Yantai, Shandong – Wanhua has been fined and employees have been penalised as a result of an investigation report on the explosion at its Yantai site on 20 September 2016.
The explosion in an intermediate bulk storage tank for crude MDI caused four deaths and four injuries, resulting directly in CNY5.7m ($840,000) financial loss.
The investigation, carried out by local authorities and chemical industry experts, concluded that a manually-controlled ball valve retainer had been damaged and was not shut down properly during maintenance and that the control panel operator did not turn off the piping valve remotely according to standard operational procedure.
These failures caused a leak into the system which reacted with crude MDI and generated urea and biuret reactions. Products from these reactions then entered the MDI storage tank and became a catalyst for crude MDI’s self-polymerization at high temperature (200℃), generating carbon dioxide.
High-viscosity polymers and urea chemicals formed by the self-polymerization clogged the pipes leading to and from the tank, and the rising pressure caused by increasing carbon dioxide resulted in the explosion.
The report said that there were a number of management failures which lead to the explosion.
It said that:
- The control panel operator had not been warned that the valve had not been closed properly;
- No one noticed the anomaly in the tank, realised its potential risk or warned anyone else and that;
- Operators and supervisors were not aware of the catalytic effect of urea chemicals in MDI condensation reactions prior to the accident and did not foresee such grave outcome.
Relevant employees have been penalized and the company was fined CNY 800,000 the report said. Wanhua has been ordered to tighten up procedures.