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### | A-Z Index Safety and Health Topics> Small Business Training > Confined Space Hazards 

## CONFINED SPACE HAZARDS

Introduction

◾ Overview

◾ Types of Confined Spaces

◾ Reasons for Entering Confined Spaces Hazardous Atmospheres

◾ Flammable Atmospheres

◾ Toxic Atmospheres

◾ Irritant (Corrosive) Atmospheres

◾ Asphyxiating Atmospheres General Safety Hazards

◾ Mechanical

◾ Communication Problem

◾ Entry and Exit

◾ Physical

◾ Thermal Effects

◾ Noise

◾ Vibration

◾ General/Physical

Discussion/Overheads - 1.91 MB

Student Handouts -253 K Self-Inspection Checklist
CONFINED SP ACE HAZARDS
INTRODUCTION Overview The hazards encountered and associated wi th entering and working in confined spaces are capable of causing bodily injury, illness, and death to the worker. Accidents occur amon g workers because of failure to recognize that a confined space is a potential hazard. It should th erefore be considered that the most unfav orable 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 re stricted areas within the confin ed space, voids, the nature of the contaminants present, the size of the space, the type of work to be performe d, and the number of people involved should be considered. The ventilation air should not create an additional ha zard 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% argo n with small amounts of various other gases). The terms air and oxygen are sometimes considered synonymous. However, this is a da ngerous assumption, since the use of oxygen in place of fresh (normal) air fo r ventilation will expand th e limits of flammability an d increase the hazards of fire and explosion. Hazardous conditions covered in this discussion include: Hazardous Atmospheres (flammable, toxic, irritant, and asphyxiating), and General Safety Hazards (mechanica l, communications, entry and exit, and physical). http://www.osha.gov/SLTC/smallbusiness/sec12.html Go APR MAY J U 

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8 /4/201 5 http://web.archive.org/web/20070528170531/http:/www.osha.gov/SLTC /smallbusiness/sec1...contain mechanical equipment with moving parts. Any combin ation of these parameters wi ll change the nature of the hazards encountered. Degreasers, pits, and certain types of st orage tanks may be classified as open topped confined spaces that usually contain no moving parts. However, ga ses that are heavier than air (butane, propane, and other hydrocarbons) remain in depressions and will flow to low po ints 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 ga ses (heavier than air) are a primary co ncern 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. Confined spaces such as sewers, casings, tanks, silos, vaults, an d compartments of ships usually have limited access. The problems arising in these areas are similar to those th at occur in open topped co nfined spaces. However, the limited access increases the risk of injury. Gases which are heavier than air such as carb on dioxide and propane, may lie in a tank or vault for ho urs or even days after the containers have been opened. Because so me gases are odorless, the hazard may be overlooked with fatal results. Gases th at are lighter then air may also be trapped within an enclosed type confined space, especially those with access from the bottom or side. Hazards specific to a confined space are dictated by: (1) th e material stored or used in the confined space; as an example, damp activated carbon in a filtration tank will ab sorb oxygen, thus creating an oxygen deficient atmosphere; (2) the activity carried out, such as the fermentation of molasses that creates ethyl alco hol vapors and decreases the oxygen content of the atmosphere; or (3) the external envi ronment, 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 th at 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. Su ch equipment may also contain physical hazards that further complicate the work environment and the entry and exit process. Reasons for Entering Confined Spaces Entering a confined space as part of th e industrial activity may be done for va rious reasons. It is done usually to perform a necessary function, such as inspection, repair, ma intenance (cleaning or painting), or similar operations which would be an infrequent or irregular function of th e total industrial activity. Entry may also be made during new cons truction. Potential hazards should be ea sier to recognize du ring construction since the confined space has not been used. The types of hazards involved will be li mited by the specific work practices. When the area meets the crit eria for a confined space, all ventilation and other requirements should be enforced. One of the most difficult entries to control is that of una uthorized entry, especially wh en there are large numbers of workers and trades invo lved, such as welders, painters, electricians, and safety monitors. A final and most important reason for en try would be emergency resc ue. This, and all other reasons for entry, must be well planned before initial entry is ma de and the hazards must be thoroughlyreviewed. 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. HAZARDOUS ATMOSPHERES Hazardous atmospheres encountered in conf ined spaces can be divided into four distinct categories: Flammable, Toxic, Irritant and/or Corrosive, and Asphyxiating. Flammable Atmospheres A flammable atmosphere generally arises from enriched oxygen atmospheres, vaporizati on of flammable liquids, byproducts of work, chemical reactions, concentrations of combustible dusts, and desorption of chemical from inner surfaces of the confined space. An atmosphere becomes flammable when the ratio of oxygen tocombustible 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 confined space. Flamma ble gases such as acetylene, butane, pr opane, 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, it should also be noted that lighter than air gases may rise and develop a flammable concentration if trapped above the opening. http://www.osha.gov/SLTC/smallbusiness/sec12.html Go APR MAY J U 

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8 /4/201 5 http://web.archive.org/web/20070528170531/http:/www.osha.gov/SLTC /smallbusiness/sec1...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 examples of spontaneous chemical reactions that ma y 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 chemical reactions that form flammable atmospheres arise from deposits of pyrophoric su bstances (carbon, ferrous oxid e, ferrous sulfate, iron, etc. ) that can be found in tanks used by the chemical and petroleum industry. These tanks containing flammable deposits will spontaneously ignite upon exposure to air. Combustible dust concentrations are us ually found during the process of lo ading, unloading, and conveying grain products, nitrated fertilizers, finely ground chemical products, and any other combustible material. High charges of static electricity, which rapidly accumulate during period s of relatively low humidity (below 50%), can cause certain substances to accumulate electrostati c 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. Toxic Atmospheres The substances to be regarded as toxic in a confined space can cover the en tire spectrum of gases, vapors, and finelydivided airborne dust in industry. The sources of to xic atmospheres encountered may arise from the following: 1. The manufacturing process (for example, in producing poly vinyl chloride, hydrogen chloride is used as will as vinyl chloride monomer, which is carcinogenic). 2. The product stored [removing decompos ed organic material from a tank can liberate toxic substances, such as hydrogen sulfide (H 2 S)]. 3. The operation performed in the conf ined space (for example, welding or brazing with metals capable of producing toxic fumes). During loading, unloading, formulation, and production, mechanical and/or hum an 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 incomp lete combustion of organic ma terials such as wood, coal, gas, oil, and gasoline; it can be formed from microbia l decomposition of organic matter in sewers, silos, and fermentation tanks. Carbon monoxide is an insidious toxic gas because of its po or warning properties . Early stages of CO intoxication are nausea and headac he. Carbon monoxide may be fatal at 1000 ppm in air, and is considered dangerous at 200 ppm, because it forms carboxyhemoglobin in the blood which prev ents the distribution of oxygen in the body. Carbon monoxide is a relatively abundant colorless, od orless gas, therefore, any unt ested atmosphere must be suspect. It must also be noted that a safe reading on a combustible gas indi cator does not ensure that CO is not present. Carbon monoxide must be test ed for specifically. The formation of CO may result from chemical reactions or work activities, therefore fatalities due to CO poisoning are not confined to an y particular industry. There have been fatal accidents in sewage treatment plan ts due to decomposition products and la ck of ventilation in confined spaces. Another area where CO results as a product of decomposition is in the formation of silo 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 ex haust emissions. Increased CO levels can be prevented by strict control of th e ventilation and the use of catalytic converters. Irritant (Corrosive) Atmospheres Irritant or corrosive atmospheres can be divided into pr imary and secondary groups. The primary irritants exert no systemic toxic effects (effects on the entire body). Examples of primary irritants are chlori ne, 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 seco ndary irritants include benzene, carbon tetrachloride, ethyl chloride, trichloroethane, trichloroethylene, and chloropropene. Irritant gases vary widely among all areas of industrial acti vity. They can be found in pl astics plants, ch emical plants, the petroleum industry, tanneries, re frigeration industries, paint manufacturing, and mining operations. http://www.osha.gov/SLTC/smallbusiness/sec12.html Go APR MAY J U 

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8 /4/201 5 http://web.archive.org/web/20070528170531/http:/www.osha.gov/SLTC /smallbusiness/sec1...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. Reductio n of oxygen in a confined space may be the result of either consumption or displacement. The consumption of oxygen take s place during combustion of flammable subs tances, as in welding, heating, cutting, and brazing. A more subtle consumption of oxygen occurs du ring bacterial action, as in the fermentation process. Oxygen may also be consumed during chemical reactions asin the formation of rust on the exposed surface of the confined space (iron oxide). The number of people working in a confined sp ace and the amount of their physical activity will also influence the oxygen consumption rate. A second factor in oxygen defi ciency is displacement by another gas. Exampl es of gases that are used to displace air, and therefore reduce the oxygen level ar e helium, argon, and nitrogen. Carbon di oxide 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, cert ain gases are also used as inerting agents to displace flammable substances and retard pyrophoric reactions. Gase s such as nitrogen, argon, helium, 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 di oxide. The total displacement of oxygen by nitrogen will cause immediate collapse and de ath. Carbon dioxide and argon, with specificgravities greater than air, may lie in a tank or manhole for hours or days af ter opening. Since these gases are co lorless and odorless, they pose an immediate hazard to health unless appropriate oxygen measurements and vent ilation are adequately carried out. Oxygen deprivation is one form of asphyxiation. While it isdesirable to maintain the atmospheric oxygen level at 21% by volume, the body can tolerate deviation from this ideal. When the oxygen level falls to 17%, the first sign of hypoxia is a deterioration to night visi on which is not noticeable until a norm al oxygen concentr ation is restored. Physiologic effects are increased breath ing volume and accelerated heartbeat. Between 14-16% physiologic effects are increased breathing volume, accelerated he artbeat, very poor muscular coordina tion, rapid fatigue, and intermittent respiration. Between 6-10% the effects are nausea, vomiting, inability to perform, and unconsciousness. Less than 6%, spasmatic breathing, convulsive movements, and death in minutes. GENERAL SAFETY HAZARDS Mechanical If activation of electrical or mechanical equipment woul d 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 confined spac e, 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 in fluence the precautions which must be taken. To prevent vapor leaks, flashbacks, and other hazards, work ers should completely isolat e 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 flammabl e liquids or vapors may recontaminate the confined space. The pipes blanked or disco nnected should be inspected and tested for leakage to check the effectiveness of the procedure. Other areas of concern are steam valves, pre ssure lines, and chemical transfer pipes. A less apparent hazard is the space referred toas a void, such as double walled vessels, which must be given special consideration in blanking off and inerting. Communication Problems Communication between the worker inside and the standby person outside is of utmost importance. If the worker should suddenly feel distressed and not be able to summon help, an injury could becomea fatality. Frequently, the body positions that are assumed in a co nfined space make it difficult for the standby person to detect an unconscious worker. When visual monitoring of the worker is not possible because of the design of the co nfined space or location of the entry hatch, a voice or alarm-ac tivated explosion proof type of comm unication 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. Entry and Exit Entry and exit time is of major significan ce as a physical limitation and is direct ly related to the potential hazard of the confined space. The extent of precautions taken and the stan dby equipment needed to mainta in a safe work area will be determined by the means of access an d rescue. The following should be consid ered: type of confined space to be http://www.osha.gov/SLTC/smallbusiness/sec12.html Go APR MAY J U 

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8 /4/201 5 http://web.archive.org/web/20070528170531/http:/www.osha.gov/SLTC /smallbusiness/sec1...The hazards described in this section in clude thermal effects (heat and cold), no ise, vibration, radiation, and fatigue while working in a confined space. Thermal Effects Four factors influence the interchange of heat between peop le 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 confined spaces, moisture content an d radiant heat are difficult to cont rol. As the body temperature rises progressively, workers will continue to function until the body temp erature reaches approximately 102 o 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 mechan isms 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. Special precautions must be taken in cold environments to prev ent frostbite, trench foot, and general hypothermia. Protective insulated clothing for both ho t and cold environments will add additi onal 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 co nsideration when evaluating workin g conditions in confined spaces. Noise Noise problems are usually intensified in confined spaces be cause the interior tends to cause sound to reverberate and thus expose the worker to higher sound levels than thos e 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 ca use hearing damage may still disrupt verbal communication with the emergency standby person on the exterior of the co nfined 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. Vibration Whole body vibration may affect multiple body parts an d organs depending upon the vibration characteristics. Segmental vibration, unlike whole body vi bration, appears to be more localized in creating injury to the fingers and hands of workers using tools, such as pneumatic hammers, ro tary grinders or other hand tools which cause vibration. General/Physical Some physical hazards cannot be eliminated because of the na ture of the confined space or the work to be performed. These hazards include such items as sca ffolding, surface residues, and structur al hazards. The use of scaffolding in confined spaces has contributed to many accidents caused byworkers 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 alread y hazardous conditions of elec trical 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 co nstitute physical hazards, which are exacerbated by the physical su rroundings. In dealing with structural hazard s, workers must review and enforce safety precautions to assure safety. Rescue procedures may require withdrawal of an injured or unconscious person. Careful pla nning must be given to the relationship between the internal structure, the exit openin g, and the worker. If the work er is above the opening, the system must include a rescue arrangement operated from ou tside the confined space, if possible, by which the employee can be lowered and removed without injury.

Discussion/Overheads- 1.91 MB
Student Handouts -253 K Self-Inspection Checklist http://www.osha.gov/SLTC/smallbusiness/sec12.html Go APR MAY J U 

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8 /4/201 5 http://web.archive.org/web/20070528170531/http:/www.osha.gov/SLTC /smallbusiness/sec1...Privacy and Security Statement

### | Disclaimers Occupational Safety & Health Administration 200 Constitution Avenue, NW Washington, DC 20210 http://www.osha.gov/SLTC/smallbusiness/sec12.html Go APR MAY J U 

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