When providing GFE services, __ is considered IDLH.

When providing GFE services, __ is considered IDLH.

• A. A void with a history of 35 ppm of H2S
• B. A void with 15 ppm of H2S
• C. A void with 100 ppm of H2S
• D. A void with 5 ppm of H2S

Answer: (A)

In gas-free work, an atmosphere is considered IDLH when it could cause death or severe injury before rescue, and hydrogen sulfide is especially dangerous in confined spaces because dangerous pockets can exist even when readings are not high on first glance. If a void has a history of hydrogen sulfide presence, that history means the space could still harbor toxic gas or form dangerous concentrations when ventilation changes, so it must be treated as IDLH until thorough gas testing proves otherwise. A void with a history of 35 ppm H2S fits this risk, so it’s treated as IDLH for GFE entry. The other scenarios lack that historical contamination context (they would be evaluated based on current readings and established exposure limits, not just a past observation).

In gas-free work, an atmosphere is considered IDLH when it could cause death or severe injury before rescue, and hydrogen sulfide is especially dangerous in confined spaces because dangerous pockets can exist even when readings are not high on first glance. If a void has a history of hydrogen sulfide presence, that history means the space could still harbor toxic gas or form dangerous concentrations when ventilation changes, so it must be treated as IDLH until thorough gas testing proves otherwise. A void with a history of 35 ppm H2S fits this risk, so it’s treated as IDLH for GFE entry. The other scenarios lack that historical contamination context (they would be evaluated based on current readings and established exposure limits, not just a past observation).