In a non-hazardous waste incineration plant at about 1:30 p.m., a fire broke out in the lower level of the furnace’s domestic waste feed hopper, near the hopper’s actuating cylinders.

A pressure drop alarm on the hydraulic system was triggered and alerted the shift manager. Staff then called the fire brigade and began fighting the fire with hoses and fire extinguishers until they arrived. The fire was contained at around 2:30 p.m.

Consequences

The fire caused only property damage, but the incineration line was shut down for damage assessment and safety checks. The line was put back into service 2 days later. The extinguishing water was collected from the site’s wastewater network and directed to the internal treatment plant for processing.

Causal analysis

It was determined that the cause of the fire was a leak in the hydraulic oil supply piping of the hopper cylinders used to push the waste into the furnace. For example, a mounting plate on one of the cylinders broke causing a weld on the supply line to rupture, leading to a purge of the system. The oil leaked out and spilled into a retention area which then overflowed. The oil then ignited upon coming in to contact with the hot walls of the furnace.

Measures taken

Following the accident, the operator:

• repaired the ruptured weld, replaced the fittings and hoses, and added reinforcement screws to secure the cylinder mount;
• checked all other cylinders, piping, fixing plates and welds throughout the installation. The installation had 3 other hydraulic cylinders similar to the one that had failed;
• replaced the hydraulic fluids hitherto used with less flammable fluids;
• installed a system to ensure more efficient collection of any leaks from the hydraulic system: installation of a pipe to evacuate the oils collected in the retention tank under the cylinders to a larger retention tank. Before conducting this work, the technician filled the existing retention tank with an absorbent material to limit an overflow if oil is present.