Describe an explosimeter or combustion gas indicator for checking tank or pump-room atmosphere and explain how it operates?
Short answer
flowchart LR
A[Sampling probe] --> B[Hand pump]
B --> C[Catalytic sensor\nheated filaments]
C --> D[Display %LEL]
D --> E[Battery]
- Instrument: Portable explosimeter (combustible gas indicator)
- Principle: Catalytic combustion on heated platinum filaments
- Parts: Sampling probe, hand pump, catalytic sensor, display, battery
- Operation: Warm up, sample, pump, oxidise, read %LEL
- Safe limit: Typically <1 %LEL (per SMS and permit-to-work)
- IMO requirement: MSC.57(67), Annex 1, para 65 – at least one portable instrument + spares + calibration means
- IACS requirement: UR F7 – at least two portable gas detectors (%LEL) + two oxygen analysers (or combined)
- UK requirement: MSN 1345, Annex 1, para 10.6.8 – accurate low-concentration readings for safe entry
- Officer’s action: Calibrate, test before entry/hot work, log readings, follow SMS/permit limits
Full answer
The full answer explains each point step by step, with the regulations and figures behind it and the discussion from other candidates. It is in the MEO Class IV section of the Marine One forum, open to members enrolled for the MEO Class IV exam.