CONFINED SPACE HAzARDS 

Introduction 

• Overview 

• Types ofConfmed Spaces 

• Reasons for Entering Confined Spaces 

Hazardous Atmospheres 

• 

• 

e 

Fla..T~f!lable Atmospheres 

Toxic Atmospheres T~+~n+ fr'n7"f'"n~1u~ '\ A tTnn~nh~rPc J.J.J.J.La.l..U. \ '-'VJ.J.V,;,J. V '-') ~LU . .I.V.;J_tJ.U.'-'.I.""'.;J 

A ..,_t....,."";,..+;.-.~Y A ~""'~hA ... .,.co ~.:>p.uy A.J.a.u..u0 ~u.uv,;,pu'-'J.""., 

General Safety Hazards 

• rv1echanical 

....., • - .._. - . - "'--- ,_ 1 - --- • communicauon rroo1em 

• Entry and Exit 

• Physical 

... .l.hermal Effects 

... Noise 

... Vibration 

... General/Physical 
CONFINED SPACE HAzARDS 

INTRODUCTION 

Overview 

The hazards encountered and associated with entering and working in confined spaces are capable 

of causing bodily injury, illness, and death to the worker. Accidents occur among workers because 

of failure to recognize that a confined space is a potential hazard. It should therefore be considered 

that the most unfavorable situation exists in every case 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 

increase the hazards of fire and explosion. 

Hazardous conditions covered in this discussion include: Hazardous Atmospheres (flammable, toxic, 

iu~tant, and asphyxiating), and General Safety Hazards (mec}l...arical, corr.Jnunicatiorls, entry and eY.it, <'-~ ... 1.. .. ,,.,;,..., 1\ a.uu puy ~u. .. a.J.). 

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 enciosed spaces with very limited openings for entry. In 

either of these cases, the space may contain mechanical equipment with moving parts. Any 

combination of these parameters wiH change the nature of the hazards encountered. Degreasers, pits, 

and certain types of storage tanks may be classified as open topped confmed spaces that usuaHy 

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. 

Open topped water tanks that appear harmless may develop toxic atmospheres such as hydrogen 

sulfide from the vaporization of contaminated water. Therefore, these gases (heavier than air) are 

a primary concern when entry into such a confined space is being planned. 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. 

Confmed spaces such as sewers, casings, tanks, silos, vaults, and compartments of ships usually have 

limited access. The problems arising in these areas are similar to those that occur in open topped 
confined spaces. However, the limited access increases the risk of injury. Gases which are heavier 

than air such as carbon dioxide and propane, may lie in a tank or vault for hours or even days after 

the containers have been opened. Because some gases are odorless, the hazard may be overlooked 

with fatal results. Gases that are lighter then air may also be trapped within an enclosed type 

confmed space, especially those with access from the bottom or side. 

Hazards specific to a confined space are dictated by: (1) the material stored or used in the confmed 

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. All the hazards of open top and limited access confined spaces may be present together 

with the additional hazard of moving parts. Digesters and boilers usually contain power-driven 

equipment which, unless properly isolated, may be inadvertently activated after entry. Such 

equipment may also contain physical hazards that further complicate the work environment and the 

entry and exit process. 

Reasons for Entering Confmed Spaces 

Entering a confmed space as part of the industrial activity may be done for various reasons. It is 

done usually 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. Potential hazards should be easier to recognize 

during construction since the confined space has not been used. The types of hazards involved will 

be limited by the specific work practices. 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. This, and all other reasons 

for entry, must be well planned before initial entry is made and the hazards must be thoroughly 

reviewed. 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. 

2 
HAZARDOUS ATMOSPHERES 

Hazardous atmospheres encountered in confined spaces can be divided into four distinct categories: 

Flammable, Toxic, Irritant and/or Corrosive, and Asphyxiating. 

Flammable - . ----- Atmosoheres 

- ----- - .. -

A flammable atmosphere generally arises from enriched oxygen atmospheres, vaporization of 

flan1.TI1Lable liquids, byproducts of \vork, cheiPical reactioP...s, concentrations of combustible dusts, and 

desorption of chemical from inner surfaces of the confined space. 

An at.uosphere becomes fla.tTuuable when the ratio of oxygen to combustible material in the air is 

neither too rich nor too lean for combustion to occur. Combustible gases or vapors will accumulate 

when there is inadequate ventilation in areas such as a confmed space. Flammable gases such as 

acetylene, butane, propane, hydrogen, methane, natural or manufactured gases or vapors from iiquid 

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, it should also be noted that lighter than air gases may rise and develop a flammable 

concentration if trapped above the opening. 

The byproducts of work procedures can generate flammable or explosive conditions within a 

confined space. Specific kinds of work such as spray painting can result in the release of explosive 

gases or vapors. Welding in a confined space is a major cause of explosions in areas that contain 

combustible gas. 

Chemical reactions forming flammable atmospheres occur when surfaces are initially exposed to the 

atmosphere, or when chemicals combine to form flammable gases. This condition arises when dilute 

sulfuric acid reacts with iron to form hydrogen or when calcium carbide makes contact with water 

to form acetylene. Other exarnples of spont::~11eous che!!lic::~l reactions that may produce explosions 

from small amounts of unstable compounds are acetylene-metal compounds, peroxides, and nitrates. 

In a dry state, these compounds have the potential to explode upon percussion or exposure to 

increased temperature. Another class of cheirJcal reactions that form fl~T.unable atmospheres ~~se 

from deposits of pyrophoric substances (carbon, ferrous oxide, ferrous sulfate, iron, etc.) that can be 

found in tanks used by the chemical and petroleum industry. These tanks containing flammable 

deposits wiH spontaneously ignite upon exposure to air. 

Combustible dust concentrations are usually found during the process of loading, unloading, and 

conveying grain products, nitrated fertiiizers, finely ground chemical products, and any other 

combustible material. High charges of static electricity, which rapidly accumulate during periods 

of relatively low humidity (below 50%), can cause certain substances to accumulate electrostatic 

charges of sufficient energy to produce sparks and ignite a flammable atmosphere. These sparks 

may also cause explosions when the right air or oxygen to dust or gas mixture is present. 

3 
Toxic Atmospheres 

The substances to be regarded as toxic in a confined space can cover the entire spectrum of gases, 

vapors, and finely-divided airborne dust in industry. The sources of toxic atmospheres encountered 

may a.rise from the following: 

(1) The manufacturing process (for example, in producing polyvinyl chloride, hydrogen chloride 

is used as \vill as vinyl chloride monomer, \.:Vhich is carcinogenic). 

(2) The product stored [removing decomposed organic material from a tank can liberate toxic 

substances, such as hydrogen sulfide rd2S)]. 

(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. This odorless, 

colorless gas that has approximately the same density as air is formed from incomplete combustion 

of organic materials such as wood, coal, gas, oil, and gasoline; it can be formed from microbial 

decomposition of organic matter in sewers, silos, and fermentation tanks. Carbon monoxide is an 

insidious toxic gas because of its poor warning properties. Early stages of CO intoxication are 

nausea and headache. Carbon monoxide may be fatal at 1000 ppm in air, and is considered 

dangerous at 200 ppm, becau..se it forms carboxyhemoglobin in the blood which prevents the 

distribution of oxygen in the body. 

Carbon monoxide is a relatively abtL'ldant colorless, odorless gas, t.l}erefore, any untested atmosphere 

must be suspect. It must also be noted that 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 cherrrical reactions or work activities, therefore fatalities due to CO poisoning 

are not confmed to any particular industry. There have been fatal accidents in sewage treatment 

plants due to decomposition products and lack of ventilation in confined spaces. Another area where 

CO results as a product of decomposition is in the formation of siio gas in grain storage elevators. 

In another area, the paint industry, varnish is manufactured by introducing the various ingredients 

into a kettle, and heating them in an inert atmosphere, usually town gas, which is a mixture of carbon 

dioxide and nitrogen. 

In welding operations, oxides of nitrogen and ozone are gases of major toxicologic importance, and 

incomplete oxidation may occur and carbon monoxide can form as a byproduct. 

Another poor work practice, which has led to fatalities, is the recirculation of diesel exhaust 

emissions. Increased CO levels can be prevented by strict control of the ventilation and the use of 

catalytic convertors. 

4 
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 of primary irritants 

are 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 of secondary irritants include benzene, carbon tetrachloride, ethyl 

cbloride, tricbloroethane, tricbJoroeLhylene, and chloropropene. 

Irritant gases vary widely among all areas of industrial activity. They can be found in plastics plants, 

chetnical plants, the petrolelliTJ. indlk'irj, tanneries, refrigeration indtkctries, paint manufactu.~.~.a.ng, and 

mining operations. 

Prolonged exposure at irritant or corrosive concentrations in a confined space may produce littie or 

no evidence of irritation. This may result in a general weakening of the defense reflexes from 

changes in sensitivity. The danger in this situation is that the worker is usually not aware of any 

increase in his/her exposure to toxic substances. 

Asphyxiating Atmospheres 

The normal atmosphere is composed approximately of 20.9% oxygen and 78.1% nitrogen, and 1% 

argon with small amounts of various other gases. Reduction of oxygen in a confined space may be 

the result of either consumption or displacement. 

The consumption of oxygen takes place during combustion of flammable substances, as in welding, 

heating, cutting, and brazing. A more subtle consumption of oxygen occurs during bacterial action, 

as in the fermentation process. Oxygen may also be consumed during chemical reactions as in the 

formation of rust on the exposed surface of the confined space (iron oxide). The number of people 

working in a confined space and the amount of their physical activity will also influence the oxygen 

consumption rate. 

A second factor in oxygen deficiency is displacement 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. Aside from the natural development of these gases, or their 

use in the chemical process, certain gases are also used as inerting agents to displace flammable 

substances and retard pyrophoric reactions. Gases such as nitrogen, argon, heiium, and carbon 

dioxide, are frequently referred to as non-toxic inert gases but have claimed many lives. The use of 

nitrogen to inert a confined space has claimed more lives than carbon dioxide. The total 

displacement of oxygen by nitrogen will cause immediate collapse and death. Carbon dioxide and 

argon, with specific gravities greater than air, may lie in a tank or manhole for hours or days after 

opening. Since these gases are colorless and odorless, they pose an immediate hazard to health 

unless appropriate oxygen measurements and ventilation are adequately carried out. 

5 
Oxygen deprivation is one form of asphyxiation. While it is desirable to maintain the atmospheric 

oxygen level at 21 o/o by volume, the body can tolerate deviation from this ideal. When the oxygen 

level falls to 17%, the first sign ofhypoxia is a deterioration to night vision which is not noticeable 

until a normal oxygen concentration is restored. Physiologic effects are increased breathing volume 

and accelerated heartbeat. Between 14-16% physiologic effects are increa.~ed breathing volume, 

accelerated heartbeat, very poor muscular coordination, rapid fatigue, and intermittent respiration. 

Between 6-10% the effects are nausea, vomiting, inability to perform, and unconsciousness. Less 

than 6%, spasmatic breathing, con\n,.llsive movements, and death in minutes. 

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. The interplay of hazards associated with a confmed space, such as the 

potential of flammable vapors or gases being present, and the build-up of static charge due to 

mechanical cleaning, such as abrasive blasting, all influence the precautions which must be taken. 

To prevent vapor leaks, flashbacks, and other hazards, workers should completely isolate the space. 

To completely isolate a confined space, the closing of valves is not sufficient. All pipes must be 

physically disconnected or isolation blanks bolted in place. Other special precautions must be taken 

in cases where flammable liquids or vapors may re-contaminate the confined space. The pipes 

blanked or disconnected should be inspected and tested for leakage to check the effectiveness of the 

procedure. Other areas of concern are steam valves, pressure lines, and chemical transfer pipes. A 

less apparent hazard is the space referred to as a void, such as double walled vessels, which must be 

given special consideration in blanking off and inerting. 

Communication Problems 

Conununication bet-ween the worker inside and the standby person outside is of uLuost importance. 

If the worker should suddenly feel distressed and not be able to summon help, an injury could 

become a fatality. Frequently, the body positions that are assumed in a confined space make it 

difficult for the standby person to detect an unconscious worker. \Vhen 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. 

6 
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 \vi!l be detennined by th.e means of access a'ld 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, the occupancy load, and the time requirement for 

exiting in event of fire or vapor incursion, and the t:hne required to rescue injured workers. 

Physical 

The hazards described in this section include thermal effects (heat and cold), noise, vibration, 

radiation, and fatigue while working in a confined space. 

Thermal Effects 

Four factors influence the interchange of heat between people and their environment. They are: (1) 

air temperature, (2) air velocity, (3) moisture contained in the air, and (4) radiant heat. Because of 

the nature and design of most confmed spaces, moisture content and radiant heat are difficult to 

control. As the body temperature rises progressively, workers will continue to function until the 

body temperature reaches approximately 1 02°F. When this body temperature is exceeded, the 

workers are less efficient, and are prone to heat exhaustion, heat cramps, or heat stroke. In a cold 

environment, certain physiologic mechanisms come into play, which tend to limit heat loss and 

increase heat production. The most severe strain in cold conditions is chilling of the extremities so 

that activity is restricted. Speci::~l precautions must be taken in cold environ...ments to prevent 

frostbite, trench foot, and general hypothermia. 

Protective insulated cloLl-.Jng for both hot and cold envirorunents \vill add additional bulk to the 

worker and must be considered in allowing for movement in the confined space and exit time. 

Therefore, air temperature of the environment becomes an important consideration when evaluating 

working conditions in confmed spaces. 

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. If the workers inside are not able to hear 

commands or danger signals due to excessive noise, the probability of severe accidents can increase. 

7 
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 

grl~llders or other hand tools which cause vibration. 

General/Physical 

Some physical hazards cannot be eliminated because of the nature of the confined space or the work 

to be performed. These hazards include such items as scaffolding, surface residues, and structural 

hazards. The use of scru.Cfolding 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. The choice of material used for scaffolding depends upon the type of work to be performed, 

the calculated weight to be supported, the surface on which the scaffolding is placed, and the 

substance previously stored in the confined space. 

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. In dealing with 

structural hazards, workers must review and enforce safety precautions to assure safety. 

Rescue procedures may require withdrawal of an injured or Wlconscious person. Careful planning 

must be given to the relationship between the internal structure, the exit opening, and the worker. 

T.f t'h~ urA-rlr~..- ;~ t;!hJ"\u~ thP AnPn;no thP ~v~tPTn Tnn~t 1nl'lnrtP ~ rP~l'.11P ~rr~n<YPTnPnt nnPr~tPrl frnm .1.~ L.l..J.'w' YVV.J..I.'\..""'.1. .I..:J: U..IJV y""' \..1..1.'-" """P'-'.l..LI..I..I.f:>' \.A..&.'-' ~J llo,J' ... ....,.&..L.&. .1..1...1."-6..., • .&..&...&.""'.I. .......... 'W' ........ ._., ...... ""' ..... ""' .................. 0._.. ...... .& ........ .&. ... "'1"" ... _ .. ...,_ ...... _ A.6. 

outside the confined space, if possible, by which the employee can be lowered and removed without 

injury. 

8 
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, impioper 

arrangement of the inlet duct, or by the substitution of 

anything othei than fiesh (noimal) aii (appioximately 

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

CIIIIUUIIl:::t ---· ·-""-Ul -~,., VCliiUU~ ,_ .. ;_. ·- ULIICI _ ......... _ ..-----\ ~Cl~C;::> }· 

-.. • T'-'- I IIC ... lCiflf;:) - .. ~- CUI -ir QIIU ""..,.,.1 """'"''"'~ VAJ~CII .... Ql ~,.~ C ~"m~+i""'o~ ~V IICLIII n::;~ """~i.rlororl \.IVII~IUvl vU 

synonymous. However, this is a dangerous assumption, 

-i .... "~ +h~ • ·~~ n~ nvu,..on in nl~l"'o nf fro~h lnnrm~l\ ~ir fnr ;:)lllvC LIIC u~c VI vAy~vll 111 tJiavv v• 11 v~•• \••v• ••u•J uu 1v1 

ventilation will expand the limits of flammability and inl"'ro~~o +ho h~"7~rrl~ nf firo ~nrl ovnln~inn 111\JI vQ._;;;)v ~llv I IU"-UI Uw VI Ill v Ql IU '-'"-t"'"'~'"'' 1. 
Types of Confined Spaces 

• Confined spaces can be categorized generally as those 

\Atifh .1"\t"\On fnn~ ~n~ \Aii+h ~ non+h +h~+ \Alifl ro~+ril"t tho n~fl lr~l VVILII VtJvll I.VtJ..;J QIIU YYILII U '"'"""t""'ll LII~L YYIII lv~LII'-'L '-11v II~'-""'"""' 

movement of air, and enciosed spaces with very iimited 

"'t'"l nn~ninn~ Ill~~- fnr 1"'1 "'I 

~ntn1 1'-1 J o fin 

\II I PithPr _1 .. 1 1-1 

~~~P ----, thP 

... •-

~n~~P _r"' ___ 11 m~v •-J r.nnt~in --· ·--•• a 

mechanicai equipment with moving parts.) 

• Degreasers, pits, and certain types of storage tanks may 

be classified as ooen toooed confined soaces that usuallv -- - ----- - --- - -- --- - .- - - - - - .- 1- - - - - I J 

contain no moving parts. However, gases that are heavier 

than air (butane. orooane. and other hydrocarbons) remain ' 1 I I ' • 1 :- ,.1--.----=--- ,.._,J ,..,ill -A"u' +" l"u' "'"in+~ ,.,horo +ho\t ~ro Ill UCtJI C~~IUII~ OIIU VVIII IIVVV LV IVVV fJVIIIL~ VVIIvl v LllvJ Cll v 

difficult to remove. 

• Other hazards may deveiop due to the work performed in 

tho l"nnfinon ~n~t"Q nr hQI"~II~Q nf l"nrrn~h!l=' rl='~irh lA~ th~t "''""' '-'~••••••""'""' -t'""'""" '-'1 ..," ____ " -· --··--··- ·--·---- .... _ .. 

a • • I I • If • r rr I I • t I accelerate tne aecompos1t1on or scarro1a1ng suppon:s ana 

electrical components. 

• ~onfined sp~ces such as sewers, casingsj tanksj silos, 

vaults, and compartments of ships usually have limited 

access which increases the risk of injury. 

2 
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 usually contain power-driven 

equipment which, unless properly isolated, may be 

inadvertently activated after entry. 

3 
Reasons for Entering Confined Spaces 

• 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. 

4 
Flammable Atmospheres 

• Generally arise from enriched oxygen atmospheres, 

vaporization of flammable liquids, byproducts of work, 

chemicai reactions, concentrations of combustibie dusts, 

and desorption of chemical from inner surfaces of the 

confined space. 

• Fiammabie gases such as acetylene, butane, piopane, 

hydrogen, methane, natural or manufactured gases or 

vapors from liquid hydrocarbons can be trapped in 

confined soaces. and since many oases are heavier than I I ,.. ;...-

aii, they vvill seek lo\t·ver levels as in pits, se\AJers, and 

various types of storage tanks and vessels. 

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

develop a flammable concentration if trapped above the 

open1ng. 

-· I I I_ ~ I -.1 1- • ... • • 1 ne oyproaucts or wort< proceaures sucn as spiay pain Ling 

can gener~te flammable or explosive conditions within a 

confined space. 

• \lv'elding in a confined space is a major cause of 

explosions in areas that contained combustible gas. 

• Combustible dust concentrations are usuaiiy found during 

+h~ "'r""o~~ nf ln~rlinn ••nln~ninn ~nrl rnnvAvinn nr:=~in Ul~ t-'IV\J~~~ VI IV~UIII~J '-IIII""..,.._III~J -••- ~-••w~J""";:J ;::,•-••• 

products, nitrated fertiiizers, fineiy ground chemicai 

products, and any other combustible material. 

5 
Toxic Atmospheres 

= The sources of toxic atmospheres encountered in confined 

spaces may arise from the following: 

(i) The manufacturing process (for exampie, in 

producing polyvinyl chloride, hydrogen chloride is 

used as wiii as vinyi chioride monomer, which is 

carcinogenic). 

(2) The product stored [removing decomposed organic 

material from a tank can liberate toxic substances, 

such as hydrogen sulfide (H2S)]. 

(3) The operation performed in the confined space (for 

ov~rnnlo \Alolrlinn nr hr~?inn \Atith m~t:::.l~ r:::.n:::.hiP nf '"'AQIIIt"IVJ VVvl'-'1111~ '\JI tJI""'.&.olll~ WWI.,II •••-•-•- v-f""--•v -· 

producing toxic fumes). 

• During ioading, unioading, formulation, and production, 

mechanical and/or human error may also produce toxic ------ ---~-~-~- --- __ ... __ ....... -~.&.L.- -•----...1 -----.a.=-- gases wn1cn are no1 pari 01 u1~ JJIC:tl 111t:::u Ut.Jt:::• c:tuu••· 

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

up in a confined space. 

• Odorless, colorless gas approximately the same 

""'~n~iftt ~~ ~ir i~ fnrrnorl frnrn inl"nrnnl~t~ rnmh••~tinn nf U~II~ILJ Q~ Qll l<i;J IVIIIIVU II VIII II l""''-"1 1 •f"•-•- v-1 1 , ___ .,,_, 1 -• 

organic materiais such as wood, coai, gas, oii, and 

n~~nlino· l"'!ln h~ fnrrn~n frnm mirrnhi::.l rlA~nmnn~itinn ~Q~VIIIIvJ '"'~II""'""'""'''''-- ••-••• ••••....;•--•-• --..,;-•••r-~···-·· 

of organic matter in sewers, siios, and fermentation 

tanks. 

6 
Toxic Atmospheres (cont'd) 

~ Early stages of CO intoxication are nausea and 

headache. May be fatal at 1 000 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 cornbustible gas indicatoi 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 

nn+ l"nnfino~ +n ~nu n~rtil"tll!lr inrl••~tn1 l=v!lrnniQ~· I lVI. \.#VIIIIIIvU I.V c;u IJ f'-'UI '-1\JUIUI II IUU.-J'-1 ~. .._"~lllt-'1'-'"'• 

.... Sewage treatment plants due to decomposition 

products and lack of ventilation in confined spaces 

.... Formation of silo gas in grain storage elevators 

7 
Irritant (Corrosive) Atmospheres 

• Irritant or corrosive atmospheres can be divided into nril"n~r\1 ~nrl ~ot"nnrl~ni nrn11n~ tJI IIIIQI J Ql IU ~vvVI IU~I ~ ~~ ""'"'I'"''-'• 

• 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 sulfui dioxide. 

• A secondary irritant is one that may produce systemic 

toxic effects in addition to surface irritation. Examples 

:--•· • ......1- """----""" "~.-h"n +~+r"'lll""hlnrirl~ o+h,,l l"'hlnrirlo 111\,IUUC LJCIILCII~, \,QIIJVII LvLI ClviiiVIIUv 7 ~I.IIJ I \JIIIVIIUv 7 

trichloroethane, trichloroethylene, and chloropropene. 

• Irritant gases vary wideiy among aii areas of industriai 

~l"+i,Ii+u ThQ\1 l"~n h~ fna1nrl in nl!:a~tir~ nl~nt~ r.hP-mir.~l ~VLIVIL~. I •• .....,~ """"''I ...,_ ·--· ·- Ill t'~--·~~- ..... ·-· .... -, .....;. ·-· ... ....;._. 

piants, the petroieum 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 mav result in a aeneral weaken ina of the 

-------., - - -1-.C---- __ Q_,_, __ .,:: .. -~ _....,.,..."",.."~~" i"" ~~"~n~i+i,,i+,., Th~ rl~nnor 

Ut::=l t::II:St:: It:: llt::At::;:) II Ulll \,IIC111~C~ Ill ~CI 1~1 Ll VI L y. I 1 lv UQI ~~~~ 

in this situation is that the worker is usually not aware of 

any inciease in his/her exposure to toxic substances. 

8 
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°/o by volume) can cause various effects including: 

..,. Level of 17%: increased breathing volume and 

accelerated heartbeat 

..,. Between 14-16o/o: increased breathing volume, 

accelerated heartbeat, very poor muscular 

coordination, rapid fatigue, and intermittent respiration 

n-L-·--- r!' A nnf. --· ·--- • ·--=..,=-- =--1-.:1:..._ • ..__ ---&-·- .,.. OeiWeen O- I U7o. rlC:IU:S~i::l, VUIIIIllrty, llli::IUIIILY LU 1Jt::IIUIIII, 

and unconsciousness 

.... Less than 6%: spasmatic breathing, convulsive --.. ·----.a.- __ .......... __ ........ ;_ -"';_. ·"'-" IIIUVt::lllt::lll~, diiU Ut::c:llll Ill IIIIIIULC~ 

9 
Asphyxiating Atmospheres (cont'd) 

• 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. 

10 
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 space. 

~ 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, 

"'-r"l,..a """"~i"~l +r~n~·or nino~ GliiU \,llt:;IIII\,QI L1 Qll~lvl tJitJv~. 

11 
General Safety Hazards 

Communication Problems 

• Communication between the worker inside and the 

standby person outside is of utmost importance. 

• When visuai monitoring of the worker is not possibie 

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 ~""'"i"-h' I i,..h+in,.. U,...nAhnnv vU\,IClY L.l~llllll~ I ICU IUIJVV~. 

12 
General Safety Hazards 

Entrv and Exit 

" 

~ -=-"'-· __ ,.. ""i,. .. i~~ i~ ,...,,f ""'~i"r ~innifil"'~n.t"o ~~ ~ nh\I~il"~l W' I::. II Ll Y C211U vAll. l.llllv I~ VI II ICljVI ~~~I 1111\JCll 1\Jv Q~ Q tJI I.J..;;Jiv~l 

limitation and is directly related to the potentiai hazard of 

+ho .t"nnfinorl ~n~I"Q '-1 lv \JVI II II lvU ..;;JtJ~'-'v. 

• The extent of precautions taken and the standby 

equipment needed to maintain a safe work area will be 

rl~b~rmin~ci hv thP- means of access and rescue. ~ ...... -~ ••••••• ~... ...,. J -· • - ••• --- -- - - --- - - - --- - ~- - - - - -- - -

• The following should be considered: 

Tvoe of confined soace to be entered .I I • 

Access to the entrance 

Number and size of openings 

tjarriers within the space 

Occupancy load 

-r"~---- -----=-----j, ~--_,,:.a.:--=--··--"'-.&+. .. -_.,.,, ___ .. 1 1me requ•rerTlt::Hil 1u1 t:::XILIIIY 111 cvt::IIL u• 111 c u• vat.Ju• 

incursion 

~ Time required to rescue injured workers 

13 
Dh,,~i,.~l u~.,~r,-1~ .-- I 1,7~1"'QI I IQ~QI '-I~ 

Thermal Effects 

• \,AJhen a body temperature of approximately 1 02°F is 

exceeded, workers are less efficient, and are prone to heat 

• 

ovh~••~+inn ho~+ t"r~rnn~ nr ho~t ~trnli'o v.I\.IICIU~'-IVII, llv~U. VI QllltJ.;;J' \JI II'-''""" ~"I '"'n.v • 

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. 

14 
Physical H·azards 

Noise 

e 1'-Joise problems are usually intensified in confined sp;::)ces 

because the interior tends to cause sound to reverberate 

and thus expose the worker to higher sound levels than 

those found in an open environrr~ent. 

• This intensified noise increases the risk of hearing 

damage to workers which could result in temporary or 

permanent loss of hearing. 

enough to cause hearing damage may still disrupt verbal 

,-.nrnrvu lnil"~tinn \Alifh fh~ ~m~rn~nrV ~t~nnhV nP.r~nn nn the \JVIIIIIIUIIIVg'-1\JII VWI"II "'1'-' '-'•••-·~-••vJ '-•-••--J .... ~ . ._._ .. ._ ..... ....# 

exterior of the confined space. 

15 
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. 

16 
Dh,,~i"~l u~.,~rrl~ I I I.J~I"'QI I IQ&.QI U~ 

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 scaffoiding in confined spaces has contributed 

to many accidents caused by workers or materials falling, 

improper use of guard raiis, and iack of maintenance to 

insure worker safety. 

• Surface residues in confined spaces can increase the 

aiready hazardous conditions of electrical shock, reaction 

of incompatible materials, liberation of toxic substances, 

and bodiiy injury due to slips and falls. 'vAv'ithout protective 

clothing, additional hazards to health may arise due to 

surface residues. 

- t::".&.-. ·-"· ·--· ._ ____ ..... _ .... : ........ :_ - ---~-- ..... ----- -· •-k -- 1.--.--"·-- • vll Ul,;lUI Cll IICI£CII U~ Will Ill I a \JUIIIIIICU ~fJa\Jt::: ~U\JII a~ UCliiiC~ 

in horizontal tanks, trays in vertical towers, bends in 

.... ·---•- -· ~- .. k--..... -~ .. u-~· ... _. ~-~a..-.- .. ~ ,.... .. ~""'ff"""•,..ir"t,.. lUI II U:::l~, UVCIIICCIU ~1.1 \,lUI Cll IIICIIIUCI ;::,, VI ;:)\,Q IVIUIII~ 

installed for maintenance constitute physical hazards, 

• o~~"• •~ 1"'\r""""~A••r~~ n"'\~\1 ror11 1iro \AJithrlr~:3\AJ~I nf ~n ini11rorl ~C;:)\,UC IJI VvCUUI Cv IIIDJ I v~UII v VV niiUI gyyga VI Ql I II IJ'-U '-'-~ 

or unconscious person. Careful planning must be given to 

+ho rol~+inn~hin hohAioon tho intorn~l c:.trlll"fl 1ro tho t::\Vit Lllv lviQLIVII~IIItJ Uv~VVvvll ~llv IIIL'-'1 1...,.1 """"1'-~""'-~1'-'J "11'-' "'"•" 

opening, and the worker. 

17