CMC CMC Toxic Gas Detection & Monitoring 1

Question 1

What is the IDLH (Immediately Dangerous to Life or Health) concentration for hydrogen sulfide (H2S)?

Accepted Answer

100 ppm

Answer

NIOSH established the IDLH for hydrogen sulfide at 100 ppm, above which escape without respiratory protection becomes impossible.

Question 2

Which instrument is most commonly used to detect oxygen-deficient atmospheres in marine confined spaces?

Accepted Answer

Electrochemical oxygen sensor

Answer

Electrochemical oxygen sensors are the standard instrument for detecting oxygen-deficient atmospheres, providing continuous real-time O2 readings.

Question 3

What minimum oxygen concentration must a marine confined space atmosphere maintain for safe entry without SCBA?

Accepted Answer

19.5%

Answer

OSHA and NFPA 306 require a minimum of 19.5% oxygen by volume for an atmosphere to be considered safe for entry without supplied-air respirators.

Question 4

A photoionization detector (PID) is best suited for detecting which class of compounds in marine spaces?

Accepted Answer

Volatile organic compounds (VOCs)

Answer

PIDs use UV light to ionize molecules and are highly sensitive to volatile organic compounds such as benzene, toluene, and styrene.

Question 5

What does a Lower Explosive Limit (LEL) reading of 10% on a combustible gas indicator actually represent?

Accepted Answer

The gas concentration is 10% of the LEL value

Answer

A 10% LEL reading means the combustible gas concentration is 10% of the lower explosive limit — not 10% of the total atmosphere.

(CMC) Certified Marine Chemist Practice Test