a medium size factory manufacturing ethyl cellulose
explosion followed by fire took place on16-3-2002
around 19.30 hours
Company was manufacturing ethyl cellulose using caustic
flakes, wood pulp, ethyl chloride, air, recovered
solvent (crude eather) at 120ºC temp. And 22
to 23 kg./cm2 pressure. This reaction is an exothermic
reaction. Once the above-mentioned temperature is
achieved, steam supply is stopped. Temp. 145ºC
and 28-30kg/cm2 is pressure is maintained for 16-20
hrs. Thereby ethyl cellulose is produced.
Company had changed the process. Instead of air, pure
oxygen from cylinder and cobalt chloride was used
as a catalyst so as to reduce the time cycle. In addition
to this, the reactor, parallel reflux line were fabricated
in-house and installed to recover the solvent vapour
generated during reflux.
With the above changes in the process and modifications,
the process was started. Pressure inside the reactor
was suddenly raised. Reflux line from the welding
broke. Flange of the bottom valve provided at the
reactor bottom also broke and ball inside ball valve
was thrown out due to pressure and there was an explosion
followed by fire.
Cause of the incident:
Ethyl Chloride is a highly explosive material. It
reacts vigorously with oxidizing agent. Pure oxygen
from the cylinder and cobalt chloride was used as
a catalyst. Because of this, vigorous reaction started
and pressure inside the reactor rose suddenly. Stop
valve which was installed before the safety valve,
was closed, and so the safety valve and rupture disc,
which were installed on the reactor, could not function.
Valve on the reflux line was opened and due to this,
pressure was exerted in the reflux line and it broke
from the welding. Flange of the bottom valve broke
and ball inside the ball valve was thrown out with
pressure. Material inside the reactor came out with
pressure and there was an explosion followed by fire.
Area & persons affected: Due to this accident
2 workers died on the spot and 4 workers died during
treatment. Plant, building and equipment was also
Action taken for non-repetition of such incident:
¨ Safety valve of adequate size shall be mounted
on the pressure vessel (ethoxylation reactor). The
outlet of the safety valve shall be connected to blow
down tank. Vent shall be provided on blow down tank
and outlet of the vent shall be connected with flame-arrestor.
¨ Reaction vessel shall be isolated with other
process by fire retardant material and explosion
¨ Before making any change in the process, process
details, its hazards and measure to control the same
shall be communicated to CIF before 15 days.
¨ Non-sparking tools shall be used wherever flammable
and explosive materials are used in the factory.
¨ Any addition on the pressure vessel/repairing
is carried out, it shall be tested by competent person
before it is put to use and the testing report in
the prescribed form shall be kept.
¨ Sensor with alarm shall be provided for detection
of ethyl chloride and other solvent.
¨ Considering the complete safety of the worker,
trial/laboratory/pilot experiment shall be carried
out before making any change in the process