In the Castleford, UK incident, which event occurred first?

• A. Heat applied to residue through an internal steam coil
• B. Residue self-heated
• C. Runaway reaction occurred
• D. Evolved vapors ignited

Answer: (A)

The event that starts the sequence is heating the residue through the internal steam coil. Supplying heat to the residue provides the energy that initiates its decomposition. Organic residues often decompose exothermically, and once heat is applied, the temperature of the residue rises. As the temperature climbs, the rate of the exothermic reaction increases, and heat generation can outpace removal, leading to self-heating. If cooling is insufficient, this accelerates into a runaway reaction, with rapidly rising temperature and pressure. From there, vapors are evolved, and if an ignition source is present, those vapors can ignite. So the initial heater input is the first event that triggers the entire sequence.