Explosion in a Waste Tank of a Pharmaceutical Plant
An explosion occurred around noon while conducting hot work (with a disc saw) on a 320-m fixed-roof tank at a pharmaceutical plant employing 240 personnel. The tank belongs to a waste treatment unit as part of an antibiotic production process. The tank cover was blasted 20 m away and the subcontractor performing cutting works was killed. Three other subcontractors and a plant employee were severely burnt and injured by the shock wave. Notified by neighbours and not by the operator, fire fighters arrived on the scene 15 min after the explosion and promptly extinguished the fire. Municipal and provincial authorities as well as Regional Environmental Agency officials were duly informed of the accident; the operator issued two press releases.
Event Date
June 10, 2010
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
IMMEDIATE CAUSE:Anaerobic fermentation of both the liquid phase and a solid deposit in the thank was responsible for generating explosive gases (especially hydrogen and methane). Sparks generated while the subcontractor was working adjacent to the air duct triggered the ignition and the explosion of the flammable mixture. The duct had been temporarily disconnected but not sealed. ROOT CAUSE:Under normal operations, the tank collected a liquid fermentation residue composed of water and micro-organisms assumed dead. The initial design included an air injection circuit at the tank bottom and a suction circuit at the level of its vent, in order to homogenize effluent. That system was shut down (10 years prior to the accident) it was considered redundant as a mixing baffle had already been installed at the tank bottom but this resulted in the formation of an anaerobic atmosphereSeveral deficiencies were observed regarding works organization, namely: lack of precision in written procedures governing hot works and poor understanding of procedures among employees and subcontractors, plus inadequate subcontractor expertise (as demonstrated by failure to plug the duct).
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
waste treatment tank, antibiotic production
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
The TKX, located in the waste treatment unit of the principle O production process, was used to homogenize the BES for its storage. The BES, with high organic amount and a COD (chemical oxygen demand) of 80 g/l, was sent to the TKX from the stripping unit at a flow-rate of about 2-3 m/h. The maximum design-filling of the TKX was 50% of its capacity.During its 2 to 3-day stay inside the TKX, the BES was shaken by the internal helical lateral mixer and mixed with a caustic soda solution at 30% in order to maintain a fixed pH (around 8-8.5). After homogenization and equalization in the TKX, the BES was transferred to a bioreactor (TKY) for the stabilization treatment: a biological pre-treatment to reduce COD by almost 70% before sending the BES to a lagoon. In its original design, the TKX was equipped with an internal system to insert and spread the air and an external systemto suck air out. These systems, not operative at the moment of the accident, should have been active during normal TKXoperation (Figure 3), planned as follows:1. introduction of air into the internal liquid mass (BES) through the sparger system at the bottom of the tank;2. extraction of air and gas formed through a sucking system, located on the roof and connected to the vent.In March 2000, during revamping of the TKX, the air system was considered as additional with respect to the internalhelical lateral mixer, and responsible for causing bad smell and foam. As a consequence, it was locked off.
Lessons Learned
Lessons Learned
The analysis puts in evidence several Seveso II Directive faults in the following three aspects: IDENTIFICATION OF POSSIBLE ACCIDENTAL EVENTS, SAFETY ANALYSIS AND RESIDUAL RISK:The risk assessment did not identify all ATEX areas inside the establishment, as expected from the operator. The classification, size and location of a particular zone depend on the probability of an explosive atmosphere to appear and its persistence if so. The classification needs to take into account not only the present hazardous substances, but also the possible unwanted formation of other dangerous substances. PERSONNEL TRAINING: The work permit procedure was not adequately applied during the maintenance operation and work permits forms were not correctly filled by both contractor and operator. In particular, the safety measures required for hot maintenance operations, such as the closing of openings, were not adopted. OPERATIONAL CONTROL AND MAINTENANCE PROCEDURES: the written procedure was unclear and not easily understandable by the staff, particularly as concerns the delivery of authorization to the contractor by the Direction/SMS responsible, as noted above.
Event Nature
Emergency Action
The internal emergency plan was immediately activated; the internal team provided first aid for the four injured operators, and transferred them to the nearest hospital. The plant was shut down and put in safe condition.External fire brigades arrived 15 minutes after the accident, found the dead worker on the roof of the TKY and checked the safety of the area using an ATEX detector. The fire brigades were not called by the operator, but by people from outside the plant who heard the explosion. The emergency situation was cleared within 4 hours. Local authorities arrived together with the judicial authority, which closed and sealed the whole area.
Emergency Evaluation
A detailed investigation was carried out by the judicial authority, supported by the Regional Environmental Agency and technical experts. In July 2012, 15 persons were charged (among which the supervisor and the safety responsible of the plant).
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
full report from ARIA data base
event no. 38557
Brief description ARIA data base
event no. 38557