Star Field Services Co.--Clarkson Gas Plant - Executive Summary
The Clarkson Gas Plant produces natural gas liquids (NGL) from gas feed. The plant consists of a skid-mounted cryogenic unit, a deethanizer, a regenerator, and compressor engines. The facility is capable of processing up to 20 million standard cubic feet per day (mmscf/d) of natural gas; however, it currently only processes between 10 and 14 mmscf/d of natural gas and produces 200,000 barrels per year of NGL. The Clarkson Gas Plant is located in a remote area near the City of Sonora, Texas. The following is a summary of the facility's risk management program. |
1. ACCIDENTAL RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES
The Clarkson Gas Plant has a long-standing commitment to worker protection and public safety, as demonstrated through the accidental release and emergency response programs implemented at the Plant. These programs provide information regarding personnel training in accidental release and response procedures, process operations, and health and safety practices;
written operation and maintenance procedures for each process; hazard analysis and response; and hazard communication. It is the Star Natural Gas Company's (SNGC) policy to implement reasonable controls to prevent accidental releases of regulated substances, as well as train personnel to respond, control, and mitigate releases, if necessary.
2. FACILITY AND REGULATED SUBSTANCES
The Clarkson Gas Plant is designed to produce natural gas liquids (NGL). Dry, sweet, natural gas is received by pipeline and processed by a skid mounted cryogenic unit, which lowers the temperature of the natural gas to form NGL. The residue natural gas goes to a sales pipeline, and the NGL are stored on-site prior to being trucked to a sales point. Although the facility is capable of processing up to 20 million standard cubic feet per day (mmscf/d) of natural gas, it currently processes 10 to 14 mmscf/d of natural gas on an annual basis and produces 200,000 barrels per year of NGL.
Natural gas liqui
ds are the regulated substance that is processed and stored at the facility in amounts above the threshold limit. Approximately 200,000 bbls/yr of NGL is produced annually.
3. OFF-SITE CONSEQUENCE ANALYSIS RESULTS
The EPA-RMP*Comp Model was used to predict the worst-case and alternative release scenarios for flammable substances present at the Clarkson Gas Plant. Worst-case and alternative release scenarios for toxic substances were not determined due to the absence of threshold quantities of toxic substances.
The worst-case release scenario for a flammable substance is defined by the regulations as an instantaneous release of the flammable substance, in this case NGL, and a vapor cloud explosion. This scenario is based on the assumption that if the pressure of the tank is reduced as a result of the incident, the entire quantity of the flammable substance will vaporize. Therefore, the use of passive mitigation systems, such as storage tank cont
ainment dikes, are not applicable in this case, as liquids are not released. It is predicted that a worst-case release will have an off-site impact. The end point or point at which the vapor cloud is reduced to 1 psi overpressure is estimated to be at a distance of 0.3 miles from the Plant. SNGC maintains a series of safety devices on the system (e.g. high pressure alarms) which make it extremely unlikely that the worst case scenario would occur.
The alternative-case release scenario for flammable substances at the Clarkson Gas Plant consists of the rupture of the NGL pressurized storage tank. This scenario differs from the worst-case secnario in that it is assumed that a smaller volume of NGL is being stored in the tank and that this volume is released to the ground. Passive mitigation measures, such as the use of storage tank containment dikes, will contain the liquids, if present. However, in this case, it is assumed that the NGL will vaporize due to the a
bsence of adequate pressure and the vapors will ignite in a vapor cloud explosion or fire. The EPA-RMP*Comp Model determined that the end point or point at which the vapor cloud is reduced to Lower Flammable Limit is estimated to be at a distance of 0.1 miles from the Plant. The use of safety devices reduces the probability of the alternative-case scenario occurring.
4. GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAM AND CHEMICAL SPECIFIC PREVENTION
The Clarkson Gas Plant is subject to the requirements of the Occupational Safety and Health Administration's (OSHA) Process Safety Management (PSM) Standard. The practices employed at this facility which are most important to the PSM accident prevention program are described in more detail below. This accident prevention program is also applied to all RMP covered processes at the Clarkson Gas Plant.
Active employee participation and involvement in the development and implementation of the Clarkson Ga
s Plant's PSM program is an important step toward achieving the objective of preventing or minimizing the effects of catastrophic releases of toxic, reactive, flammable, or explosive chemicals. Employee involvement ensures that all perspectives regarding PSM are considered, and that the best ideas are implemented. Open communication is encouraged between supervisors and employees regarding all safety and health issues.
The Clarkson Gas Plant strongly promotes employee involvement in developing and implementing safety and accident prevention standards. Safety meetings, special training programs for emergency response and first aid, and hazard communication training are scheduled on a regular basis to ensure that employees are properly trained in health and safety issues and have the opportunity to voice their concerns regarding such issues. Employees are also encouraged to discuss safety and accident prevention practices with their supervisors if they have questions, comments, conc
erns, or suggestions.
Process Safety Information
The Clarkson Gas Plant maintains complete and accurate process safety information records concerning process chemicals, technology, and equipment. Technical documents describing process operations and process design and construction are available to all employees, including operators, Process Hazard Analysis (PHA) team members, training coordinators, contractors, pre-startup safety review team members, and emergency preparedness team members. These documents describe the properties and hazards of all process chemicals and include specific chemical inventories; the limits of key process parameters; and the equipment design basis/configuration including the materials of construction, design pressure and temperature ratings, and electrical ratings of equipment. This information, in combination with written safety procedures and trained personnel, provide the basis for developing and implementing all inspection and maintenance procedure
s, as well as evaluating proposed process and facility changes to ensure that safety features in the process are not compromised.
Process Hazard Analysis (PHA)
The Clarkson Gas Plant has developed a comprehensive program to help ensure that hazards associated with process operations are identified and controlled. In this program, each process is systematically examined to identify potential hazards and ensure that adequate controls are in place to manage these hazards should it become necessary. Process operations are evaluated using the what-if checklist method by a team of employees who are familiar with the operation and maintenance and the engineering specifications of each process. The team identifies the potential hazards associated with each process, evaluates the existing accident prevention and mitigation measures for each process, and makes recommendations for additional prevention and/or mitigation measures as necessary. The PHA team findings are then forwarded to manag
ement for resolution.
Implementation of the mitigation measures identified by the PHA team is based on the relative risk ranking assigned by the team. This risk ranking method ensures that potential accident scenarios with the highest risk receive immediate attention. All management-approved mitigation measures identified by the PHA team are tracked from start to finish. The final resolution of each PHA team finding is documented and retained in the PHA files.
The PHA team conducts a hazard analysis review every five years for the life of the process to ensure that the process controls and/or process hazards do not significantly deviate from the original design safety features. The results and findings of these PHA reviews are documented and retained in the PHA files and are forwarded to management for consideration. The final resolution of each PHA team finding is documented and retained in the PHA files.
The Clarkson Gas Plant maintains written operati
ng procedures for all process operations. These procedures include specific instructions and details pertaining to safety precautions, process hazards, and process operations. The operating procedures manual is written in a clear, concise tone so that it is applicable to both new and experienced operators.
The Clarkson Gas Plant has developed a comprehensive process operation and safety training program for its employees. New employees receive basic training in gas plant operations and safety at the time of hire. All other employees receive refresher training on process operations and safety on an annual basis to ensure that their skills and knowledge are maintained at an acceptable level.
The Clarkson Gas Plant has developed operation and safety procedures for contractors that work at the facility during periods of increased maintenance or construction. These procedures ensure that contractors perform their work in a safe manner; have the appropriate knowle
dge and skills to work on or near process equipment; are aware of the hazards of their workplace; understand the appropriate measures to take when hazards are encountered; understand and follow site-specific safety rules; and inform gas plant personnel of any hazards encountered during their work. This information is presented to the contractors during an orientation session that is conducted prior to the start of work. The orientation session also includes a review of process operations, safety and health hazards, emergency response plan requirements, and safe work practices.
Pre-startup safety review
The Clarkson Gas Plant conducts a pre-startup safety review (PSSR) of any new facility or facility modification that requires a change in process safety information. The purpose of the PSSR is to ensure that safety features, procedures, personnel, and equipment are appropriately prepared for startup prior to placing the equipment into service, that all construction is completed in ac
cordance with design specifications, and that all supporting systems are operationally ready. The PSSR involves field verification of the construction and serves as a quality assurance function by requiring verification that accident prevention program requirements are properly implemented.
The Clarkson Gas Plant has established practices and procedures for maintaining process equipment. The basic aspects of this program include employee training, a written process equipment maintenance manual, regularly scheduled inspections and tests of process equipment, the correction of any process equipment deficiencies as needed and within a timely manner, and the application of quality assurance measures in equipment purchases and repairs. In combination, these practices form a system that maintains the mechanical integrity of the process.
Safe Work Practices
The Clarkson Gas Plant has established safe work practices to ensure employee safety during process operation
and maintenance activities. These safe work practices include hot work permits and lock-out tag-out procedures. Training of affected personnel in these areas ensures that operation and maintenance activities are performed in a safe manner.
Management of Change
The Clarkson Gas Plant has established a comprehensive system to manage changes to all covered processes. This system requires that changes to items such as process equipment, technology (including process operating conditions) and procedures be properly reviewed and authorized by management prior to implementation. Changes are reviewed to ensure that adequate controls are in place to manage any new hazards and verify that existing controls have not been compromised by the change. Affected chemical hazard information, process operating limits, and equipment information and procedures are updated to incorporate these changes. Operation and maintenance personnel are then provided the necessary training on the change.
ddition to the accident prevention program requirements of the PSM program, the Clarkson Gas Plant has installed safety devices on process equipment in order to ensure the safe operation of all processes. These devices aid in the detection, containment and/or control, and mitigation of accidental releases of regulated substances within the facility. (Detection devices include process detectors and alarms; containment and/or control devices include process relief valves, isolation valves, automated shutdown systems for specific process parameters, atmospheric relief devices, and redundant equipment and instrumentation, such as an uninterruptible power supply for process control systems; and mitigation devices include fire suppression and extinguishing systems and personal protective equipment, such as chemical protective clothing and self-contained breathing apparatus). Collectively, these prevention program elements can help prevent potential accident scenarios that could be caused
by equipment failure and human error. SNGC will continue to monitor developments in safety devices and equipment to ensure that the Clarkson facility operates in the safest manner possible.
5. FIVE-YEAR ACCIDENT HISTORY
The Clarkson Gas Plant has an excellent record of accident prevention. Over the past five years, there has been only one minor incident at this facility. The incident occurred in August, 1996 and was caused by a tube that ruptured in the fired heater. A pressurized gas stream was released into the cabin of the heater, causing a gas vapor fire until gas source was shut-off. The incident lasted for about 30 minutes, and the responder was notified immediately. There were no on-site or off-site deaths or injuries during the incident. The faulty valve was replaced immediately after the incident for a cost of approximately $ 10,000.
6. EMERGENCY RESPONSE PROGRAM
The Clarkson Gas Plant maintains a written emergency response manual to provide employees with information
regarding worker protection and public safety, in the event of a fire or explosion caused by the accidental release of a flammable substance. The procedures address the notification of local emergency response agencies, post-incident cleanup and decontamination requirements, and employee training requirements. The emergency response manual is updated when modifications are made to the Clarkson Gas Plant facilities and changes are administered through the management of change process.
The emergency response program for the Clarkson Gas Plant has been developed to work in coordination with the Sutton County Sheriff Department and the Sonora Fire Department. Around-the-clock communications have been established between these departments and the Clarkson Gas Plant, as well as the appropriate local emergency planning commission (LEPC) officials and other emergency response organizations. Periodic meetings of the emergency response committee facilitate incident response and public not
Emergency drills are carried periodically as part of the ongoing training process. A post drill review is conducted to identify the strengths and weaknesses of the plan. Any areas that have been identified as needing improvement are then addressed, and the plan is modified. The modifications are then communicated to employees and outside agencies.