Hazards:

• Oxygen deficiency: the atmosphere may be depleted of oxygen (e.g. in tanks, void spaces, cargo holds, after inerting or due to rusting/biological action), causing asphyxiation.
• Toxic gases: hydrogen sulphide, carbon monoxide, hydrocarbon vapours, or other toxic gases may be present, causing poisoning.
• Flammable/explosive atmosphere: hydrocarbon vapours or other flammable gases within the flammable range can ignite/explode.
• Engulfment: in cargo holds/tanks, the person may be engulfed by cargo (grain, coal, etc.).
• Other hazards: confined space (limited access, poor visibility), moving machinery, hot surfaces, and the risk of the atmosphere changing.

Precautions:

• Follow the enclosed space entry procedure (per the ISM Code and the IMO recommendations): obtain a permit to work, and carry out a risk assessment.
• Test the atmosphere before entry (oxygen, flammable gas, toxic gas) with calibrated instruments, and continue to monitor during entry.
• Ventilate the space thoroughly before and during entry.
• Use a trained attendant at the entrance, with a means of communication and a lifeline; the entrant wears appropriate PPE and, where the atmosphere is not proven safe, a breathing apparatus.
• Ensure a rescue arrangement is in place (a rescue team, a tripod/winch, and the means to recover a casualty) before entry.
• Isolate the space (lock out/tag out any machinery, valves, or sources of gas) and ensure it cannot be flooded or pressurised.
• Never enter an enclosed space without the proper procedure, and never attempt a rescue without the correct equipment (many casualties are would-be rescuers).

Sketch: A portable oxygen analyser consists of a probe/sample line, a pump or aspirator, a sensor (an electrochemical/electrolytic cell or a paramagnetic sensor), a display (meter showing % O2), and a battery. The probe is inserted into the space (through a sampling point or a small opening), and the pump draws a sample of the atmosphere over the sensor. The sensor (e.g. an electrochemical cell with a lead/oxygen electrode) produces a current proportional to the oxygen concentration, which is displayed as % O2 (e.g. 20.9% for normal air). The instrument is calibrated against fresh air (20.9%) and a zero (nitrogen) before use.

Operation: The analyser measures the oxygen content of the sampled atmosphere; a reading below about 19.5% indicates an oxygen-deficient (unsafe) atmosphere, and entry must not be made without breathing apparatus; a reading near 20.9% indicates normal air. The instrument is used to verify the space is safe for entry (O2 at the safe level) and to monitor the atmosphere during the work.

• Follow the company's safety and environmental protection policy and the SMS procedures.
• Report any unsafe condition, near miss, accident or non-conformity immediately to the responsible officer.
• Use the correct personal protective equipment (PPE) and follow the safe working practices (permits to work, lock-out/tag-out, enclosed space entry, hot work, etc.).
• Attend the required familiarisation, training and drills, and know the emergency duties (muster list, alarms, escape routes).
• Do not undertake any task for which you are not trained or authorised; ask for instructions if unsure.
• Maintain good housekeeping and keep the work areas safe and clean.
• Follow the instructions of the officers and the watchkeeping duties; report for duty on time and maintain the required rest.
• Protect the environment (no discharge of garbage/oil, follow the pollution-prevention procedures).
• Report any defect or damage to equipment immediately.