Hot work and flammable atmosphere testing
Hot work and flammable atmosphere testing
This domain tests the additional controls for welding, cutting, grinding and other ignition sources.
Core rules
- Hot work permit is required in hazardous areas and near confined spaces. The AGT tests for flammable gas before the permit is issued and at intervals during the work.
- Criteria: hot work generally requires 0% LEL at the work site and in surrounding areas, because any flammable atmosphere can be ignited. Some site standards use a low threshold, but 0% LEL is the safe default and is common offshore. Entry for cold work may allow up to 10% LEL; hot work does not.
- Test the right places: the hot work point, inside vessels and pipes, low points, drains, trenches and adjacent areas where heavier-than-air gas can travel. A reading at the welder's hand is not enough.
- Isolation and purging: isolate and blank fuel lines; purge vessels of flammable product; do not hot work inside an inerted vessel - the atmosphere is oxygen-deficient and the permit should prohibit it.
- Continuous monitoring and fire watch: keep a flammable gas monitor running, assign a fire watch, provide extinguishing equipment and stop work if the reading rises or the alarm sounds.
- Ignition control: ATEX-rated equipment, bonding and grounding, non-sparking tools, screens and barriers.
Worked example
Welding is planned on a pipe rack next to a drain. The LEL reading at the work point is 0%, but the drain reads 8% LEL. Reasoning: heavier hydrocarbon vapour has migrated along the drain and can reach the hot work. Work must stop until the drain is isolated, purged and re-tested, and the permit must record the additional control.
Traps
Testing only the hot work point; using a methane-calibrated LEL meter on a heavier hydrocarbon without a response factor; restarting after a break without re-testing; allowing hot work in an inerted space; relying on a fire extinguisher instead of a fire watch and monitoring.