Solvent Odor and Ventilation in a Confined Space Coating Job
A crew is applying a solvent-borne epoxy inside a 3 m diameter steel vessel through a single 500 mm manway. A blower is running, but the flexible duct discharges near the manway rather than at the bottom of the vessel, and the vessel is only partially purged. After 40 minutes, two workers report headache and dizziness. The entry permit lists the atmosphere as tested before entry, and a gas monitor is clipped to one worker's belt but has not been calibrated in three months. The coating contains xylene and the safety data sheet lists it as flammable with a flash point around 25–30 °C.
1. Identify the safety failures in this setup and state the immediate action.
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Immediate action: evacuate all workers from the vessel, account for everyone, and do not re-enter until the atmosphere is re-tested and the ventilation is corrected. Treat the headache and dizziness as a possible exposure event and get medical evaluation.
Failures: (1) ventilation is misdirected - supply should deliver fresh air to the breathing zone and exhaust should draw from the low point where heavier solvent vapor accumulates, not discharge at the manway; (2) the vessel is only partially purged, so vapor can build; (3) the gas monitor is out of calibration (three months), so its readings cannot be trusted; (4) a single pre-entry test does not cover a changing atmosphere during coating; (5) the solvent is flammable with a flash point in the range of ambient conditions, so ignition control and bonding/grounding must be confirmed; (6) the permit and entry plan did not account for continuous monitoring and forced ventilation during application.
2. Describe the controls you would require before work resumes, including monitoring and ignition control.
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Controls before resuming: recalibrate or replace the gas monitor and use it for continuous monitoring with alarm setpoints for the solvent and oxygen; position supply air at the bottom and exhaust at the top (or per the vapor density of the solvent - xylene vapor is heavier than air, so exhaust low and supply to the breathing zone) to achieve effective purge and dilution; verify ventilation airflow before entry and keep it running throughout; confirm bonding and grounding of the vessel and spray equipment and eliminate ignition sources given the flammable solvent; require appropriate respiratory protection based on measured exposure and the SDS; limit entry time and use an attendant with communication; re-test the atmosphere before each entry and whenever conditions change; update the permit to reflect continuous monitoring and ventilation during coating. Document all of it.