A power outage occurred in the ammunition loading workshop of a weapons factory working with TNT-based cast explosives. The power failure caused the loading tank’s heating system to shut down and resulted in solidification of a portion of the explosive in the tank (solidification temperature: 80 °C). While the TNT was still hot enough for casting, the crew on duty attempted to quickly empty the tank via the distributor block by filling aluminium trays present in the workshop. This practice is normally used for emptying the bottom of the tank at the end of the day and is explained in the occupational safety study. Four hundred kilograms of TNT had solidified in the tank and the distributor block. Activities in the area were stopped.

The general power outage in the area was due to a cable break in the electrical cabinet of the Low Voltage Switchboard. According to the expert’s report, the fault was caused by excessive humidity inside the electrical cabinet. As the power failure occurred inside the electrical cabinet (it was not a power failure caused by the electrical utility), the generator in the area did not have to be started.

The cabinet was repaired and the hot water and steam generating systems were checked and restarted. A faulty valve on the cleaning water system was replaced.

After securing the system (disconnection of the electrical and pneumatic power supplies to prevent any movement during this operation), repairing the equipment, and restoring the power, the solidified block of TNT was remelted on May 2. As the tank was not designed for melting the product (but simply to maintain it at a controlled temperature near the melting/solidification point), the operation took an entire day to complete. The tank was finally emptied at 5:30 p.m. The explosive was divided into containers to be re-solidified into 3-kg ingots. The ingots of explosive, which were mainly uncontaminated by water, were recycled for subsequent production. The polluted ingots were disposed of in the site’s pyrotechnic burning area.

Blast casting activities were then resumed in mid-February following:

• improvement of repaired electrical cabinet’s environment (installation of a ventilation system in the cabinet and complete drying, drying of the cable tunnels in the technical room),
• general verification of the process installations and products in the impacted area (check that the tank’s mixer blades, tank closing valve, and the dosing unit’s distributor are operating nominally, etc.),
• verification of the zone’s genset (start-up test, replacement of old fuel to increase its reliability, etc.),
• search for the source of an insulation fault in the zone’s electrical installation and correction of the fault.

A new electrical cabinet was ordered based on new specifications allowing for better segregation of functions and for maintaining the safety of critical equipment.

The equipment to be backed in the event of an electrical cabinet failure is identified. In particular, water and steam power must be maintained long enough to allow the tank to be completely emptied before the explosive solidifies.

A procedure to empty the tank quickly in the event of a power loss was drawn up.