Texas Ultra Pure, Inc. - Executive Summary
Executive Summary |
Site Description & Regulated Substances
The TXUP Mansfield facility is located within Tarrant County Texas and lies along the southern edge of the Dallas/Fort Worth Metroplex, about 30 miles south of Dallas/Fort Worth International Airport This facility produces high purity electronic grade chemicals that are used in the semi-conductor industry. TXUP was founded in 1997, and the Mansfield facility began production in the third quarter of 1998. The facility comprises over 80,000 ft2 and employs 42 people.
Over the two year life of the facility, TXUP has maintained a good relationship with the surrounding community. TXUP is committed to the community of Mansfield, supporting local projects and activities as well as providing jobs at the plant.
The RMP regulated purification processes at TXUP include hydrochloric acid and ammonium hydroxide. For the covered processes, anhydrous hydrogen chloride and anhydrous ammonia are delivered, offloaded, and stored in a
n enclosure. The maximum inventory of the hydrogen chloride process is 110,000 pounds, and 43,000 pounds for ammonia hydroxide process. Both anhydrous hydrogen chloride and anhydrous ammonia are covered by EPA RMP since these chemicals are stored or processed in quantities greater than the Threshold Quantity (TQ) of 5,000 and 10,000 pounds respectively.
Worst-Case and Alternative Release Scenarios
The worst-case scenario as defined by the EPA, is an extremely unlikely event due to many factors, including the age of the process equipment, the prevention program, and the management system. The worst-case scenario for the TXUP facility is a 10 minute release of 110,000 pounds of anhydrous hydrogen chloride from storage. This includes administrative controls that limit the maximum allowable inventory for this storage vessel to 68% of the maximum capacity. In addition to controlling the maximum storage inventory, the tank is contained within a 68,500 ft3 enclosu
For this toxic material, a 10-minute gaseous release of the entire vessel contents is evaluated as required by EPA. The storage tank is in an enclosure that serves as a passive mitigation system, reducing the release rate to the atmosphere from 10,000 pounds per minute to 6,000 pounds per minute. In the worst-case analysis, TXUP's additional active mitigation systems including gas detectors, alarms, security cameras, and an emergency scrubber with an efficiency of greater than 80% cannot be accounted for when determining the consequence distance. This is done as required by the EPA.
The endpoint of concern is the hydrogen chloride gas concentration of 20 ppm. This endpoint is the Emergency Response Planning Guideline (ERPG) level 2 concentration developed by the American Industrial Hygiene Association (AIHA).
Since the worst-case scenario is an extremely unlikely event, TXUP has chosen to pursue the most realistic modeling to determine the potential consequence distance. The
DEGADIS model which was developed by industry with the support of the DOE and EPA is used. The distance to the 20 ppm endpoint is 5.2 miles. Within this vulnerability zone there are offsite public receptors including churches, schools, businesses, a nursing home, a hospital, a daycare center, a prison, and recreational public receptors. As indicated from 1990 census data, there are 18,000 residents within a 5.2 mile radius surrounding the facility. Only a small fraction of these individuals could potentially be impacted by even this worst-case scenario, as such a toxic release would travel in the direction of the wind.
The worst-case scenario--with a catastrophic release during the most pessimistic weather conditions--is not expected within the lifetime of the TXUP facility. Our management systems are in place and prevention programs are fully implemented to protect the public, our personnel and the environment.
Alternative Release Scenario
The "more likely" release, as defi
ned by the EPA, for the two covered processes is a leak in an offloading hose, and has been evaluated as part of the alternative release scenario analysis. Even though this scenario is considered to be the most likely to result in an offsite impact, TXUP has maintenance programs, supplier contracts, and mitigation in place to reduce the likelihood and consequence of any such release. Maintenance procedures require the inspection and pressure testing of all hoses before offloading. Contracts with the anhydrous hydrogen chloride and anhydrous ammonia suppliers require that all hoses are inspected and replaced on a regular basis. Mitigation systems include an enclosure, excess flow valves, check valves, gas detectors, alarms, security cameras, offloading supervision, and an emergency scrubber with an efficiency of greater than 80%. In addition, the basis for the scrubber design is the mitigation of a hose failure during offloading for each of the covered chemicals.
The scenarios mod
eled include a leak in the 1" diameter anhydrous hydrogen chloride transfer hose from a tank car to storage, and a leak in the 2" diameter anhydrous ammonia transfer hose from a tank truck to storage. If the hose leaked during offloading, there would be a release from the anhydrous hydrogen chloride railcar in one case or a release from the ammonia tank truck in the other. In both cases, the release would be inside of the specifically designed enclosure. Back flow from storage is not significant due to use of a check valve in the offloading lines to both storage tanks. The release rate is assumed to be just below the excess flow valve set point for each process--25 gallons per minute (gpm) for the hydrogen chloride process and 50 gpm for the ammonia process. The maximum duration to stop loss of containment from either process is 10 minutes.
For the hydrogen chloride hose leak, the release rate is 25 gpm (210 pounds per minute). The ammonia hose failure results in a release of
50 gpm (250 pounds per minute). Taking into account an enclosure and scrubber with 80% efficiency the final release rate to the atmosphere is 40 pounds per minute for a hydrogen chloride leak and 50 pounds per minute for an ammonia leak.
As discussed, passive mitigation for both covered processes includes a 68,500 ft3 enclosure. Active mitigation includes many features, and in particular a scrubber with greater than 80% efficiency. The scrubber vent is 38 inches in diameter and the exit point is located 34 feet above ground level. Upon gas detection in the enclosure the air flow rate through the scrubber is automatically increased from 2,500 to 22,500 cubic feet per minute (CFM). Since such a release would be vented through a scrubber with an efficiency greater than 80%, the toxic vapor (then present at low concentrations) would not behave as a dense gas.
The EPA OCA Lookup tables are used to determine the distance to the endpoint of concern. Since a leak in the offloading hose
is the "most likely" scenario for each covered process, TXUP chose to obtain conservative results for the potential hazard distance, for incorporation in the site's Emergency Response Plan.
For the "most likely" release scenarios, the distance to the hydrogen chloride 20 ppm toxic endpoint is 0.30 miles and the distance to the ammonia 200 ppm toxic endpoint is 0.20 miles. Within both of the vulnerability zones are homes and industrial public receptors, including a total of about 9 residents. The residential impacts were determined from a house count within the "vulnerability zone".
General Accidental Release Prevention Policies and Programs
The safety of onsite personnel, the surrounding community, and the environment is a priority with TXUP management. Before this facility was constructed, a preliminary Process Hazards Analysis (PHA) was conducted and comparisons made to a similar overseas facility to ensure that the new facility would be constructed and operated to minimize t
he risks associated with the storage, purification, and packaging operations at the new site. Since the preliminary PHA, TXUP has conducted a revised PHA and Pre Startup Safety Review (PSSR) of all purification processes.
Many of the processes, including the RMP covered processes are also regulated under the Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) regulation, 29 CFR Part 1910.119. The release prevention program at TXUP was developed to prevent onsite and offsite impacts to people and the environment. Therefore, this facility has developed a release prevention program to comply with both the EPA Risk Management Program (RMP) rule and the OSHA PSM requirements. The release prevention program includes the following elements: process safety information, PHA, operating procedures, training, mechanical integrity, management of change, PSSR, compliance audits, incident investigation, employee participation, hot work permits, contractors, and o
TXUP's primary focus is preventing accidental releases and spills. This is a new facility and as much the mechanical integrity of the processes is excellent. TXUP has inspection and preventative maintenance in place to maintain this high level of mechanical integrity. In addition to prevention, in the unusual case that a release or spill does occur, the TXUP facility incorporates numerous ways of containing it and mitigating any effects. These features include scrubber systems, double containment, emergency relief valves, an enclosure for anhydrous hydrogen chloride and anhydrous ammonia, gas monitors, and security cameras throughout the processes.
Employee training is also a major focus at TXUP. In addition, monthly safety meetings are held two times each month to ensure prompt communication and input from employees. New-hires also receive safety training during the first three days of the training program.
Five-Year Accident History
TXUP is a new facility and has o
nly been in operation for 8 months. There have been no releases of hydrogen chloride or ammonia in TXUP's eight months of operation.
Emergency Response Program
TXUP has developed an emergency response plan for the facility, and copies have been provided to the Mansfield Fire Department and the local hospital.
All operators at the TXUP facility receive 40 hour HAZWOPER emergency response training, and onsite emergency response drills are performed semi-annually. In addition, once per year, TXUP and the Mansfield Fire Department conduct a joint emergency response drill. The site maintains the necessary Personal Protective Equipment (PPE) for minor spills and events, and outside resources are used as needed.
If a release were to occur, members of TXUP management are on call to respond and direct the emergency response 24 hours per day, 365 days per year. TXUP's plan includes immediate contact of the Mansfield Fire Department. In addition, TXUP has contracted a specialist eme
rgency response firm, Eagle Construction & Environmental Services (based in Ft. Worth), to assist in an emergency. If evacuation of the surrounding communities is required, TXUP will notify the Mansfield Fire Department of the required evacuation zone. A one call system, donated to the Mansfield Fire Department by TXUP, will automatically notify residences and other public areas within the evacuation zone. If additional support is required, the Mansfield Fire Department will notify the Arlington Fire Department to dispatch their Hazardous Materials Response Team. In addition, a member of TXUP management will notify the National Response Center and the TNRCC to report the situation.
Planned Changes to Improve Safety
As this is a new facility, the most recent designs and technologies are already incorporated into our facility and operations. Yet, the direction of TXUP management is for continuous improvement.
Additional planned changes that will improve safety include continuous
updates to operating procedures, annual evaluation of PPE and continuing training for employees in the hazards of anhydrous hydrogen chloride, anhydrous ammonia and other hazards associated with the process at the TXUP facility. TXUP will also periodically update and improve its prevention program and process safety management system, and conduct additional evaluations as needed.