City of Phoenix - South Division Transit Facility - Executive Summary |
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The City of Phoenix South Transit Division developed this document to meet the requirements for a Program 2, Risk Management Plan (RMP) under the Accidental Release Prevention Program, Clean Air Act Amendments of 1990 for its liquefied natural gas (LNG) and compressed natural gas (CNG) fueling system located at 2225 West Lower Buckeye Road, Phoenix, Arizona. This RMP was prepared in accordance with the following Federal requirements: 7 US Environmental Protection Agency (USEPA) requirements in 40 Code of Federal Regulations (CFR) Part 68 The City of Phoenix prepared this RMP in conjunction with the Arizona branch of EMCON Environmental Associates (EMCON). Data elements for this RMP are electronically submitted to the USEPA. Technical documentation for the off-site consequence analyses, the Process Hazard Review, Prevention Program, and Emergency Response Procedures are retained on file at The City of Phoenixs Public Transit South Division facility. The equipment and facilities at the South Division operation are owned by the City of Phoenix. ATC/Vancom, which is under a management contract to the Public Transit Department provides personnel and training to operate the LNG/CNG system. The Phoenix Transit System (PTS) will implement this Risk Management Plan. The City of Phoenix Accidental Release Prevention & Emergency Response Policies The City of Phoenixs policy is to conduct all operations in a safe and conscientious manner to prevent accidental releases of any hazardous material, including substances regulated through the Federal Accidental Release Prevention Program. The City of Phoenix trains its employees at this facility to properly handle and store hazardous materials to minimize the possibility of adversely affecting its worker's health, the workplace, the public, and the environment. A combustible gas and flame detection system, using ultraviolet/infrared technology, operates continuously at the storage, fueling, and maintenance areas containi ng liquefied natural gas (LNG) and compressed natural gas (CNG). The City of Phoenixs Accidental Release Prevention policy is implemented through the PTS management system at the South Division. The City of Phoenixs emergency response policy is contained in its current written Hazardous Materials Management Plan. PTS provides 24-hour security service for the facility. In the event of an emergency, PTS will contact the Phoenix Fire Department to respond. A designated Emergency Coordinator (EC) initiates emergency notifications and evacuations. All PTS employees are trained in their appropriate role in emergency response and proper procedures for awareness level response. The South Division facility maintains a highly cooperative relationship with the Phoenix Fire Department to ensure a full understanding of LNG/CNG system and emergency response and evacuation procedures related to regulated substances. General Description of Regulated Substance and Stationary Source The Cit y of Phoenix's South Division facility is located at 2225 West Lower Buckeye Road in an industrial area. The site covers approximately 15.4 acres and is used for fueling, maintenance, and parking of Transit Division buses. Operations for the LNG/CNG system include delivery of LNG to the storage system, conditioning of the LNG, generation and storage of CNG, dispensing of LNG to City buses, and dispensing of CNG to City passenger cars. The North American Industrial Classification System (NAICS) code for this process is 48511, Urban Transit Systems. LNG is a colorless, odorless liquid consisting primarily of methane and lesser amounts of ethane and carbon dioxide. LNG is a federally regulated flammable substance subject to Risk Management Plan requirements if there are more than 10,000 pounds present in a process. The LNG inventory at South Division is contained primarily in the two storage tanks. These tanks are situated on a concrete pad and surrounded by a concrete containment structure designed to hold the entire capacity of the two tanks. The LNG is conveyed to the three fuel dispensers on the nearby fueling islands in double-wall vacuum-jacketed piping. Specially designed fill hoses with a sealing quick-disconnect nozzle are used to fill the LNG storage tanks on the buses. All the LNG storage and fueling operations are conducted in areas with combustible gas and flame detectors that completely shut down the system should a combustible gas release or fire be detected. Off-Site Consequence Analyses Results The RMP Program requires the evaluation of an accidental release of the regulated substance, in this case LNG, from the process being considered. In its General Guidance for Risk Management Programs, July 1998, USEPA states that it should be kept in mind that the results obtained from modeling release scenarios should not be considered to predict the likely results of an accidental release. The assumptions made in the computer models are very c onservative and tend to overpredict the impact from an accidental release. The results from such models have a high degree of uncertainty and should be viewed as providing a basis for discussion, rather than hard predictions. As required by USEPA for the RMP, the City of Phoenix assessed two types of release scenarios for the LNG/CNG system. The first scenario is a worst-case release which is mandated by USEPA to be the release of the largest quantity of a regulated substance that results in the greatest distance from the point of release to a specified endpoint (40CFR'68.3). The second scenario is an alternative release scenario which is more likely to occur than the worst-case scenario and reaches an endpoint offsite. Details of these two scenarios are presented below. Worst-Case Release Scenario USEPA requires that the worst-case release scenario be the release of the entire contents of the single largest vessel containing the regulated substance. For flammable substance s, USEPA requires that we assume all the flammable material is released into a vapor cloud which is then ignited and results in a vapor cloud explosion. For flammable substances, the specified endpoint is an overpressure level of 1 pound per square inch (psi) from the explosion of the vapor cloud. The endpoint of 1 psi is intended to be conservative and protective; it does not define a level at which severe injuries or death would be commonly expected. An overpressure level of 1 psi is unlikely to have serious direct effect on people but may cause property damage such as partial demolition of houses. It should be noted that USEPAs Guidance document states that vapor cloud explosions are unlikely events. USEPAs RMP*CompT model was used as the method for estimating the distance to the endpoint of 1 psi. The RMP*CompT default values for release duration, wind speed, and atmospheric stability class were utilized for this modeling. These default values are very conservative in pr edicting the distance to the endpoint. The worst-case release scenario was designated as the release of 95,000 pounds of LNG from one of the storage tanks within the containment area and the subsequent vapor cloud explosion of this chemical. There is no passive mitigation available for this scenario and no other containers are affected by this release. The distance from the site of the release to the endpoint extended beyond the boundary of South Division. Public receptors are located within this distance to the endpoint. Alternative Release Scenarios The alternative release scenario gives us an opportunity to present a potential release impact which is more credible than the worst-case scenario. We have evaluated two possible alternative release scenarios below. However, it should be noted that given the safety and accident prevention mechanisms in place at South Division, these alternative release scenarios are not considered to be highly likely. The RMP*CompT default va lues for release duration, wind speed, and atmospheric stability class were utilized for this modeling. Once again, these values are very conservative. 7 Scenario 1: A bus drives away from the fueling island before disconnecting the fill hose from the LNG dispenser. This scenario is highly unlikely since an interlock is present which prevents the bus from being started with the fuel door open. The fill hose is assumed to rupture allowing LNG to flow out of the dispenser until the excess flow valve and the combustible gas detectors shut down the dispenser pump and entire LNG system electrics. We have conservatively assumed that 250 gallons of LNG is released from the ruptured hose. We have also assumed that the vaporizing LNG reaches an ignition source and forms a vapor cloud fire instead of a vapor cloud explosion as in the worst-case release scenario. No other containers are affected by this release. The distance from the site of the release to the endpoint extended beyond the boundary of South Division. Public receptors are located within this distance to the endpoint. 7 Scenario 2: A transfer hose fails while off-loading LNG from the transport truck to the LNG storage tanks. The transfer hose is assumed to rupture allowing LNG to flow out of the transport until the excess flow valve shuts down the transport line. A check valve prevents LNG in the storage tank being loaded from flowing back out of the process line. The excess flow valve would close almost immediately, however we have conservatively assumed that 1,100 gallons of LNG is released. We have also assumed that the vaporizing LNG reaches an ignition source and forms a vapor cloud fire instead of a vapor cloud explosion as in the worst-case release scenario. No other containers are affected by this release. The distance from the site of the release to the endpoint extended beyond the boundary of South Division. Public receptors are located within this distance to the endpoint. Summar y of the General Accidental Release Prevention Program & Chemical Specific Prevention Steps The City of Phoenix's release prevention program complies with Federal Accidental Release Prevention requirements for LNG. The City of Phoenix's prevention program emphasizes thorough training for its employees in hazard communication; proper handling, transfer, and storage methods; and awareness level emergency response. The City of Phoenix's standard operating procedures include diligent observation of the LNG/CNG system vessels, piping, valves, and other equipment during off-loading, conditioning, and dispensing of LNG. The entire LNG/CNG system is designed and constructed in accordance with the Uniform Fire Code, the Uniform Building Code, National Fire Protection Association (NFPA) articles, American Society of Mechanical Engineers (ASME) standards, and other agencies having jurisdiction. No smoking is allowed within 50 feet of any equipment containing LNG or CNG. All system component s are grounded to prevent sparking, including the transport vehicle during off-loading. A combustible gas detection system and a flame detection system monitor the LNG containment area and the fueling islands continuously. All valves within the LNG/CNG system are air actuated and are tied to the combustible gas and flame detection systems. If combustible gas or flame is detected by the sensors, the entire LNG and electrical system is shut down so that no LNG can be moved into or out of the system. In the event of release or flame detection, audible and visual alarms will sound to initiate emergency response procedures. Summary of 5-Year Accident History On the basis of a review with the City of Phoenix during preparation of this RMP, there have been no accidents or accidental releases involving the South Division LNG system since it was brought on-line in July 1998. Summary of the Emergency Response Program The City of Phoenix's South Division facility has a written Hazardo us Materials Management Plan which contains the Emergency Response Procedures. The focus of the plan is to protect the public, protect employees, protect public property, and protect Transit System facilities. The plan designates a list of Emergency Contacts (EC) for implementing the procedures. The key role of the EC is to initiate notification and evacuation procedures in the event of a release or fire. Other employees receive awareness level emergency response training and hazard communication training. The facility uses a continuous combustible gas detection system and a continuous flame detection system to monitor for releases 24 hours a day. Immediately after discovering a release of combustible gas, South Division personnel are instructed to notify the Phoenix Fire Department for initial response and evacuate the area affected by the release. If it is safe to do so, personnel may stop the source of a leak to reduce the potential impact of a release. Emergency Shutdown (ES D) buttons are also available to be manually activated to cease operation of the LNG/CNG and electrical system. Planned Changes to Improve Safety The City of Phoenix South Division Transit facility has an excellent safety record and is continually evaluating ways to improve safety at the site. LNG system operators and maintenance personnel are continuously trained and updated in the hazards of LNG and proper operation and maintenance of the LNG/CNG system. Additionally, a strong Operations & Maintenance checklist and comprehensive Preventive Maintenance procedures assure the system components are in safe working condition. |