A plumber is performing a repair inside a large industrial tank that has been cleaned and gas-freed. An atmospheric monitor worn by the worker alarms, indicating an oxygen level of 18.5%. What is the immediate action required by the plumber and the attendant?

Question: A plumber is performing a repair inside a large industrial tank that has been cleaned and gas-freed. An atmospheric monitor worn by the worker alarms, indicating an oxygen level of 18.5%. What is the immediate action required by the plumber and the attendant?

Answer options:

• The plumber should continue working until the oxygen level drops below 16%
• The attendant should notify a supervisor, and the plumber should continue to monitor the situation ✅ The plumber must immediately exit the tank, and the attendant should initiate emergency procedures
• The attendant should try to ventilate the tank further before the plumber exits

Correct answer: The plumber must immediately exit the tank, and the attendant should initiate emergency procedures

Explanation: An oxygen level of 18.5% is below the acceptable minimum of 19.5% for confined space entry. Upon an alarm, the plumber must immediately exit the tank, and the attendant should initiate emergency procedures as per the confined space entry plan, as continuing to work or re-ventilating with the worker inside is unsafe.