Case study Two fatalities in a toxic cloud Frank Verschueren Process Safety Inspector Belgium Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/2015 1

Very short abstract During a shutdown the evaporator for crude titanium tetrachloride (TiCl4) overflowed. On contact with humidity TiCl4 reacted forming a cloud of very fine TiO2 particles and very toxic gaseous HCl. Two employees of a contractor firm working nearby were lost in the cloud of gas and died as a result of HCl intoxication. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/2015 2

Report of events (1) The night before the accident the production unit was shut down an annual maintenance turnaround. One of the tasks the cleaning and recalibration of a level sensor at the top of a TiCl4 evaporator A maintenance employee of the company was working together with a contractor on this level measurement at the top floor of the TiCl4 evaporator. The team supervisor had only orally released the work on the measurement level of the evaporator after verification of the pressure in the evaporator. Although a work permit had been written for this work the work permit was not used. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/2015 3

Installation Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/ Level sensor Level senor TiCl4 evaporator Level senor crudeTiCl4 vessel Level senor Independent level sensor with alarm Level senor Controlled valve Level senor Manual valve

Report of events (2) The only protection of the workers from exposure to TiCl4 or HCl fumes was the aspiration of these vapours at the top of the evaporator through the central suction system. Further measures had been put in place to avoid a blocking by solid impurities present in the crude TiCl4. - Therefor the evaporator was not emptied for the work on the instruments on top of it. - The circulation pump for crude TiCl4 was not shut down to avoid blocking elsewhere in the crude TiCl4 system by settling of particles. All this was described in the prepared work permit. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/2015 5

Report of events (3) Before starting to work on the level sensor the signal cable of the level measurement had to be disconnected. By doing this this there was no more signal input of the level measurement to the process computer. Unfortunately this was interpreted by the process computer as if the real level in the evaporator was zero and the evaporator had run empty. Since the evaporator level was automatically controlled at a certain threshold, the process control system opened the control valve to feed new TiCl 4 into the evaporator. To avoid blocking elsewhere in the crude TiCl4 system the circulation pump for crude TiCl4 was not shut down and also for the same reason the manual inlet valve of the evaporator was not closed. Consequently the filling of the evaporator continued. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/2015 6

Installation : components of filling Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/ Circulation pump Manual Valve Signal Cable Level senor Controlled valve

Report of events (4) After having disconnected the signal cable, the technician loosened the flange which connected the level measurement on the evaporator. After the removal of the flange, the vacuum in the evaporator was verified, and the vacuum was considered to be not high enough. Therefor the work to the level measurement was interrupted and the maintenance technician went to the control room to ask for more suction. Shortly after this the evaporator overflowed through the open flange of the level measurement on the second floor of the building. Hereby an estimated 7.5 tonnes of TiCl4 was released in the production building. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/2015 8

Report of events (5) The released TiCl4 reacted strongly with the humidity in the air so immediately a cloud of HCl and TiO2 was formed. HCl is a toxic and highly corrosive gas while TiO2 is a white pigment so a white opaque and very toxic cloud with almost no visibility was produced. Because the evaporator shell is extending from the ground floor to the second floor of the building (through the necessary floor passages) the TiCl4 and this resulting blinding and toxic cloud of HCl and TiO2 could spread throughout the building. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/2015 9

Report of events (6) Just outside the building on an external platform connected with the first floor there were three other employees of a contractor firm working. There was no permanent presence of an employee of the site company. The normal access to their workplace was through the building. These 3 contractor people had always been employed by the contractor firm in their mechanical repair shop and were not used to work in process installations and so they were for the first time working in this company. As they had arrived late that day at the site, they had missed the safety briefing. Moreover at the start of the work they were not pointed out the exact evacuation routes so that they were not aware of the presence of an alternative escape route out of the building via a flight stairs a little further from the floor where they worked. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/

Report of events (7) The outlet of a wall fan for room ventilation was immediately near their work platform. Fumes coming out of this wall fan gave them an alert. So they put on a full face mask with filter (provided by the company) and tried to evacuate. Unfortunately they tried to evacuate through the building. They tried to reach the staircase through which they had come. The leak and the deadly cloud however was just between their workstation and the stairs. In the building the two victims entered the white cloud and were completely blinded by it. As such they were not able to find the exit in time. The third contractor was on a different place and managed to escape via another escape route. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/

Report of events (8) On the information of the third contractor, some people equipped with full face mask with filter made a first rescue attempt but had to stop because of the limited protection of the filter masks After a tedious search by search teams under the protection of compressed air equipment, both victims were found dead. Case Study Toxic cloud F.Verschueren MAHB JRC ISPRA 05/11/