Case Study 3: Toxic Gas Poisoning in Manhole

Summary

In April 2000, a fatal accident occurred during a cable-laying operation involving multiple workers and manholes. Due to a lack of ventilation, failure to conduct gas checks, and absence of a confined space entry permit, hydrogen sulfide gas accumulated in the manholes, leading to the deaths of three workers. An unplanned rescue attempt by the supervisor and workers only worsened the situation. The incident highlights critical safety failures, emphasizing the importance of risk assessments, ventilation, gas monitoring, and emergency response procedures in confined space work.

Takeaways

• 😀 Proper risk assessment is essential before starting any confined space work.
• 😀 Adequate ventilation is crucial to prevent the buildup of toxic gases like hydrogen sulfide.
• 😀 Mechanical ventilation should be used to purge confined spaces before entry.
• 😀 Gas testing and continuous monitoring are necessary to ensure a safe atmosphere in manholes.
• 😀 A confined space entry permit is mandatory and must be valid before any work starts.
• 😀 Workers must be equipped with personal gas detectors to monitor hazardous gases in real-time.
• 😀 Supervisors must ensure that all gas checks are conducted before entry into confined spaces.
• 😀 Emergency response procedures should be in place, and workers should not attempt unplanned rescues.
• 😀 Full-body harnesses and lifelines are necessary for workers entering confined spaces.
• 😀 Rushing into a dangerous environment without proper preparation can lead to multiple fatalities.

Q & A

What was the nature of the work that the workers were engaged in?

The workers were performing cable-laying work involving four manholes at a worksite.

What were the immediate actions taken by the workers upon arrival at the worksite?

Upon arrival, the workers opened manhole A and proceeded to pump out water from the manhole.

How long did it take for the workers to pump out the water from manhole A?

It took the workers about one and a half hours to pump out the water from manhole A.

What mistake did the workers make when opening manhole B?

Worker 1 placed a ladder into manhole B and climbed down, leaving half of his body inside the manhole while other workers were still working in manhole A.

What crucial safety step was missing when the workers moved between manholes?

The workers did not conduct any gas testing or safety checks before entering the manholes, leaving them exposed to hazardous gases like hydrogen sulfide.

What hazardous gas was released during the work in the manholes?

Hydrogen sulfide gas was released due to the agitation of water containing sludge when worker 4 was carrying out work in manhole A.

What key safety equipment was missing for the workers entering the manholes?

The workers were not equipped with full-body harnesses or lifelines, which are essential for safety in confined spaces.

Why was the supervisor and other workers exposed to danger after the initial accident?

The supervisor and other workers rushed into the manhole to perform rescues without considering the dangers of the unknown atmosphere, leading to multiple fatalities.

What were the key failures that led to the tragic accident?

The key failures included lack of ventilation, no pre-work safety checks, absence of a confined space entry permit, and no emergency response procedures or monitoring outside the manhole.

What lessons should be learned from this incident to prevent similar accidents?

Key lessons include conducting thorough risk assessments, ensuring mechanical ventilation, performing gas testing, using proper safety gear, and having an emergency response plan in place before entering confined spaces.