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Confined Space Hazards 

• The hazards encountered and associated with entering 

and working in confined spaces are capable of causing 

bodily injury, illness, and death to the worker. 

• It should always be considered that the most unfavorable 

situation exists in every confined space and that the 

danger of explosion, poisoning, and asphyxiation will be 

present at the onset of entry. 

• Before forced ventilation is initiated, information such as 

restricted areas within the confined space, voids, the 

nature of the contaminants present, the size of the space, 

the type of work to be performed, and the number of 

people involved should be considered. 

• The ventilation air should not create an additional hazard 

due to recirculation of contaminants, improper 

arrangement of the inlet duct, or by the substitution of 

anything other than fresh (normal) air (approximately 

20.9% oxygen, 78.1% nitrogen, and 1% argon with small 

amounts of various other gases). 

• The terms air and oxygen are sometimes considered 

synonymous. However, this is a dangerous assumption, 

since the use of oxygen in place of fresh (normal) air for 

ventilation will expand the limits of flammability and I Increase the hazards of fire and explosron 

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Types of Confined Spaces 

• Confined spaces can be categorized generally as 

those with open tops and with a depth that will 

restrict the natural movement of air, and enclosed 

spaces with very limited openings for entry. (In 

either case, the space may contain mechanical 

equipment with moving parts.) 

• Degreasers, pits, and certain types of storage tanks 

may be classified as open topped confined spaces 

that usually contain no moving parts. However, 

gases that are heavier than air (butane, propane, 

and other hydrocarbons) remain in depressions and 

will flow to low points where they are difficult to 

remove. 

• Other hazards may develop due to the work 

performed in the confined space or because of 

corrosive residues that accelerate the 

decomposition of scaffolding supports and electrical 

components. 

o Confined spaces such as sewers, casings, tanks, 

silos, vaults, and compartments of ships usually 

have limited access which increases the risk of 

injury. 

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Types of Confined Spaces (cont'd) 

• Hazards specific to a confined space are 

dictated by: 

1. the material stored or used in the confined 

space; as an example, damp activated 

carbon in a filtration tank will absorb oxygen, 

thus creating an oxygen deficient 

atmosphere; 

2. the activity carried out, such as the 

fermentation of molasses that creates ethyl 

alcohol vapors and decreases the oxygen 

content of the atmosphere; or 

3. the external environment, as in the case of 

sewer systems that may be affected by high 

tides, heavier than air gases, or flash floods. 

• The most hazardous kind of confined space is 

the type that combines limited access and 

mechanical devices. Digesters and boilers I 

usually-contain power-driven equipme.nt. I 

which, unless properly isolated, may be 

inadvertently activated after entry. 

~e~sons for Entering Confined~paces 

I

ll • Usually done to perform a necessary function, 

such as inspection, repair, maintenance 

(cleaning or painting), or similar operations 

which would be an infrequent or irregular 

function of the total industrial activity. 

• Entry may also be made during new 

construction. When the area meets the criteria 

for a confined space, all ventilation and other 

requirements should be enforced. 

• One of the most difficult entries to control is that 

of unauthorized entry, especially when there are 

large numbers of workers and trades involved, 

such as welders, painters, electricians, and 

safety monitors. 

• A final and most important reason for entry 

would be emergency rescue. The standby 

person and all rescue personnel should be 

aware of the structural design of the space, 

emergency exit procedures, and life support 

systems required. 

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Flammable Atmospheres 

• Generally arise from enriched oxygen atmospheres, 

vaporization of flammable liquids, byproducts of work, 

chemical reactions, concentrations of combustible 

dusts, and desorption of chemical from inner surfaces of 

the confined space. 

• Flammable gases such as acetylene, butane, propane, 

hydrogen, methane, natural or manufactured gases or 

vapors from liquid hydrocarbons can be trapped in 

confined spaces, and since many gases are heavier 

than air, they will seek lower levels as in pits, sewers, 

and various types of storage tanks and vessels. 

• In a closed top tank, lighter than air gases may rise and 

develop a flammable concentration if trapped above the 

opening. 

• The byproducts of work procedures such as spray 

painting can generate flammable or explosive 

conditions within a confined space. 

• Welding in a confined space is a major cause of 

explosions in areas that contained combustible gas. 

• Combustible dust concentrations are usually found 

during the process of loading, unloading, and conveying 

grain products, nitrated fertilizers, finely ground 

chemical products, and any other combustible material. 

Toxic Atmospheres 

• The sources of toxic atmospheres encountered in 

confined spaces may arise from the following: 

1. The manufacturing process (for example, in producing 

polyvinyl chloride, hydrogen chloride is used as will as 

vinyl chloride monomer, which is carcinogenic). 

2. The product stored [removing decomposed organic 

material from a tank can liberate toxic substances, 

such as hydrogen sulfide (H,S)]. 

3. The operation performed in the confined space (for 

example, welding or brazing with metals capable of 

producing toxic fumes). 

• During loading, unloading, formulation, and production, 

mechanical and/or human error may also produce toxic 

gases which are not part of the planned operation. 

• Carbon monoxide (CO) is a hazardous gas that may 

build up in a confined space. 

Odorless, colorless gas approximately the same 

density as air is formed from incomplete combustion of 

organic materials such as wood, coal, gas, oil, and 

gasoline; can be formed from microbial decomposition 

of organic matter in sewers, silos, and fermentation 

tanks. 

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Toxic Atmospheres (cont'd) 

• Early stages of CO intoxication are nausea and 

headache. May be fatal at 1000 ppm in air, and 

is considered dangerous at 200 ppm, because 

it forms carboxyhemoglobin in the blood which 

prevents the distribution of oxygen in the body. 

• A safe reading on a combustible gas indicator 

does not ensure that CO is not present. Carbon 

monoxide must be tested for specifically. 

• The formation of CO may result from chemical 

reactions or work activities, therefore fatalities 

due to CO poisoning are not confined to any 

particular industry. Examples: 

• Sewage treatment plants due to decomposition 

products and lack of ventilation in confined 

spaces 

• Formation of silo gas in grain storage elevators 

Irritant (Corrosive) Atmospheres 

• Irritant or corrosive atmospheres can be divided into 

primary and secondary groups. 

• The primary irritants exert no systemic toxic effects 

(effects on the entire body). Examples include 

chlorine, ozone, hydrochloric acid, hydrofluoric acid, 

sulfuric acid, nitrogen dioxide, ammonia, and sulfur 

dioxide. 

• A secondary irritant is one that may produce systemic 

toxic effects in addition to surface irritation. Examples 

include benzene, carbon tetrachloride, ethyl chloride, 

trichloroethane, trichloroethylene, and chloropropene. 

• Irritant gases vary widely among all areas of industrial 

activity. They can be found in plastics plants, chemical 

plants, the petroleum industry, tanneries, refrigeration 

industries, paint manufacturing, and mining operations. 

• Prolonged exposure at irritant or corrosive 

concentrations in a confined space may produce little 

or no evidence of irritation but may result in a general 

weakening of the defense reflexes from changes in 

sensitivity. The danger in this situation is that the L , worker is usually not aware of any increase in his/her 

exposure to toxic substances. 

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Asphyxiating Atmospheres 

• The normal atmosphere is composed 

approximately of 20.9% oxygen, 78.1% 

nitrogen, and 1% argon with small amounts 

of various other gases. 

• Decreased oxygen levels (below the 

atmospheric level of 20.9% by volume) can 

cause various effects including: 

• Level of 17%: increased breathing volume 

and accelerated heartbeat 

• Between 14-16%: increased breathing 

volume, accelerated heartbeat, very poor 

muscular coordination, rapid fatigue, and 

intermittent respiration 

• Between 6-10%: nausea, vomiting, inability to 

perform, and unconsciousness 

Less than 6%: spasmatic breathing, 

convulsive movements, and death in minutes 

I Asphyxiating Atmospheres-(cont'd) 

I 

• Reduction of oxygen in a confined space may be the 

result of either consumption or displacement. 

• Consumption of oxygen: 

Takes place during combustion of flammable 

substances, as in welding, heating, cutting, and brazing 

During bacterial action, as in the fermentation process 

During chemical reactions as in the formation of rust on 

the exposed surface of the confined space (iron oxide) 

• Rate of consumption influenced by the number of 

people working in a confined space and the amount of 

their physical activity 

• Displacement of oxygen by another gas: 

Examples of gases that are used to displace air, and 

therefore reduce the oxygen level, are helium, argon, 

and nitrogen. Carbon dioxide may also be used to 

displace air and can occur naturally in sewers, storage 

bins, wells, tunnels, wine vats, and grain elevators. 

Gases such as nitrogen, argon, helium, and carbon 

dioxide are used as inerting agents to displace 

flammable substances and retard pyrophoric reactions. 

resulting in oxygen deficient atmospheres. 

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General Safety Hazards 

Mechanical 

• If activation of electrical or mechanical 

equipment would cause injury, each piece 

of equipment should be manually isolated to 

prevent inadvertent activation before 

workers enter or while they work in a 

confined space. 

• To prevent vapor leaks, flashbacks, and 

other hazards, workers should completely 

isolate the spaee. 

• The closing of valves is not sufficient - all 

pipes must be physically disconnected or 

isolation blanks bolted in place. 

• Where flammable liquids or vapors may 

re-contaminate the confined space, the 

blanked or disconnected pipes should be 

inspected and tested for leakage. 

• Other areas of concern are steam valves, 

pressure lines, and chemical transfer pipes. 

General Safety Hazards 

Communication Problems 

• Communication between the worker inside 

and the standby person outside is of utmost 

importance. 

• When visual monitoring of the worker is not 

possible because of the design of the 

confined space or location of the entry 

hatch, a voice or alarm-activated explosion 

proof type of communication system will be 

necessary. 

• Suitable illumination of an approved type is 

required to provide sufficient visibility for 

work in accordance with the 

recommendations made in the Illuminating 

Engineering Society Lighting Handbook. 

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General Safety Hazards 

Entry and Exit 

• Entry and exit time is of major significance 

as a physical limitation and is directly 

related to the potential hazard of the 

confined space. 

• The extent of precautions taken and the 

standby equipment needed to maintain a 

safe work area will be determined by the 

means of access and rescue. 

• The following should be considered: 

• Type of confined space to be entered 

• Access to the entrance 

• Number and size of openings 

• Barriers within the space 

Occupancy load 

• Time requirement for exiting in event of fire or 

vapor incursion 

• Time required to rescue injured workers 

Physical Hazards 

Thermal Effects 

• When a body temperature of approximately 

102F is exceeded, workers are less 

efficient, and are prone to heat exhaustion, 

heat cramps, or heat stroke. 

• Special precautions must be taken in cold 

environments to prevent frostbite, trench 

foot, and general hypothermia. 

• Protective insulated clothing for both hot 

and cold environments will add additional 

bulk to the worker and must be considered 

in allowing for movement in the confined 

space and exit time. 

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Physical Hazards 

Noise 

• Noise problems are usually intensified in 

confined spaces because the interior tends 

to cause sound to reverberate and thus 

expose the worker to higher sound levels 

than those found in an open environment. 

• This intensified noise increases the risk of 

hearing damage to workers which could 

result in temporary or permanent loss of 

hearing. 

• Noise in a confined space which may not be 

intense enough to cause hearing damage 

may still disrupt verbal communication with 

the emergency standby person on the 

exterior of the confined space. 

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Physical Hazards 

Vibration 

• Whole body vibration may affect multiple 

body parts and organs depending upon the 

vibration characteristics. 

• Segmental vibration, unlike whole body 

vibration, appears to be more localized in 

creating injury to the fingers and hands of 

workers using tools, such as pneumatic 

hammers, rotary grinders or other hand 

tools which cause vibration. 

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Physical Hazards 

General/Physical 

• Some physical hazards such as scaffolding, surface 

residues, and structural hazards cannot be eliminated 

because of the nature of the confined space or the work 

to be performed. 

• The use of scaffolding in confined spaces has contributed 

to many accidents caused by workers or materials falling, 

improper use of guard rails, and lack of maintenance to 

insure worker safety. 

• Surface residues in confined spaces can increase the 

already hazardous conditions of electrical shock, reaction 

of incompatible materials, liberation of toxic substances, 

and bodily injury due to slips and falls. Without protective 

clothing, additional hazards to health may arise due to 

surface residues. 

• Structural hazards within a confined space such as 

baffles in horizontal tanks, trays in vertical towers, bends 

in tunnels, overhead structural members, or scaffolding 

installed for maintenance constitute physical hazards, 

which are exacerbated by the physical surroundings. 

• Rescue procedures may require withdrawal of an injured 

or unconscious person. Careful planning must be given 

to the relationship between the internal structure, the exit 

opening, and the worker.