Many confined space accidents occur because the workers did not realize the dangers or potential dangers within or nearby the space. Workers may not take into account the new hazards and other conditions created during work in confined spaces. Thus, it is crucial to carefully identify all confined space hazards before entering a space.
Usually, confined space incidents are caused by multiple factors. There are two primary categories of hazards:
It is critical you identify all the hazards in a space and determine how they can impact the health and safety of workers who enter this space.
A hazardous atmosphere is any atmosphere that may incapacitate, injure, or impair an employee's self-rescue or lead to acute illness or death to workers and rescuers who enter confined spaces.
The following are examples of hazardous atmospheres within a confined space:
This does not include atmospheric concentrations of substances that are not capable of causing death, incapacitation, impairment of ability to self-rescue, injury, or acute illness.
For guidance, refer to sources of information that comply with published scientific and industry information, such as a Safety Data Sheet (SDS), and National Consensus Standards from organizations such as the American Conference of Governmental Industrial Hygienists (ACGIH) and the National Institute for Occupational Safety and Health (NIOSH).
The normal atmosphere is composed approximately of 20.9% oxygen, 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, 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 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.
Oxygen enrichment refers to air containing more than 23.5 percent oxygen. This dangerous condition is an extreme fire hazard in which static electricity from materials such as hair or clothing can provide the ignition source needed to start a fire. This environment also allows any fire to burn more readily. Oxygen enrichment does not occur naturally and should be investigated.
Oxygen enrichment can be caused by leaking oxygen cylinders or hoses that have been brought into or near the space. Always ventilate confined spaces with normal, ambient air. Never use pure oxygen.
Atmospheres containing combustible or flammable gases or vapors can be dangerous because of the threat of fire and explosion.
Three ingredients are necessary for an atmosphere to become flammable or explosive:
However, the proportions of fuel and oxygen in a mixture must be within the flammable range for this mixture to be readily ignitable.
The lower explosive limit, or LEL, is the lowest atmospheric concentration of fuel in the fuel-air mixture at which a gas or vapor can explode. The lower flammable limit, or LFL, is the lowest concentration at which the gas or vapor will burn. Fuel concentrations below the LEL and LFL will not explode or burn because there is not enough fuel in the mixture and is considered too "lean".
For example, the lean flammability limit for Jet A (aviation kerosene) in air at sea level is a concentration (by volume or partial pressure) of about 0.7%. The rich flammability limit is about 4.8% by volume or partial pressure. Flammability limits are not absolute, but depend on the type and strength of the ignition source.
The highest atmospheric concentration of a gas or vapor in the fuel-air mixture that can explode is called the upper explosive limit, or UEL. The upper flammability limit, or UFL, is the maximum fuel concentration above which the mixture will not burn. Above this concentration, the mixture will not explode or burn because it has too much fuel and is considered too "rich".
The composition of a fuel vapor and air mixture can change over time and may fluctuate within a confined space. Fluctuations occur because the fuel-air mixture moves around the space, particularly when people or other things create air currents that disturb the atmosphere. Consequently, the mixture is not uniformly distributed within the space.
Gases or vapors can only be explosive or flammable between their LEL/LFL and UEL/UFL. This is called the explosive/flammable range. Substances with a wide explosive/flammable range are considered to be more hazardous since they are readily ignitable over a wider range. However, any concentration of combustible gas or vapor should be of serious concern in a confined space. Workers should be especially careful when ventilating a space containing a gas or vapor above its UEL/UFL. In order to reduce the concentration below the LEL, this procedure will first bring the gas or vapor within its explosive/flammable range. When it does, the possibility of an explosure or fire exists.
The diagram on the right shows the relationship among the lower and upper explosive/flammability limits, explosive/flammable and non-explosive/flammable regions, flash points, and the vapor pressure curve. It also reveals what happens to a vapor/air mixture as concentrations and temperatures vary.
Finely powdered dust from combustible materials such as wood, metal, or grain can be fuel for powerful explosions. Dust clouds can develop as result of handling dusty materials or when solid materials are reduced to smaller particles from processes such as grinding, drilling, or crushing.
Airborne combustible dust at an explosive concentration would obscure vision at a distance of five feet (1.52 meters) or less. A direct reading instrument may be used to measure actual dust concentrations.
Substances regarded as toxic in a confined space can cover the entire spectrum of gases, vapors, and finely-divided airborne dust in industry. Toxic gases may be present in a confined space because:
Four common types of toxic gases encountered in confined spaces are:
Remember, atmospheric changes may occur due to the work procedure, the product stored, or a nearby gas line leak. The atmosphere may be safe upon entry, but can change very quickly.
Confined spaces prevent toxic substances from escaping, diluting, or readily dissipating. Instead, substances can become trapped and a buildup occurs, whereby the concentrations of toxic substances reach dangerous levels.
The atmosphere inside a confined space can change rapidly and unexpectedly. Also, any ignition source (such as sparks from grinding or welding equipment, static electricity, or unapproved electrical equipment that is not non-sparking or even smoking) can initiate an explosion.
Irritant or corrosive atmospheres can be divided into primary and secondary groups.
Irritant gases vary widely among all areas of industrial activity. They can be found in plastics plants, chemical plants, the petroleum industry, tanneries, refrigeration industries, paint manufacturing, and mining operations.
Prolonged exposure at irritant or corrosive concentrations in a confined space may produce little or no evidence of irritation. 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.
Examples of Corrosives:
To find out information on the hazardous substances used in a confined space, read the product label and/or the SDS. Labels provide general product information, and the SDS gives useful information on proper use and handling, special precautions, and first aid treatment. When a chemical product is purchased, the manufacturer or supplier of the product provides an SDS. The SDS must be readily available to any employee who wishes to learn about a product that he or she comes into contact with. If you have any questions, contact your safety Department, the manufacturer or supplier of the product, the NIOSH Pocket Guide to Chemical Hazards, or a consultant. Here is a sample SDS.
Atmospheric testing is required for two distinct purposes:
Continual monitoring in confined spaces is necessary because there are unseen and odorless contaminants (or oxygen-deficient atmospheres) that can kill or incapacitate workers. Monitoring is the only way to detect whether a hazardous atmosphere has developed during entry. If this is the case, employees will be alerted to the change so they can leave the space immediately.
Of those contaminants that have odor, some can be detected by our senses only at low concentration. Hydrogen sulfide, for example, will deaden the sense of smell at high concentrations. Because of this, employees might assume that a confined space is safe when it is not. There is no substitute for testing the air in a confined space prior to entry. A worker can also be exposed to a contaminant through skin contact while working in a confined space.
Atmospheric monitoring is necessary whenever:
Always test for atmospheric hazards in the following order:
The atmosphere of a confined space should be analyzed using equipment of sufficient sensitivity and specificity to identify and evaluate any hazardous atmospheres that may exist or arise, so that appropriate permit entry procedures can be developed and acceptable entry conditions stipulated for that space.
Evaluation and interpretation of this data, and development of the entry procedure, should be done by, or reviewed by, a technically qualified professional (e.g., OSHA consultation service, or certified industrial hygienist, registered safety engineer, certified safety professional, certified marine chemist, etc.) based on evaluation of all serious hazards.
The atmosphere of a permit space should be tested for residues of all contaminants identified by evaluation testing to determine that residual concentrations at the time of testing and entry are within the range of acceptable entry conditions.
When monitoring for entries involving a descent into atmospheres that may be stratified, the atmospheric envelope should be tested about every 4 feet (1.22 m) in the direction of vertical travel and to each side. If a sampling probe is used, the entrant's rate of progress should be slowed to accommodate the sampling speed and detector response.
Results of testing (i.e., actual concentration, etc.) should be recorded on the permit in the space provided adjacent to the stipulated acceptable entry condition.
If entrants leave the confined space for any reason, they should once again test the atmosphere before re-entry into the confined space because it can change rapidly.
Test results that show the composition of an atmosphere to which employees are actually exposed (even if the employees are using respirators) must be available so that they can be reviewed by members of the entry team or representatives.
Electronic gas detectors and color-indicator gas detector tubes are the most common types of instruments used for determining oxygen content, lower explosive limit, and toxic atmospheres.
The typical confined space gas monitors will offer up to four independent sensors for the detection of oxygen, combustible gas, carbon monoxide, and hydrogen sulfide. Before purchasing confined space testing equipment, evaluate the instrument's:
This term refers to any condition in a permit space that would:
Permissible exposure limits, or PELs, are occupational exposure standards that refer to the maximum concentration of airborne chemicals to which nearly all healthy persons can be exposed day after day without adverse health effects. Workers exposure to concentration of materials in excess of the PEL can result in detrimental health effects, including illness and/or death.
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A 49-year-old worker suffocated inside of a chemical tank at the Port of New Orleans. The Occupational Safety and Health Administration (OSHA) said the Illinois company, Dedicated Tank Cleaning Services, sent Armond Stack and two others into a tank in October 2015 without first testing the air quality of providing them lifelines. As a result, Stack was killed and the others were hospitalized.
OSHA is proposing $226,000 in fines against the company in connection with nine safety violations. Two of the nine proposed violations were classified as “willful,” which is the most serious category. This category is reserved for situations where an employer knows of an unsafe condition or practice, but does nothing about it.
Before Stack’s death, OSHA cited the company for almost 30 violations. Many of those violations were related to failure to take proper precautions when sending workers into confined spaces filled with dangerous chemicals.
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