Chlorine leak incident

Thanks to Mr Harbhajan Singh Seghal for sending this incident report:

INCIDENT OF CHLORINE LEAKAGE
Two persons were gassed in one of the chlorine consuming industry near Baroda. When the operator disconnected the tonner on the pretext of the hard valve operation of the tonner.
DETAILS OF INCIDENT 

The consumer withdraws liquid chlorine and consumes gas after evaporation.
As per practice the consumer keeps the tonner in line to withdraw maximum chlorine from the tonner.
On the specific date the operator tried to isolate the tonner at 1.0kg/cm2 pressure when about 40-50 kgs liquid chlorine was there in the tonner and ice formation was there at the bottom of the tonner.
He could not close the valve fully. The spindle of the valve damaged due to excessive force.
The operator decided to cut off the tonner by wearing SCBA.
This action resulted in heavy gas and affected two persons in the surrounding 

ROOT CAUSE OF THE PROBLEM

• Liquid chlorine withdrawal rate is 180 kgs/hr. Maximum liquid chlorine is used up in 4-5 hrs operation at this rate. Some quantity 40-50 kgs remains in the tonner at the bottom. Some consumers try to recover this as gas by keeping the tonner in line for more time This Liquid chlorine evaporates at 5-6 kgs/hr as gas and lowers the temperature of the tonner/pipe lines due to fall in pressure till the exhaust of liquid chlorine. 1.0 kg/cm2 pressure can lead to about -20 degree C and takes 8-10 hrs to become completely empty.
• Normally chlorine in the tonner is dry. But under such conditions (-20 degree) the same chlorine become wet. Water in the chlorine separates out and freezes in the sprindle of the chlorine valve. It makes the valve hard to operate at that time.
• After achievement of normal temperature chlorine evaporates first and water later. This chlorinated water reacts with the spindle and makes the chlorine spindle greenish.
• The evaporators which do not have backflow prevention system (from evaporator to chlorine tonner) results carry over of iron chloride rust to valve spindle and makes the valve hard in operation.

ACTION TAKEN

• The tonner brought to the works.
• It was depressurized and valve dismantled.
• Iron chloride rust and greenish color sludge observed in the threading of the valve.
• Damaged valve replaced with new valve.

SUGGESTED ACTION

• The tonners containing some quantity of liquid chlorine are not to be cut off at 1.0kg/cm2 till Chlorine pressure is released to neutralization system through header or evaporator.
• No Cl2 gas from the upper valve of the tonner
• No ice formation appears on tonner or pipe lines after depressurization.
• Chlorine header and evaporator must have chlorine release facility connected to neutralization system.
• Chlorine evaporator must have liquid chlorine flow control interlocked with temperature and outlet pressure to avoid the back flow of chlorine.
• Evaporator should have emergency release system with rupture disc and safety valve.
• Temperature of evaporator should be maintained between 80-85 degree C to avoid formation of rust as FeCl3 in the evaporator.
• Dry air (-40 degree) dew point is to be utilized for evaporation maintenance.
• Glass wool filter is to be utilized in gas line to avoid carry over of Fecl3 to main products and choking in chlorine system.
• Tonners can be kept in tilted position forming 20-30 degree angle to withdraw maximum liquid chlorine from the tonner.

CONCLUSION

• No chance should be taken with liquid chlorine system. Help of the filler must be taken in such cases. One volume of liquid chlorine expands to 460 times
• Chlorine neutralization system must be effective and checked from time to time.
• Single person should not take this type of emergency job.
• Always there should be two persons with safety equipment.