Confined Space Signs
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Hazardous atmosphere in confined spaces
As anyone who's ever painted the inside of a tiny room with the door closed might (or might not) remember, atmospheric conditions are a major concern in any confined space, and regulators have responded by paying very close attention to occupational safety procedures in circumstances like these. OSHA 1910.134 has strict guidelines for behavior in Immediately Dangerous to Life or Health (ILDH) areas, requiring the following:
At least one employee located outside the IDLH atmosphere.
Visual, voice, or signal line communication maintained between employee(s) inside the IDLH atmosphere and outside the IDLH atmosphere.
Employee(s) located outside the IDLH atmosphere trained and equipped to provide an effective emergency response.
Employer or designee notified before employee(s) located outside the IDLH atmosphere enter for an emergency rescue.
Employer or designee to provide necessary assistance.
Employees located outside the IDLH atmosphere equipped with:
Appropriate retrieval equipment or equivalent means of rescue.
Pressure demand SCBA.
A few types of atmospheric hazard:
Normal air is 20.8-21% oxygen. Any environment with an atmospheric oxygen concentration below 19.5% is considered oxygen-deficient. If the atmosphere reaches less than 12% – which can happen as a result of air being displaced by other gases, or breathing normally in a confined, low-oxygen environment – workers may pass out even before they are able to reach a safe place; a situation that can easily result in death or life-threatening injury. Rusting metals, fermentation and some chemical reactions can also make for oxygen-deficient confined spaces.
Oxygen-enriched or flammable
It's easy to forget because it's so necessary for our everyday existence, but oxygen is a volatile chemical. It’s fairly stable in the ratios that we encounter in our everyday lives, but explosive in even slightly more concentrated quantities. Other gases like methane and even combustible dust (as occurs in grain silos) can also make an atmosphere flammable. According to OSHA, a confined space becomes hazardous if it contains "flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL)" or "airborne combustible dust at a concentration that meets or exceeds its LFL […] This concentration may be approximated at a condition in which the dust obscures vision at a distance of 5 feet (1.52m) or less."
OSHA Confined Space Safety Signs
Use signs to communicate the harmful consequences of a confined space’s hazardous atmosphere.
Toxic atmospheres
Plenty of gases can be harmful or fatal to humans in even low concentrations, and the acceptable concentration of each depends on the gas. These atmospheres are often caused by manufacturing that uses a dangerous gas, by biological processes like fermentation or decomposition, or by work that frees toxic gases that would normally be inert. Some dangerous gases like phosgene and carbon monoxide give little to no warning before becoming fatal, and must be tested for in advance, while others (such as ammonia or chlorine) do have a smell but can kill even in low concentrations.

According to OSHA 1910.146(c)(5)(ii)(C), many confined spaces have to be tested for gas concentrations before anyone enters them, then again to verify their safety once the condition has been resolved. Clearly, foremen and employers should consult their OSHA compliance teams before sending workers into any confined space.Some work cultures place hardiness and daring above safety. Don't ever make this mistake in dangerous atmospheres – surviving hazards like phosgene leaks or full grain silos isn't a matter of will or daring, but education, forethought, care and planning.

Since regulations change with some frequency, it is vital to consult both federal and local regulations.

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