QUESTION 5.6.6

Oxygen monitoring in inert-gas spaces

Oil, ChemicalEngine Room, Engine Control Room

What is being checked

The inspector is checking whether oxygen sensors serving inert-gas generator or nitrogen-generator spaces is suitable for the gases and spaces concerned, within calibration and test limits, understood by users and linked to an effective response.

Ready onboard

0/6 complete

SUITABILITYInstrument type, measuring range and oxygen-depletion sensors, sample or diffusion arrangement, alarms, ventilation status and entry points suit the expected atmosphere and task.CALIBRATIONCalibration, sensor life, batteries, filters, sampling hoses and certificates are within maker and company limits.PRE-USE TESTA fresh-air zero and functional bump test are completed with the correct gas before use; calibration is performed when required.SAMPLINGSampling points, hose length, pump response time, different levels and remote or inaccessible portions are included.ALARM RESPONSEOfficers can explain set points, fault indications and immediate withdrawal, entry restriction, ventilation, source isolation and rescue without unprotected entry.RECORDRecords prove channel calibration, alarm transmission, ventilation and fault tests.

Practice questions

Answer aloud, then open the preparation point.

1Why is this oxygen sensors serving inert-gas generator or nitrogen-generator spaces suitable?

Match the expected gases, measuring ranges and oxygen-depletion sensors, sample or diffusion arrangement, alarms, ventilation status and entry points to the space and operation.

2What is the difference between a bump test and calibration?

A bump test proves sensor and alarm response to gas. Calibration adjusts accuracy against a known concentration.

3How long must a remote sample be drawn?

Use the maker's pump and hose response time plus instrument stabilisation, accounting for hose length and gas characteristics.

4What happens after an alarm or sensor fault?

Follow immediate withdrawal, entry restriction, ventilation, source isolation and rescue without unprotected entry; never treat a fault, inhibited channel or over-range reading as a safe atmosphere.

5Show the last complete test.

Trace channel calibration, alarm transmission, ventilation and fault tests to the identified instrument or channel and its corrective action.

Where an observation may arise

WRONG SENSOR

The instrument or oxygen-depletion sensors, sample or diffusion arrangement, alarms, ventilation status and entry points did not suit the gas, range or atmosphere.

NO BUMP TEST

Users relied on a valid calibration sticker without a pre-use functional response test.

CALIBRATION GAP

Calibration gas, certificate, sensor or battery status was expired or not traceable.

SAMPLING ERROR

Hose response time, different levels, inaccessible areas or sample conditioning were not considered.

ALARM MISUNDERSTOOD

Personnel could not explain immediate withdrawal, entry restriction, ventilation, source isolation and rescue without unprotected entry.

SYSTEM IMPAIRED

Inspection identified expired sensor, wrong alarm setting, blocked sample, disabled channel or alarm not audible at access.

Master's practical note

Challenge the whole measurement chain: atmosphere, sample point, hose, pump, sensor, display, alarm and user decision. A current calibration label proves only one part.

Equipment boundary and references

Equipment boundary: Use maker instructions for calibration gas, cross-sensitivity, poisoning, oxygen requirements and sampling limitations. Never use a catalytic sensor in an inert atmosphere unless approved for that purpose.

References

OCIMF SIRE 2.0 Question Library Part 1, Version 1.0, Question 5.6.6
SOLAS Chapter II-2
OCIMF ISGOTT

Last reviewed: 2026-09-13