On a Saturday at 3 pm, fire broke out inside a 100-m² workshop of a chemical complex. The workshop was connected to a production unit for hydrazine by-products, where compositions were based on AZDN and 0.5% to 1% silica. Heat-sensitive AZDN decomposes, at temperatures > 50°C, into gaseous substances: nitrogen (N2), flammable TMSN (whose combustion generates N2, water vapour and CO2), along with a small quantity of unburned toxins (including TMSN, carbon monoxide (CO) and hydrocyanic acid (HCN)). As the only on-site facility using dry AZDN, this workshop also housed an N2 mixer (dust explosions), a vibrating sieve and handling machinery for barrels containing raw materials or compounds. A centralised suction system for device sanitisation, equipped with a cyclone and bag filter, plus an exhauster to clean the equipment and floors, were set up outside the building. A technician was cleaning the exhauster receptacle at the beginning of his shift and launched production of 3 pallets of AZDN compound. As of the 3rd pallet, 100 to 200 g of AZDN overflowed and spilled onto the floor. The technician suctioned the room and the top of the sieve shaker for 5 to 7 min, removed an empty barrel from the building and noticed smoke and small flames above the exhauster. He deployed a fire hose and asked a fellow technician to notify the shift boss. 30 s after sprinkling began in the zone, a blast with sudden ignition occurred within the sanitisation suction system. Black smoke surrounded both technicians, who move away quickly. The shift boss activated the water curtains; in-house fire-fighters controlled the blaze within 10 min. The exhauster motor contactor had caused the fire. The heat released by the ignited exhauster heated the filter bags containing 20 to 30 kg of AZDN, whose decomposition gases subsequently ignited. Hospitalised for a few hours, the 2 technicians sustained respiratory irritations and received oxygen therapy treatment; their blood analyses did not reveal any CO / HCN intoxication. The damaged exhauster and suction system (€30,000), whose installation was overhauled to avoid fire propagation, were both modified by: eliminating all electrical contact with the outside; improving the ADF motor, filter and receptacle to avoid overflow; and facilitating handling. Technicians were reminded of operating guidelines (especially how to respond to an AZDN fire).
