An operator is scheduled to perform maintenance inside a large storage tank that contained non-toxic grain, but has been empty for several weeks. Entry is through a top manhole. What is the most critical hazard to consider initially for this confined space entry?

Question: An operator is scheduled to perform maintenance inside a large storage tank that contained non-toxic grain, but has been empty for several weeks. Entry is through a top manhole. What is the most critical hazard to consider initially for this confined space entry?

Answer options: ✅ Oxygen deficiency or enrichment due to decomposition or material residue.

• Chemical burns from residual grain dust.
• Falling objects from the manhole access.
• Excessive noise levels within the tank.

Correct answer: Oxygen deficiency or enrichment due to decomposition or material residue.

Explanation: Even with non-toxic materials like grain, decomposition can consume oxygen or produce CO2, leading to oxygen deficiency. Furthermore, grain can spontaneously combust if conditions are right, leading to oxygen enrichment. Therefore, atmospheric testing for oxygen levels is a critical first step for this confined space entry according to CSA Z1006-16.