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Explosion during distillation of 3:4 Dichloro aniline

In a chemical factory producing o-chloro para nitro aniline, 3:4 dichloro aniline, 2:3 dichloro aniline, 3:5 dichloro aniline, meta-toludine etc. 3 explosions occurred at intervals of a few seconds and there was a fire.on 4-7-2002 at about 8.30 A.M.’ during distillation of 3:4 Dichloro aniline.

Incident: Charging of 3:4 dichloro aniline crude (about 12 ton) was completed on 3-7-2002 in the second shift. Then vacuum were applied. Heating was there started. Within half an hour. Temperature of the column reached the desired level. In the second shift of 3-7-2002, vacuum, re-boiler and column were working satisfactorily. On 4-7-2002, about 1.5 Ton material collected in the low boiler inter cut receiver whereas 10 Ton material (3:4 DCA) was in process in the re-boiler and column. At about 8.00 A.M. on
4-7-2002 vacuum were found low and mercury in the meno-meter was thrown off. Thus due to vacuum failure, system was pressurized. Vent valve of the vacuum trap was opened. At that time, 3 explosions occurred at intervals of a few seconds and there was a fire.

Cause of the incident: During distillation of 3:4 Dichloro aniline, vacuum failed and heating in the re-boiler was going on there was a rise in the temperature of the distillation column. Because of the rise in the temperature, partial decomposition of 3:4 dichloro aniline took place and hydrogen chloride and tar were produced. 3:4 dichloro aniline reacted vigorously with hydrogen chloride in presence of catalyst. Temperature and pressure of the column could not be controlled resulted in an explosion, followed by fire.

Area & persons affected: 4 workers died, 4 were seriously injured, 3 workers received ...... injuries. Fire brigade personnel were injured during the rescue operation. Entire plant (3:4 DCA) collapsed. Some of the parts of the structure and condenser flew off and fell in the nearby shed about 70 to 80 feet away.

Action to be taken for non repetition of such incident:

¨ Instead of oil heating system in the re-boiler for heating 3:4 DCA, steam heating system shall be provided and it shall be interconnected to vacuum system in such a way that if the vacuum drops beyond safe limits, steam supply shall be cut off immediately.
¨ Appliances provided on the distillation column and healing system shall be examined and tested by competent person and records shall be kept.
¨ Processes carried out in the factory shall be isolated from each other.



 

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