A confined space is a space with limited entry and egress and not suitable for human inhabitants. An example is the interior of a storage tank, occasionally entered by maintenance workers but not intended for human occupancy. Hazards in a confined space often include harmful dust or gases, asphyxiation, submersion in liquids or free-flowing granular solids (for example, grain bins), electrocution, or entrapment.
Confined space accidents are of particular concern in occupational safety and health due to the hazards that they pose to the victim and subsequently to a rescue team. Confined space training outlines the skills and protocols for safe entry to confined spaces, and includes precautions such as locking and tagging out connecting piping, testing of breathable air quality, forced ventilation, observation of workers in the space, and a predetermined rescue plan with appropriate safety harnesses and other rescue equipment standing by.
Description
Although the definition of a confined space varies between jurisdictions, it is generally recognized as a space that: has limited or restricted means of entry or exit; is large enough for a person to enter to perform tasks; is not designed or configured for continuous occupancy; A utility tunnel, the inside of a boiler (only accessible when the boiler is off), the inside of a fluid storage tank, a septic tank that has contained sewage, and a small underground electrical vault are all examples of confined spaces. Ships and other vessels commonly have confined spaces due to the need for compartmentalized watertight construction. The exact definition of a confined space varies depending on the type of industry. Until recently confined spaces on a construction site were defined differently than confined spaces in General Industry such as a paper mill. That changed due to a new confined space regulation for construction. Confined spaces that present special hazards to workers, including risks of toxic or asphyxiant gas accumulation, fires, falls, flooding, and entrapment may be classified as permit-required confined spaces depending on the nature and severity of the hazard.
Even normally habitable parts of a building such as corridors or offices may take on the characteristics of a confined space, during operations that alter normal ventilation and access. For example, a room may be wrapped in plastic sheeting for painting and any vapor emitted in the room may not be dispersed by blocked ventilation ducts. But these areas would not be defined as confined spaces by OSHA.
In the United States, entry into permit-required confined spaces must comply with regulations promulgated by the Occupational Safety and Health Administration (OSHA). These regulations include developing a written program, issuing entry permits, assigning attendant(s), designating entrants, and ensuring a means of rescue.
According to the OSHA, a permit-required confined space (permit space) has the three characteristics listed above (which define a confined space) and one or more of the following: Contains or has the potential to contain a hazardous atmosphere Contains a material that has the potential for engulfing the entrant Has an internal configuration that might cause an entrant to be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross section Contains any other recognized serious safety or health hazards.
In addition to the hazards posed by the design of the space, work activities can also pose serious safety hazards (heat, noise, vapors, etc.) that must be taken into account when identifying safety measures that must be taken.
Atmospheric hazards
The most common hazard seen in confined spaces is that of atmospheric hazards. These affect air quality and present immediate hazards to health or life. Acceptable atmospheric conditions must be verified before entry, and must be monitored continuously while the space is occupied. The oxygen concentration, the presence of toxic gases, and flammable material are the three conditions that must be monitored.
According to OSHA, oxygen concentration is considered safe if it is between 19.5% and 23.5% of the total atmosphere. To protect against toxic gases, contaminants have permissible exposure limits (PELs), which are set by OSHA within the United States. Work also cannot continue if the concentration of a material reaches or exceeds 10% of its lower explosive limit.