Hazards associated with entering and working in confined spaces are capable of causing serious injuries or death. Because of dangers, the American Society of Safety Engineers (ASSE) has recently approved the new American National Standards Institute (ANSI) confined spaces consensus standard.
ASSE says the purpose of the revised standard (ANSI/ASSE Z117.1-2009, Safety Requirements for Confined Spaces) is to “provide for the minimum performance requirements necessary in developing and implementing a comprehensive confined space program for the protection of workers.”
The standard, which becomes effective on November 2, establishes minimum safety requirements for entering, exiting, and working in confined spaces at normal atmospheric pressure. It does not, however, apply to underground mining, tunneling, caisson work, intentionally inert confined spaces, or other similar tasks that have their own established national consensus standards.
You can get more information or obtain a copy of the standard at the ASSE website.
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Hazardous Atmospheres a Major Concern
After reviewing 200 confined space fatality cases in preparation for revising the standard, ASSE’s Z117 Accredited Standards Committee noted that approximately 65 percent of incidents with fatalities involved atmospheric contamination.
OSHA says that hazardous atmospheres encountered in confined spaces can be divided into four distinct categories:
- Flammable
- Toxic
- Irritant and/or Corrosive
- Asphyxiating
Flammable gases—such as acetylene, butane, propane, hydrogen, methane, natural or manufactured gases, or vapors from liquid hydrocarbons—can be trapped in confined spaces. By-products of work procedures can also generate flammable or explosive conditions within a confined space, as can chemical reactions. Combustible dust is also a concern.
Toxic substances in confined spaces can cover the entire spectrum of gases, vapors, and fine airborne dust. Sources of toxic atmospheres may include manufacturing processes, stored product, or an operation performed in the confined space. Loading, unloading, formulation, production, and mechanical and/or human error may also produce toxic gases that are not part of the planned operation. Buildup of carbon monoxide is another serious concern. There have been fatal accidents in sewage treatment plants due to decomposition products and lack of ventilation in confined spaces. Decomposition can also cause silo gas in grain storage elevators, and carbon monoxide can form as a by-product in welding operations.
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Irritant and/or corrosive atmospheres in confined spaces can be a particularly insidious hazard. Prolonged exposure to irritant and/or corrosive vapors in a confined space may produce little or no evidence of irritation. Workers are usually unaware of any increase in exposure. And that’s very dangerous, because entrants can be overcome before recognizing the problem.
Asphyxiating atmospheres in confined spaces may be the result of either consumption or displacement of oxygen. 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. The second factor in oxygen deficiency is displacement by another gas. Examples of gases that displace air and, therefore, reduce the oxygen level are helium, argon, and nitrogen. Carbon dioxide may also displace air and can occur naturally in sewers, storage bins, wells, tunnels, wine vats, and grain elevators. While it is desirable to maintain the atmospheric oxygen level at 21 percent by volume, the body can tolerate some deviation from this ideal. But when the oxygen level falls below 17 percent, entrants can die of asphyxiation if they are not promptly rescued.
Training Is the Key to Preventing Accidents
To prevent confined spaces accidents and fatalities, whether from dangerous atmospheric conditions or some other confined spaces hazard (and there are plenty of others), you have to be sure your confined spaces entrants are well trained. Effective training permits them to work safely and deal successfully with any emergency situations they may encounter inside the space.
Tomorrow, we’ll look at OSHA’s training requirements for confined spaces entrants.
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