Books : Permit-Required Confined Space (PRCS) : Section II: Recognition and Evaluation of Confined Space Hazards

SECTION II: RECOGNITION AND EVALUATION OF CONFINED SPACE HAZARDS

CONFINED SPACE AND PERMIT REQUIRED CONFINED SPACE RECOGNITION

The inherent dangers associated with working in permit spaces is an ever present risk for a large portion of today's workforce. Many of the accidents that have been documented are a result of employers and employees failing to recognize the hazards or potential hazards involved with entering into permit spaces. This sections is designed to assist employers and employees with the task of identifying confined spaces and permit-required confined spaces in their workplaces.

Before an employer can properly evaluate their worksite, it is important that they understand the definitions of confined space and permit-required confined space.

Confined Space

A confined space is a space that has the following characteristics:

  • Is large enough and so configured that an individual can bodily enter and perform assigned work; and
  • Has limited or restricted means for entry or exit; and
  • Is not designed for continuous employee occupancy.

Note to the Employer: All three criteria must be met for the location to be considered a confined space.

Confined spaces may include:

  • Boilers
  • Pits
  • Furnaces
  • Diked Areas
  • Sewers
  • Silos
  • Septic Tanks
  • Storage Bins
  • Tunnels
  • Hoppers
  • Manholes
  • Pumping Stations
  • Vessels
  • Digester
  • Tank Cars
  • Process Vessels
  • Wells
  • Vaults
  • Cisterns
  • Plating Tanks

Permit-Required Confined Space

Once a confined space has been identified, the next step is to determine if it is a permit-required confined space. In order for a space to be considered a permit-required space, it must first meet the criteria of a confined space. Secondly, the space must contain one or a combination of the following conditions:

  • Hazardous atmosphere,
  • Liquid or solid materials that can engulf an entrant,
  • A configuration that can trap and suffocate an entrant,
  • Mechanical or electrical hazards, or
  • Contains any other recognized serious safety and health hazards.

Non-Permit Required Confined Space

Non-permit spaces are confined spaces which do not contain or, with respect to atmospheric hazards, have the potential to contain, any hazards capable of causing death or serious physical harm. Examples of non-permit confined spaces include vented vaults, motor control cabinets, and dropped ceilings. Although they are "confined spaces", these spaces have either natural or permanent mechanical ventilation available to prevent the accumulation of a hazardous atmosphere, and they do not present engulfment or other serious hazards.

Note to the Employer: Some additional clarification is provided here concerning confined spaces, permit-required confined spaces and entry into enclosed areas:

  • The standard is intended to cover only those spaces large enough for the entire body of an employee to enter. If employees cannot totally enter the space, they should not have any difficulty withdrawing from the space. A space that cannot be entered cannot be confined; therefore, it does not pose hazards related to the difficulty of exiting the space.
  • The standard is not intended to address all locations that pose atmospheric hazards. For example, an open 55 gallon drum where an employee breaks the plane of the opening is not addressed by this standard. Provisions are already in place to protect the employee from atmospheric hazards by Subpart Z of the General Industry Standard.
  • The employee must have difficulty exiting the space. Ladders (permanent or temporary), spiral or articulated stairs will usually be considered a limited or restricted means of egress. Fixed industrial stairs will be considered a limited or restricted means of egress when the conditions or physical characteristics of the space would interfere with the ability to exit or be rescued in a hazardous situation. As a rule of thumb, if someone can easily climb or descend the stairs without using the hands to aid in the climb or descent, then the stairs are not considered to be restricting or limiting.
  • The presence of a door does not in and of itself mean that the space is not a confined space. The dimensions of a door and its location are factors in determining whether an entrant can easily escape. For example, a space such as a bag house or crawl space that has a door leading into it, but also has pipes, conducits, ducts or equipment/materials that an employee would be required to crawl over or under or squeeze around in order to escape, has limited or restricted means of exit.

  • Spaces which contain permanently installed mechanical ventilation which preludes a hazardous atmosphere from developing would not be considered a permit required confined space. This system should consist of an exhaust flue stack and low level air intakes which provide a cross draft in the space to prevent the formation of a hazardous atmosphere. If the ventilation system were to malfunction, the space would have to be reevaluated.
  • The third characteristic of confined space is that it is not designed for humans to enter work for prolonged periods without any additional consideration for safety and health. Classification of a space would be based on its condition at the time employees would enter, not on the ultimate use of the space. Some products are considered permit spaces while they are being built and entries by workers are required as part of the manufacturing process. However, after they are completed and put to use, the hazards created by the manufacturing process are not present and they are then designed and intended for continuous occupancy.

TYPES OF CONFINED SPACE HAZARDS

Hazardous Atmospheres

  • Oxygen Deficiency or Oxygen Enrichment
  • Combustible/Flammable/Explosive Gases and Vapors
  • Toxic Gases and Vapors
  • Combustible

Engulfment Hazards

Entrapment or Configuration Hazards

Mechanical Hazards

Other Hazards

  • Corrosive Chemicals (acids, cleaning solutions, etc.)
  • Electrical
  • Access with Ladders
  • Lighting (poor visibility)
  • Temperature Extremes
  • Falling/Tripping/Insecure Footing
  • Falling Objects
  • Weather Conditions

HOW CONFINED SPACE HAZARDS OCCUR

Confined space hazards occur as a result of both natural and man-made sources.

SOURCES OF CONFINED SPACE HAZARDS

  • Chemical Reactions from Products Stored in Vessels
  • Oxidation/Reduction Reactions (i.e., rusting of metals)
  • Decomposition of Organic Matter
  • Cleaning Agents (Solvents, Acids)
  • Welding, Spray Painting, Grinding
  • Inerting with Non-Flammable Gases
  • Fire and Explosion Hazards from Organic Hydrocarbon Based Substances
  • Ignition Sources from Static Electricity, Hot Work Operations, Electrical Equipment
  • Lack of Proper Training
  • Lack of Permit Entry Program
  • Loose Materials Stored in Tank (Grain, Sawdust, etc.)
  • Pyrophoric Chemicals
  • Lack of Good Safety Policies and Practices

HAZARDOUS ATMOSPHERES

Hazardous atmospheres account for a majority of the fatalities that occur in permit spaces. The standard ensures the safety of the workers by requiring pre-entry testing and frequent or continuous monitoring during the entry operation. Various types of atmospheric hazards could be encountered depending on the specific type, use, and work performed in the space. It is important to know the hazards and potential hazards which might be present and to monitor accordingly. Once the employer has determined that atmospheric hazards could exist, the standard mandates that testing be conducted in the following sequence:

  • Oxygen deficiency/oxygen enrichment>
  • Combustible gases and vapors
  • Toxic gases and vapors
  • Combustible dust

Oxygen Hazards

Air is a mixture of many gases, oxygen being just one of them. The normal oxygen concentration in air is approximately 20.9% by volume.

Oxygen Deficiency

An oxygen-deficient atmosphere is considered to exist when the oxygen level falls below 19.5% by volume. This condition could exist in a permit space from either consumption or displacement of oxygen by natural and man-made sources such as:

  • Oxygen consumption by individuals
  • Decomposition of organic matter
  • Displacement of oxygen by gases and vapors (e.g. inert gases such as nitrogen, carbon dioxide, helium, or steam used to purge tanks and vessels)
  • Oxidation of metals (e.g. rusting)
  • Combustion (e.g. fire, welding, etc.)
  • Oxygen Enrichment

Oxygen enrichment levels greater than 23.5% by volume present a serious fire hazard in permit spaces. This condition could result from leaking oxygen cylinders or lines brought into a space. Also, oxygen must never be used to ventilate a confined space.

Potential Effects of Oxygen-Deficient and Enriched Atmospheres

Oxygen Content
% by Volume

Effects and Symptoms

(at atmospheric pressure)
23.5% and above Extreme fire hazard
19.5% Minimum permissible oxygen level
15-19% Decreased ability to work strenuously. May impair coordination and may induce early smptoms in persons with coronary, pulmonary or circulatory problems
12-14% Respirations increase, pulse increases, impaired coordination, perception, judgement
10-12% Respirations further increase in rate and depth, poor judgement, lips blue
8-10% Mental failure, fainting, unconsciousness, ashen face, blueness of lips, nausea and vomiting
6-8% 8 minutes, 100% fatal; 6 minutes, 50% fatal; 4-5 minutes, recovery with treatment possible
4-6% Coma in 40 seconds, convulsions, respirations cease, death
These values are approximate and vary with the individual's state of health and his or her physical activities.

Exposures to atmospheres containing 12% or less oxygen can bring about unconsciousness without warning so quickly that the individuals cannot help or protect themselves.

Combustible/Flammable Gases and Vapors

Combustible/flammable gases and vapors can pose a significant threat of fires and/or explosion in permit spaces.

The lowest concentration (air-fuel mixture) at which a gas or vapor can ignite is called its Lower Explosive Limit (LEL) or Lower Flammable Limit (LFL). Concentrations below this limit are too lean to burn. The highest concentration that can be ignited is its Upper Explosive Limit (UEL) or Upper Flammable Limit(UFL). Above this concentration, the mixture is too rich to burn.

A gas or vapor is only explosive/combustible between its LEL and UEL, but any concentration of combustible gas or vapor should be of concern when in a confined space. Lean mixtures can collect in an area and reach a combustible level, or rich mixtures can be diluted with air to become combustible.

Lower Explosive Limit (LEL) vs. Upper Explosive Limit (UEL) for Toluene

In order for an explosion or fire to occur, all components of the "fire tetrahedron" have to be present: fuel, oxygen, ignition source, and a chain reaction.

Many provisions in the standard address prevention of fire and explosion hazards by removing components of the fire tetrahedron, including:

  • Preventing an atmosphere from containing a flammable gas, vapor, or mist concentration in excess of 10% of the Lower Explosive Limit.
  • Conducting atmospheric testing to determine the percentage of the LEL present.
  • Elimination or control of sources of ignition.

Preventive measures are discussed in greater detail in the Control Section of this document.

Toxic Atmospheres

An additional concern is the presence of toxic or potentially toxic substances existing in the permit space. These substances may come in the form of gases, vapors, mists, dusts, fumes, or radiation. The standard references Subpart Z, Toxic and Hazardous Substances (i.e. chemical hazards), and Part 1910.94-100, Subpart G, Occupational Health and Environmental Controls (e.g., non-chemicals hazards such as ionizing radiation). A hazardous atmosphere is said to exist when atmospheric concentration exceeds a dose or a permissible exposure limit (PEL) for substances published in Subparts Z and G. Additionally, any other atmospheric condition that is immediately dangerous to life or health (IDLH) must be addressed as part of the permit space entry protocol.

Substances for which OSHA has not established a dose or PEL must be evaluated by the employer to determine their hazards. Sources of information include:

  • Material Safety Data Sheets (MSDS)
  • Published information on the substance
  • Industry established exposure levels
  • National Consensus Standards, including, American Conference of Governmental Industrial Hygienists (ACGIH), National Institute of Safety and Health (NIOSH)

Subpart Z contains a list of substances for which OSHA has established PELs. PELs may be expressed as 8-hour Time Weighted Averages (TWAs), 15-minute Short Term Exposure Limits (STELs), or ceiling limits. The ACGIH Threshold Limit Values (TLVs) and NIOSH Recommended Exposure Limits (RELs) are recommended exposure limits. In the absence of an OSHA PEL, OSHA can enforce TLVs and RELs.

Toxic substances will have acute (short-term) or chronic (long-term) health effects; some have both. It is important for the employer to know which, since accurate health hazards are of an immediate concern when determining the presence of a hazardous atmosphere. Three (3) of the most common toxic gases found in permit spaces include carbon monoxide, hydrogen sulfide, and methane.

  • Carbon Monoxide

Carbon monoxide is a very toxic, colorless, odorless combustible gas that is a product of incomplete combustion. It is generated by many sources such as gasoline-powered internal combustion engines, arc welding where carbon dioxide is used as an inert gas, and fires, just to name a few. Carbon monoxide has a high affinity for the hemoglobin in blood and can quickly replace oxygen. In high concentrations, carbon monoxide can cause chemical asphyxiation.

Effect of Various CO Levels

CO Level in PPM*

Resulting Condition/Effect on Humans

50

Permissible exposure level, 8 hours (OSHA)

200

Possible mild frontal headache in 2 to 3 hours

400

Frontal headache and nausea after 1 to 2 hours

Occipital after 2-1/2 to 3-1/2 hours

800

Headache, dizziness and nausea in 45 minutes

Collapse and possibly death in 2 hours

1500

IDLH

1600

Headache, dizziness and nausea in 20 minutes

Collapse and possibly death in 2 hours

3200

Headache and dizziness in 5 to 10 minutes

Unconsciousness and danger of death in 30 minutes

6400

Headache and dizziness in 1 to 2 minutes

Unconsciousness and danger of death in 10 to 15 minutes

12,800

Immediate effect unconsciousness

Danger of death in 1 to 3 minutes

*PPM = parts per million

10,000 PPM = 1% by volume

IDLH = Immediately Dangerous to Life and Health

All values are approximate with the exception of the OSHA PEL. The effects can vary depending on the individual=s health and the type of physical activity being performed.

Source: American Industrial Hygiene Association
  • Hydrogen Sulfide

Hydrogen sulfide is a flammable, colorless gas with characteristic rotten-egg odor and is soluble in water. It is commonly found in areas where petroleum products are processed, is a by-product of manufacturing operations such as tanneries, is released during the decay of sulphur-containing organic matter and is encountered in sewers and sewage treatment plants. Hydrogen sulfide has a strong odor noticeable at low concentrations, but overall, this substance has poor warning properties because of rapid olfactory fatiuge. Employees will quickly lose their ability to smell the gas, even though the gas is still present in the space.

Effect of Various H2S Levels

H2S Level in PPM*

Resulting Condition/Effect on Humans

0.13

Minimal perceptible odor

4.60

Easily detectable, moderate odor

10.0

Beginning eye irritation

Permissible exposure level, 8 hours (OSHA, ACGIH)

27.0

Strong, unpleasant odor, but not intolerable

100

Coughing, eye irritation, loss of sense of smell after 2 to 5 minutes

200

Marked conjunctivitis (eye inflammation) and respiratory tract irritation after one hour of exposure

300

IDLH

500-700

Loss of consciousness and possibly death in 30 minutes to one hour

700-1000

Rapid unconsciousness, cessation (stopping or pausing) of respirations and death

1000-2000

Unconsciousness at once, with early cessation of respirations and death in a few minutes.

Death may occur even if individual is removed to fresh air at once.

*PPM = parts per million

10,000 PPM = 1% by volume

IDLH = Immediately Dangerous to Life and Health

All values are approximate. The effects can vary depending on the individual=s health and the type of physical activity being performed.

Source: American National Standards Institute (ANSI Standard No. Z37.2-1972)
  • Methane (Natural Gas)

Methane is a colorless, odorless, flammable gas. It is a simple asphyxiate and displaces air in a confined space. The natural decaying process of organic materials is the most common source.

  • Other Atmospheric Hazards

In addition to the above-mentioned atmospheric hazards, there are other substances which may also pose a danger to permit space entrants. These substances can result from residues remaining in vessels, cleaning solvents, welding operations, by-products from chemical reactions with cleaning solvents, leaks from lines not blocked and bled off correctly, etc.

It is very important for employers to know the particular substances that could be found in a particular permit space that will be entered. Material Safety Data Sheets (MSDS) as required by the OSHA Hazard Communication Standard (29 CFR 1910.1200) must be available for the contents of any vessels/tanks/containers and for any solvents or by-products generated. The MSDS will provide valuable information on the substance including:

1) Flammability

2) Density (heavier or lighter than air)

3) Any acute or chronic health hazards

4) Lower Explosive Limit (LEL)

5) Upper Explosive Limit (UEL)

6) OSHA Permissible Exposure Limits (PELs)

7) ACGIH Threshold Limit Values (TLVs)

8) Immediately Dangerous to Life and Health (IDLH) Levels

Note to the Employer: OSHA has determined that an atmospheric concentration of any substance that is not capable of causing death, incapacitation, impairment of ability for self-rescue, injury, or acute illness due to its health effects is not covered by this provision of the standard. An atmosphere that contains a substance at a concentration exceeding its PEL which is intended solely to prevent long-term adverse health effects is not considered to be a PRCS hazardous atmosphere on that basis alone, according to the standard.

Keeping this in mind, it is important for employers to accurately determine the health hazards associated with the specific substance(s) in the space. The substance(s) must be evaluated to see if it has either long-term (chronic) effects, acute (short-term) effects or both. Consult the Material Safety Data Sheets (MSDS) for the specific health hazard data. Substances which have Short Term Exposure Limits (STELs) and/or ceiling limits can generally be considered to have acute effects and thereby be considered a potential hazardous atmosphere.

It is important for employers to know that a space may be tested and found to have acceptable oxygen and combustible gas/vapor levels, but still have a toxic gas hazard. For this reason, the specific toxic substance must be tested and the results compared to Subpart Z or other available sources. When testing for toxic gases and vapors, it is especially important to know what substance is expected because toxic gas detectors are very specific. If the PEL is only to protect employees from long-term health effects, the atmosphere may not be a hazardous atmosphere under the Permit-Required Confined Space Standard. But, control measures must be taken such as ventilation controls, respiratory protection, etc., to ensure compliance with the OSHA General Industry Standard, subpart Z, 29 CFR 1910.1048.

  • Combustible/Explosive Dust

Combustible dust may also pose a significant hazard to employees should their airborne concentration reach the lower flammability limit for the specific dust. Some common types of combustible/explosive dust include:

Food Products Spices Metal Powders Wood Products Other Dusts
grain dusts pepper aluminum wood dust hard rubber
flour tea magnesium cellulose plastic
starches cinnamon zinc

Many other organic as well as inorganic materials, if ground finely enough, will burn and support a flame.

OSHA believes that there is currently no reliable dust-monitoring equipment available to provide on site combustible dust concentration measurements, especially at high dust levels. Therefore, OSHA suggests employers and employees safely approximate the condition visually. If the dust concentration obscures vision at a distance of five feet or less (1.52 meters), the concentration is likely excessive and control measures are required.

Steps that must be taken to prevent the potential hazard include such methods as:

  • controlling sources of ignition
  • utilization of exhaust ventilation
  • fire suppression systems
  • housekeeping

Engulfment Hazard

Engulfment is the surrounding or capturing of an individual by a liquid or finely divided loose (flowable) solid substances (e.g., sand, grain, sawdust, etc.) These substances may be already in a confined space or inadvertently allowed to enter a space and engulf a worker. Death of the occupant can be caused by suffocation or drowning. Asphyxiation of the entrant is due to inhalation, or plugging of their respiratory system, or compression of their torso. Particular care must be taken in storage containment areas (e.g., silos) where these materials may have air pockets which can collapse under the weight of an individual.

To prevent engulfment hazards, the liquid or fine bulk material should be removed from the permit space to eliminate the hazard prior to authorized entry. In situations where the material cannot be removed from the space, have the entrant wear a full-body harness and retrieval line, and only allow entry if the individual can be rapidly pulled out. Also, the space must be isolated. Isolation procedures are means to keep out any potential hazardous substance whether it be solid, liquid, or gas.

Isolation procedures include such means as:

  • Locking out and/or tagging out all electrical circuits and valves.
  • Disconnecting all lines entering the space and at a location as close to the space as possible.
  • Using double block and bleed techniques. Blanks and blinds inserted in a flange as close to the vessel as possible to completely block it off.
  • Test for leaks with an atmospheric monitoring device if toxic substances are a concern.

Entrapment of Configuration Hazards

An entrapment hazard exists when a permit space has an internal configuration that could trap or asphyxiate an entrant. Configurations which promote these types of hazards have inwardly converging walls or a floor which slopes downward and tapers to a small cross-section. Entrants can become trapped in the space or caught in machinery and severely injured or succumb to exposure or suffocation before they can be extricated. Proper permit entry procedures must be instituted.

Mechanical Hazards

Confined spaces may also pose mechanical hazards created by moving equipment or parts, and energized systems. Mechanical systems such as compressing devices, drive shafts, gears, grinding equipment, conveyors, mixers, rotors, mulchers, cutters, or the actual rotating or tumbling of the space itself are common hazards in some industries. Most accidents associated with these types of hazards are the result of not properly isolating the space. Machinery may be accidentally activated and the entrant crushed or electrocuted. Therefore, it is important to first identify any mechanical hazards present and effectively deactivate the system in accordance with standard isolation procedures including:

  • Lock out and/or tagging out all electrical circuits and valves.
  • Completely deenergize all mechanical, pneumatic, hydraulic systems.
  • Ensure all stored energy is removed from the equipment.
  • Block any equipment that could have stored energy or gravity-activated parts.
  • Guard machinery.

Other Hazards

  • Corrosive Chemicals

Corrosive chemicals may present a hazard to entrants by causing eye or skin irritation sufficient to impair their ability for self-rescue. The permit space should be drained and purged, whenever possible. Care must be taken to ensure that the purging agent (e.g. air, steam, water, surfactant, etc.) will not adversely react with the substance.

Personal protective equipment (e.g. protective clothing, gloves, boots, splash-proof goggles, etc.) must be available and worn during the entry operation. Eye wash and shower facilities, whether portable or stationary, must be available outside the space and must provide a minimum of 15-minutes of flushing capacity.

  • Noise

Excessive noise levels can be generated within permit spaces by grinding, welding, riveting, mechanical ventilation, etc. Due to sound reverberation within the space, noise levels are generally much higher than when the same task is performed outside the space. Noise levels could be high enough to interfere with communication between authorized entrant and attendant. In such circumstances, alternate or backup communication methods must be in place. The provisions outlined in the OSHA Noise Standard (1910.95) of Subpart G may also be required to protect the worker's hearing. In such cases monitoring to determine noise levels is required using a properly calibrated sound level meter. Hearing protection may also be required.

  • Electrical Equipment

Do not allow employees to take new hazards into the confined space. Routinely inspect all electrical equipment and tools, use ground fault circuit interrupters (GFCI) or low voltage transformers. If flammable/explosive atmospheres could possibly be of concern, use only explosion-proof equipment and spark-proof tools.

  • Access with Ladders

It is essential that authorized entrants be able to safely enter and quickly evacuate the permit space. Therefore, it is important to always maintain clear access to and from the space. Fixed or portable ladders are commonly used for access. In many situations ladders may be the only means of entry and egress. Therefore, ensure that proper ladder safety procedures are enforced.

  • Lighting

Adequate lighting must be provided to allow authorized entrants to safely enter and exit the confined space, and to perform their assigned tasks. If flammable or explosive atmospheres are possible, lighting must be approved for the location by being intrinsically safe. To avoid the potential of electrocution, which may be of concern when water is present or the vessel is constructed of metal, lighting must be connected to ground fault circuit interrupters (GFCI).

  • Thermal

Individuals engaged in strenuous activity in hot work environments are susceptible to heat stress exposure such as:

  • heat stroke
  • heat exhaustion
  • heat cramps
  • fainting

Individuals working in confined spaces are particularly at increased risk when wearing personal protective equipment.

  • Falling/Tripping/Insecure Footing and Falling Object Hazards

These types of hazards are common in confined space entry operations. However, just because they are common does not mean that steps cannot be taken to reduce the risk associated with them. Policies should be established and workers given hazard awareness training to help in this goal. Procedures to keep in mind include:

  • Use good housekeeping practices (e.g., picking up tools around the confined space opening).
  • Check ladders for slippery rungs. If there is any danger of falling from a ladder, have the worker wear a full-body harness attached to a fall-arresting and retrieval device.
  • Tie off portable ladders.
  • Wear the correct PPE (e.g., boots, helmets, etc.).
  • Lower the equipment and tools safely by rope or baskets; never have the worker climb a ladder carrying tools.

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