Fire at a generator of a power plant

This incident occurred during maintenance works after an outage at a turbine and generator unit of the plant. At the time of the incident, 15 maintenance technicians had already been working on the unit since more than 10 days.
An access cover was removed causing the release of hydrogen and resulting in multiple explosions and fires. The explosion was heard 35 miles away. The blast tore a huge section from a building holding the six coal-fired generators of the plant and caused three fatalities and several injuries.
The hydrogen was used as cooler of the unit. The hydrogen system should have been depressurised and purged before its opening, because the workers assumed that these operations had already been done before (they are usually performed in the 2-3 first days of a maintenance intervention).

INITIATING CAUSE was the accidental release and ignition of hydrogen used for the cooling of the turbine and generator unit.

The release was due to the failing of following the safe procedure, what brings to the following ROOT CAUSES:
(i) lack of or shortcoming in supervision of the maintenance work, which could reveal Inadequate process safety management,
(ii) lack of or shortcoming in communication between maintenance contractors and plant personnel,
(iii) lack of or shortcoming in regulatory oversight (according to the ICHEME source, there have been no plant audit despite several leaks, fires and explosions since 1992).

turbine and generator unit, hydrogen-based cooling system, coal-fired generator

Maintenance works were ongoing after an outage at a turbine and generator unit of the plant. It was a 375 MW unit, part of a coal-fired power station.

At the time of the incident, maintenance technicians had already been working on the unit since more than 10 days.

According to the ICHEME source, there have been no plant audit despite several leaks, fires and explosions since 1992.

Three fatalities and several injuries were the consequences. The number of injuries varies from 15 to 50 depending on the report (OHSA report states 15).
Amyotte reported 38 evacuated.
Only 1 of the 6 turbo- generator sets in the turbine hall was damaged. Also the building was severely damaged. The explosion was heard 35 miles away.
The US$ 5 million of damage is based only on the costs of fuel replacement and power purchase.

OSHA gave the company the a serious violation citation and a penalty of 25000 $,

The depressurisation and purging of a hydrogen system is the most fundamental measure preventing incidents. To ensure that this occurs every time, the following is needed :
(i) Adequate safety procedures for maintenance must be in place and enforced by means of supervision.
(ii) Plant operators must supervise the maintenance team and guarantee coordination between the contractors and the plant workers. For example, the maintenance team must be briefed accurately before starting the works.
(iii) The status of machinery, components and subcomponents must be communicated hydraulic, pneumatic, mechanical, electrical and other utilities. This has to be updated and changes have to be communicated along the progress of maintenance process.