Hot Work Adjacent to a Tank Being Cleaned
A tank that last contained crude oil is being cleaned. Workers inside are using hand tools to remove scale; the atmosphere currently reads 0% LEL with continuous ventilation. Simultaneously, a contractor wants to perform welding on a pipe support located 8 m from the tank's shell manway, on the same concrete pad. The tank has been isolated and steamed, but the floating roof seal area and the sludge at the bottom have not been fully cleaned. Wind is light and variable. The welding contractor argues the tank reads 0% LEL so there is no hazard. The cleaning crew inside is not aware of the welding. The entry supervisor for the tank and the welding supervisor have not coordinated.
1. Identify the hazards created by simultaneous cleaning and hot work and the coordination failures.
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Hazards: hot work near a tank containing residual hydrocarbons (sludge, seal area) can ignite flammable vapors released by cleaning activities or present in the tank. Cleaning disturbance can liberate vapors that migrate to the hot work. The 0% LEL reading is a single point in time and does not cover the seal area or sludge, and light variable wind makes dispersion unpredictable. There is also a risk that hot work sparks or slag reach the tank area.
The coordination failure is serious: the two supervisors have not communicated, the cleaning crew is unaware of welding, and no combined permit or hazard review exists. Simultaneous operations require a joint assessment, defined exclusion zones, and a single point of control for ignition sources.
2. Recommend the controls and decision for proceeding.
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Do not allow hot work until a joint review is completed. Controls: establish a hot work permit coordinated with the tank entry permit; define and enforce an exclusion zone around the hot work and the tank manways; verify atmospheric conditions at both locations with calibrated monitors; ensure the tank's residual hydrocarbons are characterized and that cleaning activities will not release flammable vapors during hot work. Consider sequencing operations (stop cleaning during hot work or vice versa). Notify the cleaning crew and brief both teams. Assign a fire watch for hot work. If conditions cannot be verified or coordinated, hot work should be postponed.