A plumber must perform maintenance inside a large, underground storm sewer pipe. Before entry, an atmospheric test reveals 18.5% oxygen, 0.5% carbon monoxide, and 25 ppm hydrogen sulphide. The company's confined space plan indicates entry is permissible once oxygen levels are between 19.5% and 23.5% and all hazardous gas levels are below permissible exposure limits (PELs). What is the correct next step?

Question: A plumber must perform maintenance inside a large, underground storm sewer pipe. Before entry, an atmospheric test reveals 18.5% oxygen, 0.5% carbon monoxide, and 25 ppm hydrogen sulphide. The company's confined space plan indicates entry is permissible once oxygen levels are between 19.5% and 23.5% and all hazardous gas levels are below permissible exposure limits (PELs). What is the correct next step?

Answer options: ✅ Initiate forced air ventilation to improve oxygen levels and reduce hazardous gas concentrations, then retest.

• Put on an air-purifying respirator and enter quickly to perform the task.
• Install a lockout/tagout on the sewer system and proceed with the entry.
• Determine the source of the hazardous gases before proceeding with any ventilation.

Correct answer: Initiate forced air ventilation to improve oxygen levels and reduce hazardous gas concentrations, then retest.

Explanation: The atmospheric test reveals an oxygen-deficient atmosphere (18.5% is below the acceptable range) and dangerous levels of carbon monoxide and hydrogen sulphide (0.5% CO is 5000 ppm, far exceeding PELs, and 25 ppm H2S is also unsafe). The immediate and correct action is to ventilate the space to bring the atmosphere within safe limits, then retest before considering entry. Entering with an air-purifying respirator is insufficient for these conditions, and lockout/tagout does not address atmospheric hazards.