NIOSH Classification of Hazards in a Confined Space

Description

The National Institute of Occupational Safety and Health (NIOSH) has defined a classification scheme for the different hazards associated with being in a confined space.

Examples of a confined space:

(1) pipeline

(2) conduit accessible by manhole (sewer line, utility line, other)

(3) holding tank

(4) silo

(5) digester

Class Designation	Risk Level
A	very high
B	moderate
C	low

Parameters graded:

(1) oxygen content

(2) toxin exposure (gas, solvent, etc.)

(3) flammability

(4) general hazard

Parameter	Finding	Class
oxygen content	> 25%	A
	21.5-25%	B
	19.5-21.4% (148 to 163 mm Hg at sea level)	C
	16.1-19.4%	B
	<= 16%	A
toxicity	none	none
	less than contamination level referenced in 29 CFR Part 1910 Subpart Z	C
	greater than contamination level referenced in 29 CFR Part 1910 Subpart Z but not immediately dangerous to health	B
	immediately dangerous to life or health ("IDLH")	A
flammability	<= 10% of lower flammable limit (LFL)	C
	10.01 - 19% of lower flammable limit	B
	>= 20% of lower flammable limit	A
general hazard	none	none
	potentially hazardous	C
	dangerous but not immediately life-threatening	B
	immediately life-threatening	A

When more than one hazard is present, the assigned risk is based on the hazard with the greatest risk.

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NIOSH Classification of Hazards in a Confined Space

Description

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