DART - Northwest Bus Services Facility - Executive Summary |
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ACCIDENTAL RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES It is the Dallas Area Rapid Transit's (DART's) policy to adhere to all applicable federal and state rules and regulations. DART is committed to protect the health and safety of its employees and public. In order to achieve this objective, DART has allocated and invested considerable resources in implementing reasonable controls to prevent predictable releases of Liquified Natural Gas (LNG) by training its employees, by the safe design, installation, maintenance and operation of this facility, and by installing ire and leak detection and mitigation systems. FACILITY DESCRIPTION AND THE REGULATED SUBSTANCES HANDLED DART owns and operates the Northwest Bus Services Facility (Northwest Facility) in Dallas, Texas. The primary purpose of this facility is to fuel the LNG bus fleet. LNG is delivered by truck and is stored in two 30,000-gallon horizontal cylindrical storage tanks. Access to the site is restricted to authoriz ed facility employees, management personnel, and contractors. The regulated substance handled at this fueling facility is LNG. Methane, which is the major component in LNG, is considered hazardous by the United States Environmental Protection Agency (EPA). LNG is a flammable liquified gas. It is stored at -258.7 0C. It is a clean burning fuel. The maximum intended inventory of LNG at this site is 60,000 gallons (212,400 lb). The properties that make LNG a valuable fuel also necessitate the observance of certain precautions in handling LNG to prevent unnecessary human exposure, to reduce the threat to the health of DART personnel, and members of the nearby community. WORST-CASE RELEASE AND ALTERNATIVE RELEASE SCENARIOS Worst-Case Release Scenario According to EPA requirements, the worst-case accident scenario at the Northwest Facility is the catastrophic rupture of the two LNG storage tanks, the complete vaporization of their contents, and the explosion of this vapor cloud. The two tanks are in close proximity such that the failure of one tank may lead to the failure of the other. Each LNG tanks holds 30,000 gallons of LNG. The total amount of LNG released is 212,400 lb. The Multi-Energy Model was used to identify the hazard zones that were then used to predict the flammable endpoint. The worst-case release of LNG is predicted to have offsite impacts on public receptors. Alternative Release Scenario Since the worst-case release scenario predicted offsite impacts, an alternative release scenario involving LNG is reported. The alternative release scenario is defined as a flash fire due to the rupture of the 3-inch transfer house or the sudden hose uncoupling. The spill occurs in the unloading area and is not confined. The amount of LNG released is 5310 lb. LNG vapor evaporating from the unconfined pool travels to the lower flammability limit (LFL) and will cause a flash fire if ignited. The distance to the LFL for this alternative release scena rio was found using the DEnse GAS DISpersion (DEGADIS) model. No offsite impacts are predicted to occur from the alternate release of LNG. GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAM AND CHEMICAL-SPECIFIC PREVENTION STEPS DART will continue to protect the environment and the health and well-being of fellow employees and communities by ensuring that LNG is safely handled and stored on-site. DART has taken several measures to eliminate the occurrence of a LNG spill or release, including training of DART employees, the safe design, installation, maintenance, and operation of the facility, and by installing fire and leak detection and mitigation systems. DART provides ample training for the existing and new employees. Regular training ensures that each employee demonstrates competence in the operating and emergency procedures. DART has an on-going maintenance program to uphold the mechanical integrity of the process equipment that contains LNG. DART has established procedures fo r investigating an accidental release of LNG. FIVE-YEAR ACCIDENT HISTORY There have been no accidents at the Northwest Bus Services Facility in the past five years that resulted in any adverse onsite or offsite impacts. EMERGENCY RESPONSE PROGRAM The Northwest Facility coordinates its emergency response program with the local fire department. When a leak or fire is observed, facility personnel dial 911, activate the plant-wide notification system, and evacuate the facility if necessary. The local fire department responds to the incident. DART has established written emergency response procedures for spills and fires. PLANNED CHANGES FOR SAFETY IMPROVEMENTS This facility will undergo regular scheduled maintenance and update to meet any new or revised applicable regulation and industry standard to continue to operate safely. |