Explosion and fire in chemicals production plant

The accident occurred in the organo-metallic compound production unit, on a transport container for aluminium alkyls, which exploded during a cleansing process at the washing station. The incident was caused by a pressure build-up inside the container caused by flammable gases, mainly hydrogen, formed by the chemical reaction of aqueous caustic soda solution with the aluminium alkyl residues.

This cleansing of the transport containers is a standard procedure after return from customers and before a new filling. However, in this particular case, even after several attempts it was impossible to completely remove the deposits on the inner wall of the container. Tests aiming at the detection of reactive alkyl residues showed negative results. Thus, the deposits were exposed to an aqueous solution of caustic soda (NaOH). Since no production of heat or gases had been detected over a period of several hours, to increase the effectiveness of the cleaning procedure the container was sealed (against the instruction) and kept revolving around its longitudinal axis on a roller system.
After a short time of this process, the container burst, torn apart along the longitudinal axis, while part of is bottom was blown away and damaged a heptane pipeline. The released heptane ignited, and the whole building caught fire.
The container had been sealed infringing operating instructions.
The substances involved were aluminium, aluminium alkyls, heptane (H₃C₅CH₃), sodium hydroxide (NaOH), hydrogen.

The INITIATING cause was the pressure build-up inside the container by formation of flammable gases, mainly hydrogen.
The container had been tested for reactive material, as prescribed by the procedure.
However, the container had been sealed, against what prescribed by operating instructions. This could be the ROOT CAUSE, but it is impossible to determine if this was mainly a human error, or a lack of operative knowledge of the employees.

chemicals transport container, heptane pipeline

The event occurred after various failed attempts to perform the cleaning process according to instruction.

According to ARIA report, the injured persons were two.
According to ZEMA , only 1.
The material damage were assessed around 3,6 M de DM

The municipality safety department intervened with 49 fire trucks and 121 firefighters. They acted according to the strategy: “first control, then elimination”, and “"cooling and suppressing explosions, focusing on protection, and preventing spread", using equipment such as fire-fighting robots and mobile fire-fighting water cannons. The public security department dispatched 628 police officers to implement traffic control and maintain order at the scene. The health department dispatched 5 ambulances to stand by on site. Approximately 5 hours later, the fires were completely extinguished.

This is an accident where hydrogen was produced accidentally, by reaction of chemical product; therefore, in general, measures aiming at avoiding recurrence of the same type of accidents should concentrate in preventing formation of explosive atmospheres.

According to the sources (see References), the following measures were recommended:
(1) Cleaning operations of the containers to be performed with a washing medium not reacting with deposits in the containers;
(2) To provide the washing station with weighing systems, allowing a determination of residue quantities after washing by weighing the container before and after the cleaning process;
(3) To review of the operating instructions.
(4) To performing safety training activities.
(5) To develop accident scenarios and modelling their consequences;
(6) To review the emergency plans.