El Paso Field Services Dubach Gas Plant - Executive Summary
ACCIDENTAL RELEASE PREVENTION AND RESPONSE POLICIES |
The Dubach Gas Plant has a long-standing commitment to worker and public safety. This commitment is demonstrated by the resources invested in accident prevention, such as training personnel and considering safety in the design, installation, operation, and maintenance of the facility's processes. The El Paso Field Services (EPFS) policy is to implement reasonable controls to prevent foreseeable releases of substances.
DESCRIPTION OF THE STATIONARY SOUCE AND REGULATED SUBSTANCES
EPFS operates the Dubach Gas Plant located in Lincoln Parish, Louisiana. The location of the facility is illustrated on Figure 1, a 7.5 minute United States Geological Survey (USGS) map. The Dubach Plant is a cryogenic natural gas processing plant designed for the extraction of liquid (LPG) Y-grade product from a gas stream. The cryogenic extraction plant recovers ethane in addition to propane, butanes, and gasoline from the inlet gas. Mixed liquids pr
oduct from the liquids extraction plant is delivered via a pipeline. As evidenced in the ensuing text and based on criteria outlined in the Accidental Release Prevention Program (ARP), the Dubach Gas Plant is a Program 3 process.
The Dubach Gas Plant was evaluated to determine if any regulated flammable or toxic substances were present in the process and if they exceeded the threshold quantity. All equipment and vessels are considered to be connected and/or co-located; consequently, for the purposes of the ARP Program, all equipment and vessels are part of a single process. The identification of even a single vessel exceeding threshold quantities of a regulated flammable or toxic substance would subject a process to threshold determination for offsite consequence analysis.
EPFS identified three regulated flammable substances and zero regulated toxic substances along with the largest single vessel quantity stored. It was determined that a single vessel of flammable mixture (LPG)
exceeded threshold quantity. The identification of this exceedance indicates that the Dubach Gas Plant is a covered process with regulated substances subject to threshold determination for offsite consequence analysis. The other two flammable substances, natural gas and acetylene, are stored in vessels significantly smaller than the single largest vessel of flammable mixture (LPG).
OFF-SITE CONSEQUENCE ANALYSIS RESULTS
Worst-Case Scenarios (WCS)
The Environmental Protection Agency (EPA) has defined a worst-case release as "the release of the largest quantity of a regulated substance from a vessel or process line failure that results in the greatest distance to a specified endpoint." A WCS analysis is required for each toxic substance in a covered process while only one WCS analysis is required for regulated flammable substances as a class. WCSs are assumed to occur at ground level with meteorological conditions defined as atmospheric stability class F (stable atmosphere), wind s
peed of 1.0 meters per second (2.2 miles per hour), and an ambient air temperature of 25:C (770F). Topography for WCSs are distinguished between rural and urban.
Regulated flammable substances or mixtures containing flammable substances include both gases and volatile liquids. The WCS assumes that the total quantity of a vapor cloud is released and detonates. The endpoint for a WCS involving a regulated flammable substance or mixture is an over pressure of 1 pound per square inch (psi). For a regulated flammable substance, consequence distance determination is based on its heat of combustion. For regulated flammable mixtures, the component with the highest heat of combustion can be used for consequence distance determination or, if preferred, directly calculated using equation C-1 of the Offsite Consequence Analysis Guidance Document (OCAGD). The quantity of a regulated substance/mixture used to determine distance to endpoint is the largest quantity of a
regulated substance/mixture in a single vessel.
Flammable mixture is a mix of methane, ethane, propane, butanes, pentanes, and hexanes contained in a pressurized liquid storage vessel (vessel number SV18.01) having the capacity of approximately 30,000 gallons (122,800 lbs.). For the purpose of identifying the maximum release quantity for use in determining potential off-site impacts, it is assumed that the entire contents of the vessel is released to the atmosphere, forming a vapor cloud. Using the criteria outlined in the ARP rule, this mixture represents the facility's worst-case scenario for flammables.
Although methane was identified as having the highest heat of combustion (50,029 kjoule/kg) while acting only as a minor component, it was determined that its use would provide a more conservative consequence distance. The distance to the endpoint of 1 psi overpressure for the worst-case release of the flamm
able liquid mixture was calculated and determined to be 0.41 miles. The distance to endpoint is greater than the distance to public receptors. The Dubach Gas Plant is, therefore, classified as a Program 3 process under the ARP Program.
Toxic Liquids and Gases
Toxic gases include all regulated toxic substances that are gases at ambient temperature (temperature 25: C, 770F), even if they are stored as liquids under pressure or refrigeration. For the consequence analysis, a gaseous release of the total quantity is assumed to occur in 10 minutes, regardless of storage conditions. For toxic liquids, the total quantity in a vessel is assumed to be spilled onto a flat, non-absorbing surface. For toxic liquids carried in pipelines, the quantity that might be released for the pipeline is assumed to form a pool. Passive mitigation systems may be taken into account in consequence analysis for both toxic gases and liquids. The endpoint for air dispersion modeling to estimate the conseque
nce distance for a release of a toxic gas and liquid is presented for each regulated toxic gas and liquid in Appendix B of the OCAGD in Exhibits B-1 and B-2, respectively.
The Dubach Gas Plant does not have any toxic substances held above the threshold quantity. Analysis of one worst-case release scenario for each regulated toxic substances is, therefore, not required.
Alternative Release Scenarios (ARS)
An ARS describes an incident that is more likely to occur than those cited for a WCS. One ARS analysis is required for each listed toxic substance in a Program 2 or 3 process that exceeds threshold quantity while only one ARS analysis is required for all flammable substances as a class. For ARSs, both active and passive mitigation systems can be considered.
Alternative release scenarios for flammable substances should have the potential to cause substantial damage, including on-site damage. Alternative release scenarios for toxic substances should be those that lead to concent
rations above the toxic endpoint beyond the process fenceline. Those releases that have the potential to reach the public are of the greatest concern.
Dubach Gas Plant Alternative Release Scenario for Regulated Flammables
A single ARS for the flammable mixture is required under the ARP Program. A hypothetical, but likely to occur, release scenario has been identified for the flammable mixture as follows. Seal failure on the transfer pump causes a release from a one-inch opening at a pressure of 250 psig and a temperature of 1500F. The release is assumed to continue for ten minutes. The flammable mixture will vaporize and may ignite a vapor cloud explosion with an endpoint of 1 psi overpressure.
It was determined that a 10-minute release would involve 1615 pounds of the flammable mixture. Using the TNT equivalency formula from the OCAGD, it was determined that a release of this amount of a buoyant gas in a rural area would result in an ARS endpoint distance of 0.10 mil
Dubach Gas Plant Alternative Release Scenario for Regulated Toxics
The Dubach Gas Plant does not have any toxic substances held above the threshold quantity. Analysis of each regulated toxic substance is, therefore, not required.
FIVE YEAR ACCIDENT HISTORY
The Dubach Gas Plant has not had any accidental releases during the past five years that meet the criteria for an accidental release as discussed in 40 CFR 68.42.
LOCAL EMERGENCY RESPONSE COORDINATION
The Dubach Gas Plant has coordinated its emergency response activities with the local emergency planning and response agencies as required in 40 CFR 68,12(b)(3).
GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAM
The following is a summary of the accident prevention program in place at the Dubach Gas Plant. Because plant processes are subject to EPA's RMP regulations and to OSHA's PSM standards, this summary addresses each of the OSHA PSM elements and describes the management system in place to implement the accident preven
EPFS and the Dubach Gas Plant actively encourage all levels of employees and contract employees to participate in creating a safe work environment. This participation begins with well established mechanisms of communication with all employees regarding covered process information. Employees are involved in maintaining PSM rule compliance based on their knowledge, skill, job responsibilities, and experience. Specific ways that employees can be involved in the accident prevention program are documented in an employee participation plan that is maintained at the plant.
Process Safety Information
The Dubach Gas Plant maintains written information intended to provide a foundation for identifying and understanding the process hazards. This information addresses chemical properties, inventories, and associated hazards, as well as for key process parameter limits and equipment design basis/configuration information. Specific departments within t
he plant are assigned responsibility for maintaining up-to-date process safety information.
Chemical-specific information, including exposure hazards and emergency response/exposure treatment considerations, is provided in the material safety data sheets (MSDSs). This information is supplemented, when required, by documents that specifically address known corrosion concerns and any known hazards associated with the inadvertent mixing of chemicals. In addition, the plant has documented safety-related limits for specific process parameters and ensures limit maintenance by using highly trained personnel, process controls, and monitoring and protective instrument systems.
The plant also maintains documentation that provides information about the design and construction of process equipment. Equipment information includes construction materials, design pressure, and temperature and electrical ratings. EPFS utilizes Job Book Procedures for pumps, controls and relief valves, API Stand
ards for pipe, vessels, and tanks, and ANSI Standards for the ESD System. This information also provides a basis for establishing inspection and maintenance activities, as well as for evaluating proposed process and facility changes to ensure that safety features in the process are not compromised.
Process Hazard Analysis (PHA)
The Dubach Gas Plant has a comprehensive program to help ensure that hazards associated with the various processes are identified and controlled. Within this program, each process is systematically examined to identify hazards and ensure that adequate controls are in place to manage these hazards.
The Dubach Gas Plant primarily uses the hazard and operability (HAZOP) study to perform these evaluations. A HAZOP uses a highly structured approach where process parameters such as flow and temperature are examined for deviations from their intended design. Deviation effects are considered in order to determine resulting potential hazards while preliminary reco
mmendations for improvement are proposed. The Dubach Gas Plant may also use what if analysis. This process utilizes questions that postulate mistakes in operations or failures of equipment. Based on the answers to the questions, consequences and preliminary recommendations can be determined.
The PHA team findings are promptly and systematically addressed. The Dubach Gas Plant assures that the recommendations are documented and resolved in a timely manner. This documentation includes the actions to be taken and a written schedule of completion dates. The plant also provides proof of communication with operating, maintenance, and other employees whose work assignments are in the process and who may be affected by the recommendations.
To help ensure that the process controls and/or process hazards do not eventually deviate from the original design safety features, the plant periodically updates and revalidates the hazard analysis results. These periodic reviews are conducted at
least every five years by the PHA team.
The Dubach Gas Plant maintains written procedures that address various modes of process operations, such as (1) initial startup, (2) normal operations, (3) temporary operations, (4) emergency shutdown, (5) emergency operations, (6) normal shutdown, and (7) startup following a turnaround or after an emergency shutdown. These procedures can be used as a reference by experienced operators and provide a consistent training basis for new operators. Operating procedures are periodically reviewed and certified as current. When a process change occurs, operating procedures are revised as necessary through the management of change process.
To complement the written process operation procedures, the Dubach Gas Plant has implemented a comprehensive training program for all employees. New employees receive job specific basic training in plant operations. Employee training includes emphasis on safety and health haz
ards, emergency shutdown operations, and safe work practices. Operators demonstrating adequate knowledge to safely perform duties and tasks are allowed to work independently.
Hot Work Permit
The Dubach Gas Plant issues a hot work permit for all hot work operations conducted on or near a covered process. Procedures for issuing a hot work permit are clearly outlined in the EPFS Safety Manuel. The Dubach Gas Plant provides Hot Work Permit training to all plant employees. Copies of issued work permits are maintained in Operations and Maintenance for a period of 1 year following completion of work.
The Dubach Gas Plant periodically uses contractors to perform maintenance or repair, turnaround, major renovations, or specialty work on or adjacent to a covered process. Because some contractors work on or near process equipment, the plant has procedures in place to ensure that contractors (1) are trained in the work practices necessary to safely perform his/her job, (2) hav
e received and understood the training required and carry a training document card while on location, (3) follow the safety rules of the location including the safe work practices, (4) advise the plant of any unique hazards presented by the contractor, and (5) notify the facility of all illnesses and injuries that occur in the process areas.
Pre-Startup Safety Reviews (PSSRs)
The Dubach Gas Plant conducts a PSSR for any facility modification that requires a change in the 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. This review provides an additional check to make sure that construction and equipment are in accordance with design specification, that adequate safety, operating, maintenance, and emergency procedures are in place, and that training of each employee involved in operating the process or equipment has been com
pleted. A standard checklist is used to document compliance.
The Dubach Gas Plant has well-established programs, procedures and practices that are required to ensure that equipment used to process, store, or handle lightly hazardous chemicals and/or flammable gas or liquid is designed, constructed, installed, and maintained to minimize the risk of a release. Equipment examples include vessels, storage tanks, piping systems, and relief and vent systems with associated emergency shutdown systems and controls (i.e., monitoring devices, sensors, alarms, and interlocks).
Maintenance personnel receive training on (1) an overview of the process, (2) a review of the process hazards, and (3) the procedures applicable to the employee's job tasks to ensure that the employees can perform the job tasks in a safe and satisfactory manner. Process equipment inspection and testing follows recognized and generally accepted good engineering practices. Equipment deficiencies that
are outside of acceptable limits are corrected before further use or in a safe and timely manner when necessary means are taken to ensure safe operation.
Management of Change
The Dubach Gas Plant has a comprehensive system to manage and document changes to all covered processes. A systematic approach is followed to control and manage facility changes in order to minimize the possibility that such changes will have an adverse impact on personnel safety, equipment, or the environment. Employees involved in process operations and maintenance and contract employees whose job tasks might be affected by process changes are informed of and trained in the change prior to process start-up.
The Dubach Gas Plant promptly investigates all incidents that resulted in, or reasonably could have resulted in, a fire/explosion, toxic gas release, major property damage, environmental loss, or personal injury. An incident investigation is initiated as promptly as possible to
thoroughly investigate and analyze the incident. This investigation is lead by an incident investigation team consisting of those with appropriate knowledge and experience in the process. The findings and recommendations made by the incident investigation team are promptly addressed and resolved in a timely manner. The final resolution of each finding or recommendation is documented, and the investigation results are reviewed with all employees (including contractors) who could be affected by the findings.
Emergency Planning and Response
The Dubach Gas Plant retains a written site specific formal emergency response plan which includes the designated actions the company and all personnel will take to ensure personal safety from fire and other emergencies. The plan outlines actions that company technicians and contract employees are to take when there is an unwanted release of highly hazardous chemicals. The intent of this plan is to facilitate the prompt evacuation of employees
when necessary and to account for all personnel. The emergency plan also includes procedures for handling small releases.
To help ensure that the accident prevention program is properly functioning, the Dubach Gas Plant periodically conducts an audit to determine whether the procedures and practices required by the accident prevention program are being implemented. Compliance audits are conducted at least every 3 years. The audit team includes those knowledgeable in the process, operations personnel, and at least one person trained in audit techniques and practices. The audit team develops findings and corrective actions are tracked until they are complete. The final resolution of each finding is documented, and the two most recent audit reports are retained.