Incidents explosion, runaway reaction

A publication summarises all the then available technical evidence related to the Seveso accident, and recommends operational criteria to ensure safety in commercial processes to produce trichlorophenol [4], All the plant scale incidents were characterised [ 1 ] by the subsequent occurrence of chloracne arising from the extremely toxic and dermatitic compound 2,3,7,8-tetrachlorodibenzodioxin (structure IX, p. S-3), formed dining the thermal runaway reaction and dispersed in the ensuing explosion. It is also extremely resistant to normal chemical decontamination procedures, and after the 1968 explosion, further cases occurred after transient contact with plant... 

In a review of incidents involving explosive reactivity of liquid chlorine with various organic auxiliary materials, two involved hydrocarbons. A polypropylene filter element fabricated with zinc oxide filler reacted explosively, rupturing the steel case previously tested to over 300 bar. Zinc chloride derived from the oxide may have initiated the runaway reaction. Hydrocarbon-based diaphragm pump oils or metal-drawing waxes were violently or explosively reactive [8], A violent explosion in a wax chlorination plant may have involved unplanned contact of liquid chlorine with wax or chlorinated wax residues in a steel trap. Corrosion products in the trap may have catalysed the runaway reaction, but hydrogen (also liberated by corrosion in the trap) may also have been involved [9],... 

On April 8, 1998, a runaway reaction during the production of Automate Yellow 96 dye initiated a sequence of events that led to an explosion and fire at the Morton International, Inc., plant in Paterson, New Jersey. On the day of the incident, flammable materials were released as the result of an uncontrolled rapid temperature and pressure rise in a 2,000-gallon kettle in which ortho-nitrochlorobenzene and 2-ethylhexylamine were being reacted. Nine employees were injured in the explosion and fire, including two seriously. Potentially hazardous materials were released into the community, and the physical plant was extensively damaged. 

Information gained from simulations can reveal key insights that explain gaps or contradictions in information. The time line is a useful tool in this development. For incidents of unexpected chemical reactions, it is common to attempt a lab scale simulation of the conditions involved in the exotherm or explosion. Many chemical processes can be modeled and duplicated dynamically by computer algorithms. Accelerated rate calorimeters (ARC) have proven to he highly useful tools for studying exothermic or overpressure runaway reactions. 

The thermal risk linked to a chemical reaction is the risk of loss of control of the reaction and associated consequences (e.g. triggering a runaway reaction). Therefore, it is necessary to understand how a reaction can switch from its normal course to a runaway condition. In order to make this assessment, the theory of thermal explosion (see Chapter 2) needs to be understood, along with the concepts of risk assessment. This implies that an incident scenario was identified and described, with its triggering conditions and the resulting consequences, in order to assess the severity and probability of occurrence. For thermal risks, the worst case will be to lose the cooling of a reactor or in general to consider that the reaction mass or the substance to be assessed is submitted to adiabatic conditions. Hence, we consider a cooling failure scenario. 

The Flixborough nylon plant accident in the UK (1974) was caused by an open-air explosion of a flammable gas released into the air. It killed the 28 plant employees present and caused extensive property damage in the surrounding area. The failure to perform a full technical assessment of a modification was given as the main cause of the event. The Seveso pesticide plant accident in Italy (1976) is well known for the dangerous release of dioxin due to poor plant safety features and to the underestimation of the possibility of a runaway reaction. The Bhopal incident in India (1984), at another pesticide plant, killed an estimated 4000 (although the total number is still unknown). This disaster was attributed to too large an inventory of toxic substances and to very poor staff attention to the operability of safety features. 

Most laboratory reactions are carried out on a small scale, where adequate cooling and agitation can prevent a runaway reaction. Nevertheless, runaway reactions have resulted in significant laboratory incidents. Incident 5.3.10.1 is an example of a runaway reaction that resulted in an explosion with injuries. Incident 5.3.10.2 illustrates how common reactions such as those involving Grignard reagents can result in runaway reactions with adverse results in the laboratory. 

Rayner, P., Safety Digest Univ. Safety Assoc., 1991, 40, 14 A methyl but-3-enylimidate ester hydrochloride, was charged to a tenfold excess of stirred 14% hypochlorite solution cooled in ice. After 50 min the flask was removed to replenish the ice. Shortly after returning the flask to the icebath a violent explosion shattered both flask and icebath. This was attributed to thermal runaway (although available energy is scarcely sufficient to boil the water in the flask). It seems more likely that trichloroamine was generated by the excess hypochlorite, settled when removed from the magnetic stirrer, and detonated from friction when this restarted. The reaction is said to have been performed many times previously without incident. 

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