A welder is asked to cut a steel pipe that has been in service carrying natural gas. The pipe has been purged with nitrogen for an hour, but the welder is concerned about residual gas and potential ignition. What crucial step must be verified before any hot work begins on this pipe?

Question: A welder is asked to cut a steel pipe that has been in service carrying natural gas. The pipe has been purged with nitrogen for an hour, but the welder is concerned about residual gas and potential ignition. What crucial step must be verified before any hot work begins on this pipe?

Answer options:

• The welder's certification for natural gas line work.
• The availability of a high-pressure oxygen bottle for enriched air. ✅ Atmospheric testing has confirmed zero readings for flammable gases and vapours.
• The pipe has been painted with fire-retardant coating.

Correct answer: Atmospheric testing has confirmed zero readings for flammable gases and vapours.

Explanation: When working on pipes that have contained flammable substances, thorough atmospheric testing is paramount to confirm the absence of any flammable gases or vapours, even after purging. This ensures the environment is safe for hot work and prevents explosions. Welder certification and fire-retardant coating are important but do not directly address the immediate risk of an explosion from residual natural gas. Enriched oxygen would be highly dangerous.