Case Study 3: Toxic Gas Poisoning in Manhole

Summary

Highlights

• A supervisor and his team were performing cable work in manholes when toxic gases struck. ⚠️
• Lack of ventilation led to hydrogen sulfide accumulation, causing three fatalities. 🚷
• The absence of a confined space permit and gas checks were critical oversights. ❌
• Improper rescue efforts highlighted the danger of unplanned actions. 🆘
• Key lessons are to ensure safety measures are in place before and during entry. 🛡️

Key Takeaways

• Always conduct risk assessments before entering confined spaces. 🛑
• Ensure proper mechanical ventilation is provided in enclosed areas. 🌬️
• Carry out thorough gas testing and monitoring. 🔍
• Never rush into a rescue without adequate preparation. 🚫
• Secure a valid confined space entry permit before commencing work. 📝

Overview

Chapters

• 00:00 - 00:30: Introduction In April 2000, a supervisor and his four workers began a cable-laying project involving four manholes at a worksite. Upon arrival, they opened manhole A to pump out the water, initiating their task.
• 00:30 - 01:00: Manhole B Incident After one and a half hours, the supervisor instructed workers 1 and 2 to open Manhole B, which was 20 meters away. Worker 1 retrieved a ladder from the lorry and placed it into Manhole B. He then climbed down until half of his body was inside. Simultaneously, worker 4 was in Manhole A, pushing copper cables over to Manhole B. Once the cable was transferred from Manhole A to B, the supervisor resumed his supervision.
• 01:00 - 02:00: Manhole C Incident In this chapter titled 'Manhole C Incident,' the supervisor instructed worker 1 and worker 3 to open Manhole C, which was located approximately 40 meters from Manhole A. As it was getting dark after 6 p.m., worker 1 went to retrieve a torchlight from the lorry, following the supervisor's instructions, and handed it to worker 3. The supervisor then directed worker 3 to examine the number of pipes visible in Manhole C.
• 02:00 - 02:30: Discovery of the Accident The chapter titled 'Discovery of the Accident' describes a sequence of events surrounding an accident at a worksite involving several workers and manholes. It begins with a supervisor leaving manhole C and heading back to manhole A. Worker 3 confirms the presence of six pipes in manhole C and goes over to inform the supervisor. Meanwhile, worker 1, waiting outside manhole C, notices a crowd gathering around manhole A. Curious, worker 1 approaches manhole A and finds three co-workers lying down, suggesting that an accident might have occurred.
• 02:30 - 03:30: Accident Analysis The chapter titled 'Accident Analysis' describes a tragic incident that occurred during a simple underground cable-laying job. It resulted in the loss of three lives. The narrative details how worker four was found at the farthest point inside the manhole, while the supervisor was discovered lying on top of worker three. The analysis highlights critical failures, notably the lack of proper ventilation and insufficient preparation prior to commencing the job. These oversights contributed to the accident.
• 03:30 - 05:30: Lessons Learned The chapter titled 'Lessons Learned' discusses the events leading to a workplace accident due to lack of safety measures in handling manholes. It highlights that the manholes were not properly ventilated, leading to the accumulation of toxic gases. A significant focus is on hydrogen sulfide gas, which was released during the work due to water containing sludge. The chapter emphasizes the absence of preventive measures, such as mechanical ventilation or proper entry permits, that could have avoided the mishap.

Case Study 3: Toxic Gas Poisoning in Manhole Transcription

• 00:00 - 00:30 in April 2000 a supervisor and his four workers were engaged to perform cable-laying work involving four manholes at a worksite upon arrival the workers opened manhole a and proceeded to pump water out
• 00:30 - 01:00 after one and a half hours the supervisor instructed worker 1 and 2 to open manhole B which was 20 meters away worker 1 went to the lorry to get a ladder which he then placed into mantle be he climbed down the ladder until half his body was inside manhole B at the same time worker for was inside manhole a pushing copper cables over to man ho B after the cable was pulled over from manhole a to be the supervisor
• 01:00 - 01:30 instructed worker 1 and 3 to open manhole sea which was about 40 meters from manhole a it was now after 6 p.m. and the sky was starting to get dark worker 1 went to get a torch light from the lorry and handed it over to worker 3 as instructed by the supervisor the supervisor instructed worker 3 to check the number of pipes in sight manhole see
• 01:30 - 02:00 the supervisor then left manhole sea and headed back to manhole a worker 3 checked and confirmed that there were 6 pipes in manhole sea he then went over to manhole a to inform the supervisor 15 minutes later worker 1 who was waiting outside manhole sea noticed that a crowd had gathered around manhole a worker 1 went over to manhole a and saw three of his co-workers lying
• 02:00 - 02:30 motionless inside the manhole he noticed that worker four was the farthest away inside the manhole the supervisor was found lying on top of worker three a simple cable laying job resulted in the loss of three lives what went wrong lack of ventilation no preparations were made prior to the underground cable laying
• 02:30 - 03:00 work the manholes were only opened on the day of accident mechanical ventilation was not used to supply fresh air into the manholes accumulation of toxic gases when worker four was carrying out work in the manhole hydrogen sulfide gas was released to due to the agitation of water containing sludge hydrogen sulfide was allowed to accumulate too due to lack of insulation after opening and during work in the manhole no permit for entry no one had
• 03:00 - 03:30 applied for a confined space entry permit and gas checks were not conducted to determine the level of oxygen flammable gases and hydrogen sulfide prior to entering the manhole lack of emergency response procedures the workers entering the manhole were not equipped with a full body harness and a lifeline and there was no confined space at Hedlund assigned to keep watch outside the manhole lessons learned
• 03:30 - 04:00 risk assessment risk assessments must always be conducted before starting work in a confined space appropriate risk control measures should be put in place before manhole entry is attempted mechanical ventilation before entry into the manhole it is crucial to purge the space adequately to remove hazardous contaminants subsequently continuous
• 04:00 - 04:30 ventilation should be provided to maintain a safe work environment gas testing and monitoring of the manhole atmosphere the manhole atmosphere must be tested by a confined space safety Assessor workers can enter a manhole only if it is certified safe for entry workers should also be equipped with a personal gas detector to continuously monitor the atmosphere after entry into the manhole confined space entry permit
• 04:30 - 05:00 system supervisors and workers must also ensure that the entry permit is valid correctly endorsed and that all the necessary gas checks have been carried out before entering the confined space emergency response plan supervisors and workers should be reminded of the importance of following proper emergency response procedures and not to be rash when attempting rescue in a confined space in this case worker 3 he was overcome by hydrogen sulfide when he
• 05:00 - 05:30 rushed into the manhole to rescue worker 4 similarly the supervisor was overcome 1 when he rushed into rescue worker 3 and worker 4 important lesson learnt is that one should not rush into an unknown atmosphere without being suitably prepared this is because an unplanned rescue may result in multiple fatalities remember an unplanned rescue may be your last