Another Chlorine leakage incident

Thanks to Mr Harbhajan Singh Seghal for sending this incident:
On 18.8.2010 a message was received from Emergency Control Room regarding chlorine leakage in one of the consumers near Vadodara. Immediately the emergency team was sent to attend the problem.
PROCESS / ACTIVITY : The consumer was filling liquid chlorine from 900 kgs to 100 kgs. Cylinders by keeping on weigh balance. The tonner (900 Kgs.cap.) was pressurized with Nitrogen from upper valve. Lower valve of the tonner was connected with the withdrawal pipe fitted with filling valve to 100 kgs. Chlorine cylinder. There was a provision to release withdrawal pipe gas in 200 ltrs. drum containing caustic 100 kgs.
CAUSE OF INCIDENT: During transferring process from 900 kgs. to 100 kgs. liquid chlorine in 900 kgs. tonner exhausted. Pressure of the tonner suddenly gone up due to nitrogen padding. This resulted in very heavy vibration in the withdrawal pipe. Due to this, connection at the both ends was disturbed and damaged the corroded fittings and filling valve due to physical impact. This resulted in heavy gas release from the tonner and cylinder side.
ACTION TAKEN :

• Both the valves of 900 kgs. tonner and 100 kgs. Cylinder were closed after wearing the SCBA (Self Contained Breathing Apparatus).
• Fire hydrant team sprayed water externally to restrict gas in the outer area.
• Police Deptt. controlled the external public for further exposure.
• 10 persons affected with gas during the process were admitted in the hospital which were discharged after first aid.
• Spilled chlorine hydrate was neutralized with Caustic Soda gradually.
• All the tonners were brought back to the plant as per the advise of Explosive Deptt. and depressurized.

All the tonners condition and valves were checked and found perfectly in working order. TECHNICAL / LEGAL LAPSES :

1. Filling of liquid chlorine from 900 kgs. to 100 kgs. was not authorized from Deptt. of Explosives.
2. 900 kgs. Tonner was pressurized manually with Nitrogen pressure from cylinder (max. pressure 150 kg/cm2).
3. Max. pressure required to transfer liquid chlorine to toner is about 10 – 11 kg/cm2 where as uncontrolled pressure was applied manually. It disturbed the transfer process due to high pressure in tonner.
4. There was no well set chlorine neutralizing system. Neutralization was done in 200 ltr. Drum containing caustic.
5. Brazing of copper tube and chlorine valve used for filling was badly corroded and brazing workman ship was very poor. The fitting was not tested at desired pressure.
6. No safety equipments were maintained by the consumer to control any emergency.

LESSONS LEARNT :

1. Filling of liquid chlorine into the tonners can be done after getting the necessary approval from the Deptt. of Explosives.
2. A well set system has to be provided for filling and neutralizing from safety point of view. It is a very unsafe process to transfer liquid chlorine without proper facilities and competent persons
3. Corroded fittings are not be used. Withdrawal pipes needs to be tested and replaced regularly.
4. Provision of pressure regulator and pressure gauge in the line / header is a must.
5. All the safety equipments and gas mask should be readily available.
6. Provision of vacuum system connected with chlorine neutralization system can help to control chlorine hydrate gas due to liquid chlorine spillage.