18 October 2004 21:22 [Source: ICIS news]
The blast in a 145-foot distillation tower injured three workers and hurled debris a mile away, igniting several fires on the plant grounds and along a nearby highway.
In an investigation digest distributed today, the US Chemical Safety & Hazard Investigation Board (CSB) said the plant site “lacked an effective system for evaluating hazards and for sharing safety information between different facility operations.”
CSB said the tower that exploded was used to distil mononitrotoluene (MNT), a raw material used to produce dyes, rubber and agrochemicals. The safety board noted that MNT is chemically related to trinitrotoluene (TNT) and can become explosive at high temperatures.
According to the CSB accident investigation, early on the morning of 13 October 2002 plant workers heard a loud rumbling noise and saw smoke venting under pressure from the MNT tower. Just before the tower blew, the three workers took shelter in a control room 50 feet from the tower. The explosion knocked them to the floor and blasted them with glass shards, the CSB said.
CSB said the explosive situation at the First site actually began “weeks before the explosion” when the company temporarily shut down the MNT distillation process, leaving about 1200 gal of MNT in the tower, and then shut off steam system valves to the tower. But what CSB called “aging steam valves” developed leaks and allowed steam to reach the left-over MNT.
“During the days leading up to the explosion,” said CSB, “the hot MNT began to decompose, forming unstable chemicals. Plant operators did not monitor the tower’s internal temperature, which CSB investigators later found had hovered above 400 degrees Fahrenheit.” MNT begins to decompose at temperatures above 370 degrees, CSB noted.
“On 12 October,” CSB added, “a liquid-level alarm activated high on the tower, but no action was taken.” The tower exploded the following morning.
CSB said the company’s instructions to its employees did not provide effective guidance on how to shut off the steam supply to the MNT distillation tower, and the company should have regularly inspected and repaired the steam valves feeding the tower.
The MNT tower also lacked high-temperature alarms and interlocks that could have warned operators and automatically shut down the heat source, the CSB noted.
CSB recommended that the First facility, now owned by DuPont, establish a program for analyzing the hazards of reactive chemical processes, install appropriate safety and warning systems, revise operating procedures and improve preventive maintenance programs.
The Washington, DC-based CSB was established by Congress to investigate chemical accidents and to relate the lessons learned from its investigations to the industry. By law, CSB findings may not be used in litigation.
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