City of Sidney, Ohio - Water Treatment Plant - Executive Summary
The City of Sidney Water Treatment Plant (WTP) is committed to minimizing the risk to employees and to the public of injury or death from an accidental release of chlorine. Chlorine gas is the only regulated substance at the WTP and is used for disinfection of the City's water supply. The chlorine gas is dissolved in water (through a chlorinator) to form the disinfection agent, liquid chlorine. The maximum amount of chlorine in this process at any one time is 4000 pounds. This represents two full one-ton cylinders being connected simultaneously. This amount exceeds the threshold for EPA's Risk Management Planning of 2500 pounds. There are possible offsite consequences from a chlorine release, but the facility is not covered by OSHA's process safety management standard. Therefore, the Sidney WTP is only subject to risk management program level 2. |
The Sidney WTP maintains up-to-date, accurate, written operating procedures that provide clear instructions for the chlorine process.
These operating procedures are instrumental in ensuring safe operation of the systems and preventing accidental releases. An equipment failure could also result in an accidental release. The WTP has a maintenance program that is also critical to maintain the on-going mechanical integrity of the process equipment. The Plant Superintendent ensures that all chlorine process safety information is kept up-to-date, and maintained in a format that provides easy access for employees.
The Plant Superintendent ensures that all operators have the required training to properly and safely operate the chlorine process. All new employees must complete at least 8 hours of initial training, which consists of chlorine specific safety and health hazards, process operations, and emergency operations including shutdown. Each employee must also complete at least 4 hours of refresher training every three years. The refresher training covers a review of all topics presented in the initial training, as
well as any changes to the chlorine process or equipment. Written examinations are given to evaluate the employees' proficiency following the training sessions.
Hazard reviews are conducted to identify, evaluate, and control the risk associated with process hazards and chlorine release scenarios. The overall purpose is to prevent or minimize the effects of a release. The hazard review is conducted on the entire chlorine system. The Plant Superintendent updates the hazard review at least once every five years, or when a major change occurs in the process.
A chlorine gas leak to the atmosphere is the primary hazard associated with this process. The worst case scenario would be represented by the complete failure (rupture) of a one-ton cylinder outside of the chlorine room, releasing 2000 pounds of chlorine into the air. Using EPA's guidance criteria, this release is calculated to take place over 10 minutes. At a wind speed of 3.4 mph, the chlorine gas would travel 3.0 miles bef
ore the concentration drops below the toxic endpoint, the level at which chlorine gas is no longer a hazard to the public. Depending upon the wind direction, such a release could affect anyone within the city and surrounding area. The population within a 3.0 mile radius of the WTP was estimated to be 20,000 people. This was determined using the "LandView" computer software developed by the EPA and NOAA (National Oceanic and Atmospheric Administration).
Numerous alternate release scenarios resulting from the failure of valves or broken piping were considered. Different variables were used in evaluating each different situation. These include the size of the opening, pressure and release duration. The "alternate release" scenario chosen represents a more plausible possibility than the loss of a complete cylinder. This situation involves the failure or damage of the gas valve on the chlorine tank, before the vacuum regulator. This would allow chlorine gas to escape uncontrolled f
rom the valve for an estimated time of one hour. This type of release would occur within the chlorine room of the water plant, which would provide a reduction in the release rate to the atmosphere. Using EPA's guidance criteria, the total release would be 477 pounds. At a wind speed of 6.7 mph, the chlorine gas would travel 0.2 miles before the concentration drops below the toxic endpoint. Those affected by such a release would be primarily the residents near the WTP. The population within a 0.2 mile radius of the WTP was estimated to be 100 people. This was determined using the "LandView" computer software developed by the EPA and NOAA (National Oceanic and Atmospheric Administration).
During the past five years, there have been no accidental releases of chlorine from the Sidney WTP in which chlorine escaped offsite. Minor leaks have been noted within the chlorine room and were handled promptly by WTP personnel. These type responses are incidental, and are not considered a re
sponse action. No threat was posed to the public or the environment.
In the event of an accidental release, the WTP emergency action plan contains the procedures for evacuation of the plant and immediate notification of the fire department. The fire department's hazardous materials response unit is responsible for control of the chlorine leak and evacuation of any affected residents. The fire department has a copy of the WTP risk management plan and conducts yearly inspections to review plant operations, equipment and procedures.
Recent improvements have been made to the chlorine system. Chlorine gas was previously moved by pressure to the chlorinators. The chlorine gas is now transferred from the cylinders to the chlorinators completely by vacuum. In the event a line is broken, air is sucked into the piping instead of letting chlorine escape. At the same time a vacuum relief valve located on the cylinder would close to keep pressurized chlorine from escaping from the cylinder
. This greatly reduces the possibility of an uncontrolled chlorine release.