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.
Specialty: Emergency Medicine, Critical Care