A welder is tasked with welding inside a large, enclosed vessel that has an opening of 800 mm diameter. The vessel was previously used to store a non-flammable, non-toxic liquid. Before entry, atmospheric testing confirms acceptable oxygen levels, and no hazardous gases are present. Despite these readings, what essential safety measure must be rigorously maintained during welding operations within the vessel?

Question: A welder is tasked with welding inside a large, enclosed vessel that has an opening of 800 mm diameter. The vessel was previously used to store a non-flammable, non-toxic liquid. Before entry, atmospheric testing confirms acceptable oxygen levels, and no hazardous gases are present. Despite these readings, what essential safety measure must be rigorously maintained during welding operations within the vessel?

Answer options:

• Continuous ambient air monitoring for combustible gases.
• Implementation of a positive pressure ventilation system. ✅ A dedicated attendant stationed outside and continuous communication.
• Requirement for a full-face respirator with supplied air.

Correct answer: A dedicated attendant stationed outside and continuous communication.

Explanation: Even if the atmosphere appears benign initially, an enclosed space like a vessel is by definition a confined space. A dedicated attendant outside ensures a rescue plan is immediately actionable, and continuous communication allows for monitoring the welder's well-being and immediate response to any changes within the space or to the welder. While ventilation is important, the human element of an attendant is critical for confined space safety. Monitoring for combustible gases is important if flammables were present, but the question states it was non-flammable.