M2642 - Near Miss - Potential Poisoning and Asphyxiation
Initial Report
I was on a vessel during an extensive refit and was responsible for cleaning and painting the engine room bilges. The main bilge sump was 6 ft deep, just enough to crouch in, and I was at the bottom, using acetone to degrease the surfaces in preparation for painting. Unbeknownst to anyone in the crew, acetone expands to over 300% of its original volume and is heavier than air. As a result, oxygen was rapidly displaced, and the vapour had nowhere to escape. I was wearing a VOC (Volatile Organic Compound) mask, in line with the company’s operating procedures, so I had no way to sense what was happening. I didn’t have a ventilation system set up, a body-worn gas detector, or a lookout posted. The first sign of trouble was not light-headedness or nausea, but a deep sense of ‘fight or flight’ in my chest. I scrambled out of the bilge sump and just caught my breath enough to call on the radio. Luckily, I escaped without needing medical treatment, but it could have been much worse. It’s a lesson I’ve carried throughout my career.
CHIRP Comment
Bilges are enclosed spaces as defined in the Code of Safe Working Practices Section 15, MGN 659, and MSC A.1050(27). Vessels should clearly identify and record which compartments onboard are considered enclosed spaces (ES), or confined spaces (CS) and ensure this information is reflected in the SMS and risk assessments. While the reporter was following the vessel’s SMS, the VOC mask used was not suitable for the hazard encountered.
This report highlights an important and often under-appreciated chemical hazard associated with routine tasks such as bilge cleaning. The reporter was working during a refit period, when ventilation arrangements and system configurations may differ from normal operations. The use of acetone in the confined geometry of a bilge sump, combined with poor ventilation and no atmospheric monitoring, created a potentially life-threatening situation. A personal oxygen meter should be worn. It is commendable that the reporter recognised the symptoms early and exited the space promptly, thereby preventing a more serious outcome.
A key learning point is that many common solvents produce vapours that can rapidly displace oxygen because they have higher vapour densities, particularly in enclosed, confined, and poorly ventilated spaces. VOC masks protect against the inhalation of certain substances but do not provide notification that oxygen depletion is occurring. Carrying gas-detection equipment is essential, not only for formally designated enclosed spaces or confined spaces but also when using oxygen-displacing chemicals in any restricted area.
Task risk assessments should explicitly consider the chemical properties of substances used, as documented in their safety data sheets, including their vapour behaviour, ventilation arrangements, and the need for atmospheric monitoring. Standard enclosed-space precautions, including portable gas detectors, effective mechanical ventilation, and a designated standby person, should always be applied. This is particularly important during refit or maintenance periods, when resources can be reduced due to additional workload.
This report also underlines the importance of crews having access to and understanding Safety Data Sheets (SDS) in the correct working language. Pre-task planning should ensure that all personnel are aware of the risks of vapour expansion and oxygen displacement, as well as the limitations of PPE.
CHIRP strongly recommends that solvent-based cleaners, such as acetone, should not be used for bilge cleaning.
Key Issues relating to this report
Safety Culture – The organisation had not fully identified or communicated the atmospheric risks linked to solvent cleaning during refits.
Capability – The task lacked a specific assessment that considered chemical behaviour, confined space characteristics, and required controls. Knowledge of solvent-related oxygen displacement was not part of regular training or toolbox talks.
Communication – The crewmember was isolated from the other crew, so no communication could take place.
Teamwork – No designated standby person or two-way check-in process for potentially hazardous work. The crewmember was working independently without support.
Design and engineering control – Lack of integrated ventilation/gas detection for small, confined compartments.
Local Practice – Procedures and work-as-done did not align with the real risks and relied heavily on PPE rather than higher-order controls.
Key Takeaways
You can’t smell missing oxygen—so plan for the hazard you can’t sense.
Regulators – This report reinforces the need to ensure that guidance on confined-space entry and hazardous-substance use, explicitly covers the oxygen-displacement risks of common solvents such as acetone. Regulatory frameworks may already mandate atmospheric testing and ventilation for enclosed-space work, but this incident shows how everyday maintenance tasks can fall outside formal definitions while presenting identical hazards. Clearer expectations around gas detection, task-specific risk assessments and solvent-handling protocols during refit periods would help close this gap.
Managers – The key takeaway is that work planning must account for both the environment and the chemical properties of the substances being used. Procedures that rely solely on PPE, without ventilation or atmospheric monitoring, create a false sense of security. Ensuring that Safety Data Sheets are incorporated into pre-task briefings, making gas detectors readily available and verifying that confined-space precautions are applied, even in small spaces like bilge sumps, are essential steps. Refit periods require heightened vigilance because non-routine work often involves equipment isolation, restricted access and chemical hazards that may not be part of everyday operations.
Crew – The lesson is that familiarity with a product does not guarantee safety. Solvents can behave unpredictably in confined areas, and symptoms of oxygen depletion may be subtle until they become dangerous. Relying on PPE alone is not enough; ventilation, monitoring and having someone aware of the task are critical safeguards. Trusting instinct and acting early, as the reporter did, can prevent severe outcomes.