## 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 ofcausing bodily injury, illness, and death to the worker. Accidents occur among workers because offailure to recognize that a confined space is a potential hazard. It should therefore be considered that the mostunfavorable situation exists in every case and that the danger ofexplosion, poisoning, and asphyxiation will be present at the onset ofentry. Before forced ventilation is initiated, information such as restricted areas withinthe confined space, voids, the nature ofthe contaminantspresent, the size ofthe space, the type ofworkto be performed, and the number ofpeople involved should be considered. The ventilation air should not create an additional hazard due to recirculation ofcontaminants, improper arrangement ofthe inlet duct, or by the substitution ofanything other than fresh (normal) air (approximately 20.9% oxygen, 78.1% nitrogen, and 1% argon with small amounts ofvarious other gases). The terms air and oxygen are sometimes considered synonymous. However, this is a dangerous assumption, since the use of oxygen in place offresh (normal) air for ventilation will expand the limits of flammability and increase the hazards offire and explosion.
Hazardous conditionscovered inthis discussioninclude: Hazardous Atmospheres (flammable, toxic,**iu~tant,** andasphyxiating), and General 

### Safety Hazards 

### (mec}l...arical, corr.Jnunicatiorls, entry and

### eY.it,**<'-~** ...1..

.. ,,.,;,..., 1\ a.uu puy**~u.**..a.J.). Types ofConfined Spaces
Confined spaces can be categorized generally as 

### those with open tops and with a depth that will restrict the natural movement ofair, 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 ofthese parameters wiH change the nature ofthe 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 ofcontaminated 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 ofscaffolding supports and electrical components. Confmed spaces suchas sewers, casings, tanks, silos, vaults, andcompartments ofshipsusuallyhave 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 ofinjury. Gases which are heavier than air 

### such as carbon dioxide and propane, may lie in a tank or vault for hours oreven 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 ofmolasses that creates ethyl alcohol vapors and decreases the oxygen content ofthe atmosphere; or (3) the external environment, as in the case ofsewer systems that may be affected by high tides, heavier than air gases, or flash floods. The most hazardous kind ofconfined space is the type that combines limited access and mechanical devices. All the hazards ofopen top and limited access confined spaces may be present together with the additional hazard ofmoving 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 ofthe 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 ofhazards 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 ofthe most difficult entries to control is that ofunauthorized entry, especially when there are large numbers ofworkers 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 ofthe 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 ofcombustible dusts, and desorption ofchemical from inner surfaces ofthe confined space. An at.uosphere becomes fla.tTuuable when the ratio ofoxygen to combustible material 

### inthe air is neither too rich nortoo lean for combustion to occur. Combustible gases orvapors 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 orvapors from iiquid hydrocarbons canbe trapped in confined spaces, and since many gases are heavier than air, they 

### will seek lower levels as in pits, sewers, and various types ofstorage 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 iftrapped above the opening. The byproducts of work procedures can generate flammable or explosive conditions within a confined space. Specific kinds ofwork such as spray painting can result in the release ofexplosive gases or vapors. Welding 

### in a confined space is a major cause ofexplosions in areas that contain combustible gas. Chemical reactions forming flammable atmospheres occurwhen surfaces are initially exposed to the atmosphere, orwhenchemicals combineto 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 ofunstable 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 ofcheirJcal reactions that form**fl~T.unable** atmospheres**~~se** from deposits ofpyrophoric 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 ofloading, unloading, and conveying grain products, nitrated fertiiizers, finely ground chemical products, and any other combustible material. High charges ofstatic electricity, which rapidly accumulate during periods ofrelatively low humidity (below 50%), can cause certain substances to accumulate electrostatic charges ofsufficient 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 ofgases, vapors, and finely-divided airborne dust in industry. The sources oftoxic 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 orbrazing with metals capable ofproducing toxic fumes). During loading, unloading, formulation, and production, mechanical and/or human error may also produce toxic gases which are not part ofthe 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 oforganic 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 ofoxygen in the body. 

### Carbon monoxide is arelatively 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 decompositionproducts andlack ofventilation inconfined spaces. Another area where CO results as a product ofdecomposition is in the formation ofsiio gas in grain storage elevators. 

### In another area, the paint industry, varnish is manufactured by introducing the various ingredients into a kettle, andheating themin aninert atmosphere, usually town gas, whichis a mixture ofcarbon dioxide and nitrogen. 

### In welding operations, oxides ofnitrogen and ozone are gases ofmajortoxicologic 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 ofthe ventilation and the use of catalytic convertors.

4

### Irritant (Corrosive) Atmospheres
Irritant or corrosive atmospheres canbe divided into primary and secondary groups. The primary irritants exert no systemic toxic effects (effects on the entire body). Examples ofprimary 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 ofsecondary irritants include benzene, carbon tetrachloride, ethyl cbloride, tricbloroethane, tricbJoroeLhylene, and chloropropene.
Irritant gases vary widely among 

### all areas ofindustrial activity. They canbe found inplastics 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 ofthe defense reflexes from changes in sensitivity. The danger in this situation is that the worker is usually not aware ofany increase in his/her exposure to toxic substances. 

### Asphyxiating Atmospheres
The normal atmosphere is composed approximately of20.9% oxygen and 78.1% nitrogen, and 1% argon with small amounts ofvarious other gases. Reduction ofoxygen in a confined space may be the result ofeither consumption or displacement.
The consumption ofoxygentakes place during combustion offlammable substances, as inwelding, heating, cutting, and brazing. A more subtle consumption ofoxygen occurs during bacterial action, as in the fermentation process. Oxygen may also be consumed during chemical reactions as inthe formation ofrust on the exposed surface ofthe confined space (iron oxide). The number ofpeople working in a confined space and the amount oftheirphysical activity will also influence the oxygen consumption rate. A second factor in oxygen deficiency is displacement by another gas. Examples ofgases that are used to displace air, andtherefore 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 ofthese gases, ortheir 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 buthave claimed many lives. The use of nitrogen to inert a confined space has claimed more lives than carbon dioxide. The total displacement ofoxygen 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.

5Oxygen deprivation is one form ofasphyxiation. While it is desirable to maintain the atmospheric oxygen level at 21o/o by volume, the body can tolerate deviation from this ideal. When the oxygen level falls to 17%, the first sign ofhypoxiais 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 ofelectrical or mechanical equipment would cause injury, each piece ofequipment should be manually isolated to prevent inadvertent activation before workers enter or while they work in a confined space. The interplay ofhazards 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 otherhazards, workers should completely isolate the space. To completely isolate a confined space, the closing ofvalves is not sufficient. All pipes must be physically disconnected or isolationblanks bolted in place. Other special precautions must betaken in cases where flammable liquids or vapors may re-contaminate the confined space. The pipes blanked ordisconnected should be inspected and tested for leakage to check the effectiveness ofthe procedure. Other areas ofconcern 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 offand inerting. 

### Communication Problems
Conununicationbet-ween the worker inside and the standby person outside is ofuLuost 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 ofthe worker is not possible because ofthe design ofthe confined space or location ofthe entry hatch, a voice or alarm-activated explosionprooftype ofcommunication system will be necessary. Suitable illumination ofan 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 ofmajor significance as a physical limitation and is directly related to the potential hazard ofthe confined space. The extent ofprecautions taken and the standby equipment needed to maintain a safe work area 

### \vi!l be detennined 

### by th.e means ofaccess a'ld rescue. The following shouldbe considered: type ofconfined spaceto be entered, access tothe entrance, number and size ofopenings, barriers within the space, the occupancy load, and the time requirement for exiting in event offire 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. 

### ThermalEffects
Four factors influence the interchange ofheat betweenpeople and their environment. They are: (1) air temperature, (2) airvelocity, (3) moisture contained in the air, and (4) radiant heat. Because of the nature and design ofmost 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, orheat 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 ofthe 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 ofthe 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 ofhearing damage to workers which could result in temporary or permanent loss ofhearing. Noise in a confined space which may not be intense enough to cause hearing damage may still disrupt verbal communication withthe emergency standby person on the exterior ofthe confined space. Ifthe workers inside are not able to hear commands ordanger signals due to excessive noise, the probability ofsevere 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 ofworkers using tools, such as pneumatic hammers, rotary**grl~llders** or otherhand tools which cause vibration. 

### General/Physical
Somephysical hazards cannot be eliminated because ofthe nature ofthe confined space orthe work to be performed. These hazards include such items as scaffolding, surface residues, and structural hazards. The use ofscru.Cfolding in confined spaces has contributed to many accidents caused by workers ormaterials falling, improperuse ofguard rails, and lack ofmaintenance to insure worker safety. The choice ofmaterial used for scaffolding depends upon the type ofwork 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. Surfaceresidues inconfined spaces canincreasethe alreadyhazardous conditions ofelectrical shock, reaction ofincompatible materials, liberation oftoxic 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, ifpossible, 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 ofthe contaminants present, the size ofthe space, the type ofwork 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 ofthe 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 

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## synonymous. However, this is a dangerous assumption, -i

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# 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**nn~ninn~** 

### fnr**~ntn1** 

### fin 

### PithPr**~~~P** 

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## 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 

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## 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**  

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## 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 ofthe 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 ofthe 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 ofthe most difficult entries to control is that of unauthorized entry, especially when there are large numbers ofworkers 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 ofthe structural design of the space, emergency exit procedures, and life support systems required.

4

# Flammable Atmospheres

• Generally arise from enriched oxygen atmospheres, vaporization 

## offlammable liquids, byproducts ofwork, 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 iftrapped above the open1ng.

-· I I I_**~** I -.1 1- •
...• 

## • 1 

## ne oyproaucts or wort< proceaures sucn as spiay painLing 

## 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 oftoxic 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 (H 2

## S)]. 

## (3) The operation performed in the confined space (for**ov~rnnlo** 

### \Alolrlinn nr**hr~?inn** 

### \Atith**m~t:::.l~** 

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## producing toxic fumes).

• During ioading, unioading, formulation, and production, mechanical and/or human error may also produce toxic

------**---~-~-~-** --- __ ... __ .......**-~.&.L.-** 

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# -----.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 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 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 ofventilation 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 weakenina ofthe -------., 

# - 

# - -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 ofvarious 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 offlammable 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 ofthe 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 ofvalves 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 ofthe worker is not possibie because ofthe design ofthe 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 102°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 ofthe 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 ofworkers 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 ofthe 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 oftoxic 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