Case Study 3: Toxic Gas Poisoning in Manhole

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 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 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 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 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 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 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 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 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 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 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

Channel: Workplace Safety and Health Council

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Id: yJZcbSa3DFE

Length: 5min 29sec (329 seconds)

Published: Fri Dec 05 2014