for insulating gloves and sleeves. Rubber protective equipment for electrical workers must conform to the requirements established by ANSI.

FOOT AND LEG PROTECTION: For protection of feet and legs from falling or rolling objects, sharp objects, molten metal, hot surfaces and wet slippery surfaces, workers should use appropriate footguards, safety shoes, or boots and leggings. To be acceptable, safety footwear must meet ANSI requirements.

RESPIRATORY PROTECTION: OSHA standards require employers to establish and maintain a respiratory protection program whenever respirators are necessary to protect the health of employees. Before discussing the requirements of OSHA's respirator standard, it will be useful to review the various types of available respirators.

Respiratory protective devices fall into three classes: air‑purifying; atmosphere or air supplying; and combination air‑purifying and air‑supplying devices. A brief discussion of each follows:

Class 1. Air-Purifying Devices

The air-purifying device cleanses the contaminated atmosphere. Chemicals can be used to remove specific gases and vapors and mechanical filters can remove particulate matter. This type of respirator is limited in its use to those environments where the air contaminant level is within the specified concentration limitation of the device. These devices do not protect against oxygen deficiency.

"Oxygen deficiency" means that the concentration of oxygen is below the percentage found in normal air and atmosphere‑supplying respiratory protection must be provided. It exists in atmospheres where the percentage of oxygen by volume is less than 19.5 percent oxygen.

The various types of air-purifying devices include mechanical-filter cartridge; chemical‑cartridge, combination mechanical-filter/chemical-cartridge, gas masks; and powered air-purifying respirators.

Mechanical-filter respirators offer respiratory protection against airborne particulate matter, including dusts, mists, metal fumes and smokes, but do not provide protection against gases or vapors.

Chemical-cartridge respirators afford protection against low concentrations of certain gases and vapors by using various chemical filters to purify the inhaled air. They differ from mechanical-filter respirators in that they use cartridges containing chemicals to remove harmful gases and vapors.

Combination mechanical-filter/chemical‑cartridge respirators use dust, mist or fume filters with a chemical cartridge for dual or multiple chemical exposures.

Gas masks afford respiratory protection against certain gases, vapors, and particulate matter. Gas masks are designed solely to remove specific contaminants from the air; therefore, it is essential that their use be restricted to atmospheres which contain sufficient oxygen to support life. Gas masks may be used for escape only from atmospheres that are immediately dangerous to life or health (IDLH), but never for entry into such environments.

"IDLH" means an atmospheric concentration of any toxic, corrosive or asphyxiate substance that poses an immediate threat to life or would cause irreversible or delayed adverse health effects or would interfere with an individual's ability to escape from a dangerous atmosphere.

Canisters for gas masks are color‑coded according to the contaminant against which they provide protection. This information is included in the standard.

Powered air-purifying respirators protect against particulate, gases and vapors. The air-purifying element may be a filter, chemical cartridge, combination filter and chemical cartridge, or canister. The powered air-purifying respirator uses a power source (usually a battery pack) to operate a blower that passes air across the air-powered air-purifying respirator. It usually supplies air at positive pressure (relative to atmospheric) so that any leakage is outward from the facepiece. However, it is possible at high work rates to create a negative pressure in the facepiece, thereby increasing facepiece leakage.

Class 2. Atmosphere- or Air-Supplying Devices

Atmosphere- or air-supplying devices are the class of respirators that provide a respirable atmosphere to the wearer, independent of the ambient air. Atmosphere-supplying respirators fall into three groups: supplied-air respirators, self-contained breathing apparatus (SCBA), and combination-SCBA and supplied‑air respirators. A brief discussion of each follows:

Supplied-air respirators. These devices deliver breathing air through a supply hose connected to the wearer's facepiece or enclosure. The air delivered must be free of contaminants and must be from a source located in clean air. The OSHA requirements for compressed air used for breathing, including monitoring for carbon monoxide, are listed in 1910.134(d). Supplied-air respirators should only be used in nonIDLH atmospheres.

There are three types of supplied-air respirators: Type A, B and C. Type A supplied‑air respirators are also known as hose masks with blower. Air is supplied by a motor-driven or hand-operated blower through a durable, large diameter hose. Type B supplied‑air respirators are hose masks as described above without a blower. The wearer draws air through the hose by breathing. Type C supplied-air respirators are commonly referred to as air-line respirators. An air-line respirator must be supplied with respirable air conforming to Grade D Compressed Gas Association's Standard CGA G7.1-73, Commodity Specification for Air, 1973. This standard requires air to have the oxygen content normally present in the atmosphere, no more than 5 milligrams per cubic meter (mg/M3) of condensed hydrocarbon contamination, no more than 20 parts per million (ppm) carbon monoxide, no pronounced odor and a maximum of 1,000 ppm of carbon dioxide.

There are three basic classes of airline respirators --continuous-flow, demand-flow, and pressure-demand flow.

Continuous flow. A continuous-flow unit has a regulated amount of air fed to the facepiece and is normally used where there is an ample air supply such as that provided by an air compressor.

Demand flow. These air-line respirators deliver air flow only during inhalation. Such respirators are normally used when the air supply is restricted to high‑pressure compressed air cylinders. A suitable pressure regulator is required to make sure that the air is reduced to the proper pressure for breathing.

Pressure-demand flow. For those conditions where the possible inward leakage (caused by the negative pressure during inhalation that is always present in demand systems) is unacceptable and where there cannot be the relatively high air consumption of the continuous‑flow units, a pressure‑demand air‑line respirator may be the best choice. It provides a positive pressure during both inhalation and exhalation.

Types A, B, and C that are approved for abrasive blasting are designated AE, BE, and CE respectively. These respirators are equipped with additional devices designed to protect the wearer's head and neck against impact and abrasion from rebounding abrasive material and with shielding to protect the windows of facepieces, hoods and helmets.

Self‑contained breathing apparatus (SCBA) provide complete protection against toxic gases and an oxygen deficiency. The wearer is independent of the surrounding atmosphere because he or she is breathing with a system that is portable and admits no outside air. The oxygen or air supply of the apparatus itself takes care of respiratory requirements.

Self-contained Breathing Apparatus

There are two basic types of self-contained breathing apparatus: closed-circuit and open-circuit. In the closed -circuit apparatus, the exhalation is rebreathed by the wearer after the carbon dioxide has been effectively removed and a suitable oxygen concentration restored from sources composed of: compressed oxygen; or chemical oxygen; or liquid‑oxygen. In the open‑circuit apparatus, exhalation is vented to the atmosphere and is not rebreathed. There are two types of open-circuit SCBAs: demand and pressure-demand.

Combination-SCBA and supplied-air respirators are air-line respirators with an auxiliary self‑contained air supply. An auxiliary SCBA is an independent air supply that allows a person to evacuate an area or enter such an area for a very short period of time where a connection to an outside air supply can be made. These devices are approved for use in IDLH atmospheres. The auxiliary air supply can be switched on in the event the primary air supply fails to operate. This allows the wearer to escape from the IDLH atmosphere. Combination air-line respirators with auxiliary SCBA are designed to operate in three modes: continuous-flow, demand-flow, and pressure‑demand flow.

Class 3. Combination Air-purifying and Atmosphere‑Supplying Devices

This type of device is a combination of an air-line respirator with an auxiliary air-purifying attachment, which provides protection in the event the air supply fails. These respirators are available in either continuous-flow or pressure-demand flow and are most often used with a high-efficiency filter as the air purifying element. Use in the filtering mode is allowed for escape only. Because of the posititve-pressure and escape provisions, these respirators have been recommended for asbestos work.

A summary of the classification of respiratory protective devices follows:

1) Air-Purifying Devices

a. Mechanical‑filter cartridge
b. Chemical-cartridge
c. Combination mechanical‑filter/chemical cartridge
d. Gas masks
e. Powered air-purifying

2) Atmosphere or Air Supplying Devices

a. Supplied‑air

1. Type A and AE

2. Type B and BE

3. Type C and CE (Airline)

(a) Continuous-flow
(b) Demand-flow
(c) Pressure-demand flow

b. Self-contained breathing apparatus (SCBA)

1. Closed-circuit

2. Open-circuit

(a) Demand

(b) Pressure‑demand

c. Combination-SCBA and supplied‑air

1. Continuous-flow

2. Demand-flow

3. Pressure-demand flow

3) Combination Air‑purifying and Atmosphere Supplying Devices

a. Continuous‑flow

b. Pressure‑demand flow

OSHA requires employers to develop written standard operating procedures for employees who wear respiratory protection. This written program must address each element specified in 29 CFR 1910.134 (b) which are briefly outlined below.

MINIMAL ACCEPTABLE RESPIRATOR PROGRAM

Requirement Standard

Written Operating Procedures .134(b)(1), (e)(1) and (e)(3)

Proper Selection .134(b)(2), (c) and (e)(2)

Training and Fitting .134(b)(3), (e)(5) and (e)(5)(i‑iii)

Cleaning and Disinfecting .134(b)(5) and (f)(3)

Storage .134(b)(6) and (f)(5)(i‑iii)

Inspection and Maintenance .134(b)(7),(e)(4),(f)(2)(I‑v) and (f)(4)

Work Area Surveillance .134(b)(8)

Inspection/Evaluation of Program .134(b)(9)

Medical Examinations .134(b)(10)

Approved Respirators .134(b)(11)

Note to the Employer: Refer to the sample respiratory protection program provided in Appendix I.

Precautionary Equipment

Once an entrance cover is removed, the opening must be promptly guarded by a railing, temporary cover, temporary fences or other temporary barriers. This is necessary to protect individuals from falling into the space, to protect entrants from having objects fall onto them or due to vehicular hazards. Barricades and/or pylons may also be used so long as they physically block access to the work area. Additionally, warning signs are recommended to warn unauthorized individuals not to enter the area. This may be accomplished with a warning sign reading "Danger-Confined Space Entry in Progress --No Unauthorized Entry".

Communication and Communication Systems

A reliable method must be in place for attendants to monitor the activities of the authorized entrants and for the entrants to keep attendants informed of their status in the event the permit space must be evacuated. The standard allows any effective means to be used to accomplish this objective. Types of communication methods include;

1) Battery operated, voice activated communication systems.

2) Continuous electronic monitoring equipment such as televisions, cameras, etc.

3) Battery hand‑operated communications devices (e.g., two way radios).

4) Body alarm devices may also be helpful where communication between the entrant and attendant is difficult. This type of device is designed to sound an alarm if the wearer does not move during a specified period of time.

5) Continuous and uninterrupted voice contact.

6) Visual observation from outside the space by the attendant.

A clearly understandable back-up system (line-jerk signals) is suggested should the primary system fail. Failure of the primary system is sufficient cause for immediate evacuation of the permit space. Therefore, special attention must be given to ensure that the communication system is working properly, and that a device is used that has sufficient transmission range. Also, ensure outside lines of communication have been established to summon rescue services.

The exact type and extent of communication required will depend on the operation being performed and the hazards within the space. For example, work that can only be performed in an IDLH atmosphere (because engineering controls are infeasible) would necessitate the use of continuous contact monitoring equipment. In contrast, authorized entrants working in a permit space that pose only mechanical hazards would need a communication system that provides only periodic monitoring. The desired system is one that alerts the entrant of any situation where evacuation is needed and the entrant can perform self-rescue. If no means of communication is available, then the entry should be prohibited.

Retrieval Equipment

The standard requires employers to provide, maintain and ensure the use of protective equipment. This includes equipment necessary to facilitate both entry into and exit from a permit space. Whenever possible, rescues should be performed outside the confined space so rescuers are not exposed to hazardous conditions. Proper retrieval equipment generally needed for permit space entries include:

1) chest or full-body harness

2) heavy-duty life line

3) mechanical winches

4) tripods

5) wristlets

Winches should be selfbraking to prevent free falls and to hold personnel in place when raising and lowering has stopped. Additionally, tripods should have two winches; one for lowering, arresting and retrieving an entrant and a second for tools. By having two winches, the entrant would not be tempted to disconnected himself/herself from the lifeline.

A wide variety of harnesses are available. Some coveralls have been specially designed with a builtin fullbody harness for easy donning.

In deciding what type of retrieval equipment is needed for a specific entry operation, an evaluation of the permit space must be conducted with the following conditions in mind: size and configuration of the confined space; size and location of the opening; any obstacles within the space; whether or not a rescue of the entrant would be vertical or horizontal; and potential hazards within the space.

Retrieval lines are very effective in assisting in the safe removal of unconscious personnel from many permit spaces. Therefore, each authorized entrant must use a chest or full body harness, with a retrieval line attached at the center of the entrant's back near shoulder level, or above the entrant's head.

Wristlets may be used in lieu of chest or full body harness if the employer can demonstrate the use of a harness is not feasible or creates a greater hazard. Wrist harnesses are used where the entrant may need to be withdrawn through a small opening.

In some situations, however, retrieval lines have been known to pose an additional risk by creating entanglement hazard. In these particular situations, the use of retrieval lines may be inappropriate. In such cases, the following guidelines are provided to determine if retrieval lines are appropriate:

1) A permit space with obstructions or turns that prevent pull on the retrieval line from being transmitted to the entrant does not require the use of a retrieval system.

2) A permit space from which an employee being rescued with the retrieval system would be injured because of forceful contact with projections in the space does not require the use of a retrieval system.

3) A permit space that was entered by an entrant using an air supplied respirator does not require the use of a retrieval system if the retrieval line could not be controlled so as to prevent entanglement hazards with the air line.

In circumstances where retrieval lines or harnesses cannot be worn, an alternative method must be in place should an entrant need assistance. If an acceptable alternative method is not available, then entry is prohibited. In all circumstance, inspect retrieval equipment prior to use.

Portable Power Tools

Portable power tools are generally grouped according to their power source such as electrical, pneumatic, hydraulic, gasoline and power-actuated.

In confined spaces, air-operated pneumatic power tools are normally recommended to avoid the hazards associated with using these other types of portable tools. Compressors servicing any pneumatic tools must be located outside the confined space and not pose a hazard. Ensure that all safety devices are in place such as air line safety check valves, safety retainers, etc., before using air powered tools. If portable electrical tools must be used, the electrical equipment must meet the requirements of Article 500 of the National Electric Code (NEC) for the specific hazardous location. An effective grounding system must be instituted, or ground fault circuit