Summerville CPW Wastewater Treatment Plant - Executive Summary

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The Summerville Commissioners of Public Work's (CPW) accidental release prevention and emergency response policies show that Summerville CPW is strongly committed to employee, public and environmental safety and adheres to all applicable regulations.  The comprehensive accidental release prevention program covers areas such as safety, hazard analysis, operating procedures, maintenance and employee training  associated with the processes at the facility.  The effective emergency response plan covers response procedures such as pre-emergency employee training, lines of authority, emergency recognition, evacuation routes and procedures and emergency medical treatment.  It is Summerville CPW's policy to implement appropriate measures to prevent possible releases of regulated substances. 
The Summerville CPW Waste 
water Treatment Plant has one (1) regulated substance at the facility above the threshold quantity.  The regulated substance is chlorine with a threshold quantity of 2,500 pounds.  Chlorine is used in the wastewater treatment process.  Chlorine is handled in one ton cylinders and the maximum amount of chlorine handled is 18,000 pounds.  Summerville CPW is mandated to meet Program 3 requirements. 
The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case release" and "alternative scenario".  The worst case release scenario is defined by EPA as a release of the largest storage vessel over a ten (10) minute period due to an unspecified failure.  The alternative release is defined by EPA as a release that is more likely to occur than the worst case release.  Summerville CPW chose DEGADIS+ to perform the air dispersion consequence modeling due to the nature of the chemical and the release scenarios. 
The worst cas 
e release scenario submitted for Summerville CPW involves a catastrophic release from a one ton cylinder (2,000 lb.) of chlorine in a gaseous form over 10 minutes.  The chlorine is stored in an enclosed building; therefore, passive mitigation was taken into account.  The mitigated release rate was calculated to be 110 lb/min.  At Class F atmospheric stability, 1.5 m/s wind speed, 104 F, 75% humidity and 0.1 m surface roughness, the maximum distance to the toxic endpoint of 0.0087 mg/L (3 ppm) was determined to be 1.28 miles.  The worst case release did result in offsite impact. 
The alternative release scenario for chlorine involves a fusible plug failure in a one ton cylinder (2,000 lb.) of chlorine.  The fusible plug failure released the entire contents of chlorine in a gaseous form. The chlorine is stored in an enclosed building with a chlorine scrubber; therefore, passive and active mitigation were taken into account.  The mitigated release rate was calculated to be 0.003 lb/min.   
At Class D atmospheric stability, 3.0 m/s wind speed, 63.8 F, 75% humidity and 0.1 m surface roughness, the maximum distance to the toxic endpoint of 0.0087 mg/L (3 ppm) was determined to be 0.025 miles.  The alternative release did not result in any offsite impact. 
The alternative release is much more likely to occur at the facility than the worst case release scenario. The worst case release is unrealistic because when chlorine is released at such a high rate, the chlorine will most likely freeze over the opening in the cylinder which would prohibit more gas from escaping the cylinder.  Also, it is not appropriate to compare a 10 minute release to a one hour standard.  The toxic endpoint concentration is based on a one hour exposure time, while the worst case release occurs over a ten minute period.  Therefore, the ten minute release period is used as the averaging time instead of one hour exposure time.  Realistically, if a person can withstand a certain concentration over a one ho 
ur period with no health effects, they could withstand a higher concentration over a ten minute period.  One solution would be to adjust the toxic endpoint value to correlate to the ten minute exposure during a worst case release instead of the one hour standard.  However, there is no allowance in the RMP rule by the EPA to make this adjustment.  Also, it is not appropriate to assume that the emergency chlorine scrubber will not be operational during a release.  Therefore, due to the capability of the emergency chlorine scrubber, there would most likely be no offsite impact in the event of an accidental chlorine release at the Summerville CPW Wastewater Treatment Plant.     
Summerville CPW has taken all the necessary steps to comply with the accidental release prevention requirements set out under 40 CFR part 68 of the EPA.  The process is subject to the OSHA PSM standard under 29 CFR 1910.119 and is already in complianc 
e.  The following steps are key to the prevention program: 
1. Detailed records of safety information describing the chemical hazards of chlorine, process technology, and process equipment. 
2. Comprehensive process hazard analysis are conducted to ensure that hazards are recognized and evaluated. 
3. Operating procedures have been developed and implemented which describe tasks to be preformed, dates to be recorded, operating conditions to be maintained, emergency operating procedures and safety and health precautions to be taken. 
4. Employee training program is in effect to ensure that the employees of the Summerville CPW Wastewater Treatment Plant are properly trained and aware of all safety practices, hazards, emergency procedures and maintenance procedures. 
5. An on-going mechanical integrity program is in place to ensure safe process operation. 
6. Incident investigation procedures are in place to ensure that all unplanned events affecting process safety are properly investigated in a 
timely manner to identify the causes of the incident and to implement corrective action. 
The Summerville CPW Wastewater Treatment Plant has had an excellent record of preventing accidental releases over the last five years.  Due to the effective release prevention policies, there has not been an accidental release during the last five years. 
Summerville CPW Wastewater Treatment Plant has a written emergency response plan to deal with accidental releases of chlorine and other hazardous materials, which has been coordinated with the local emergency response personnel.  The plan includes all aspects of emergency response including adequate first aid and medical treatment, evacuations, and notification of local emergency response agencies and the public. 
The last Process Safety Hazard Analysis was performed in December 1998 and it resulted in one recommended change at that time.  The change was to c 
ertify the operating procedures which was completed by February 1999.
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