The tank decides the risk
OSHA 1910.252 bars hot work on used drums, barrels, or tanks until they are cleaned so thoroughly that no flammable material or residue remains, and lines connected to the vessel must be disconnected or blanked. The OSHA oil and gas eTool points at the exact equipment that fails this test on a lease: production tanks, vacuum trucks, frac tanks, flowback tanks, and produced water tanks, all of which can hold hydrocarbon vapors in the headspace long after they look empty.
The fire watch is a job, not a body
A fire watch is required whenever welding or cutting happens where other than a minor fire might develop. The watch must have extinguishing equipment, know how to use it, know the alarm system, and stay at least 30 minutes after the work ends to catch smoldering fires. When combustibles sit behind a metal wall or partition, a second watch is needed on the opposite side because heat conducts through the steel.
The permit makes it deliberate
API RP 2009, updated in 2022, is the industry practice for safe welding, cutting, and hot work in petroleum facilities, and it pairs with the permit system the OSHA eTool describes for areas where flammable atmospheres could exist. Combustibles are cleared or protected within the work radius, drains and openings are sealed, and gas testing confirms the atmosphere before ignition. A permit that is rubber-stamped is theatre. A permit tied to gas test results is a control.
Hot work shares its life-critical habits with lockout/tagout, confined space entry, and job safety analysis. Each one stands on a dated, verifiable record. If the permit and the fire watch log are filled in after the fact, an operations audit will show which welds actually followed the sequence.