Des Moines Metro. Wastewater Reclamation Facility - Executive Summary
Executive Summary |
Introduction and Background
The USEPA's Clean Air Act Amendments of 1990 included provisions that require facilities that use certain substances to develop a plan to reduce the likelihood of an accidental release of the substances to the atmosphere and reduce the likelihood of serious harm to the public and the environment. The plan must also include mitigation measures to reduce the potential impact on the public in the unlikely event of a release. The requirements of this plan, commonly referred to as a Risk Management Plan (RMP), are detailed and codified in 40 CFR Part 68.
The Des Moines Metropolitan Wastewater Reclamation Authority's (WRA) Wastewater Reclamation Facility (WRF) stores chlorine, sulfur dioxide, and digester gas (methane) in quantities above the regulatory thresholds at which a RMP/PSM is required. Chlorine is used to disinfect the wastewater effluent, and sulfur dioxide is used to remove chlorine residuals before the effluent is discharged to recei
ving water. Digester gas is a byproduct of the biosolids stabilization process and consists of primarily methane and carbon monoxide.
The RMP/PSM consists of three compliance programs, each with progressively stricter compliance standards. The chlorination, dechlorination, and digester gas processes at the WRF are subject to Program 3, the most stringent of the three programs, because the WRF is subject to the OSHA Process Safety Management (PSM) Standards and a worst-case release of chlorine, sulfur dioxide, or digester gas could affect the public.
The RMP/PSM consists of three major parts. The first part is the Hazard Assessment. The Hazard Assessment is done to determine the effects that a release of a regulated substance could have on the public. The results of the Hazard Assessment can be found in the Phase Two Report-Offsite Hazard Assessment that was prepared for Des Moines Metropolitan Wastewater Reclamation Authority (October 1998). The second part is a Prevention Program that
consists of 12 elements designed to improve the system safety and decrease the likelihood of a release. The third part is the Emergency Response Program, which develops a plan for dealing with a release in the unlikely event that one would occur. Because the regulations are very similar, the Prevention Program and the Emergency Response Program also serve as the OSHA PSM plan, and this document is therefore is referred to as the RMP/PSM plan.
As part of the RMP, a submittal to the USEPA is required. The submittal is referred to as RMP/PSM Submit and is included in Appendix D.Hazard Assessment
A Hazard Assessment was performed to determine the effects a release would have on the public. For chlorine and sulfur dioxide, the distance a set endpoint concentration of the gas would travel must be determined. For digester gas, the effects of an explosion must be determined. In addition, an estimate of the population that could be affected by a release of chlorine, sulfur dioxide, or digester
gas was determined, and sensitive receptors such as hospitals, schools, and nursing homes were identified. The Hazard Assessment considers two release scenarios-a "worst case" and an "alternative case."
The regulations require the development of a worst-case release scenario based on conservative assumptions. For example, it is required to assume that the entire contents of the largest single container of chlorine or sulfur dioxide will be released over 10 minutes. This is unlikely to occur since the properties of chlorine and sulfur dioxide would cause a freeze and thaw cycle to occur at the leak, which would slow the release. In addition, only "passive" mitigation methods such as buildings or dikes can be considered when determining the distance the release could travel. Passive mitigation, as defined, requires no mechanical, electrical, or human input. However, in many scenarios mitigating the release by isolating the process could reduce the amount released. I
n addition, the worst-case scenario requires that conservative atmospheric conditions be assumed which results in a large area of impact.
The hazard assessment requires that the "toxic endpoint" or distance from the point of release to a location at which the chemical concentration equals or exceeds a certain concentration must be determined. That concentration is defined as the maximum airborne concentration below which individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects, or symptoms that could impair an individual's ability to take protective action. Because the cloud from a chlorine or sulfur dioxide leak would disperse relatively quickly, an individual at a toxic endpoint would be exposed to the exposure limit concentration for much less than the 1 hour assumed by the limit. In addition, the exposure limit concentrations result in relatively minor health effects. Therefore, an individual at the toxic endpoin
t would be affected less than the results of the worst-case scenario may imply.
For the digester gas worst-case scenario, it must be assumed that all the gas in the vessel containing the largest quantity of digester gas is catastrophically released, and the gas is ignited and explodes. This is very unlikely to occur since the proper mixture of methane and oxygen required for an explosion would be difficult to achieve. The distance to the end of the impact zone for a digester gas explosion is defined by "1-psi overpressure." The 1-psi overpressure is the outside of the explosion shock wave, along which broken glass and other similar structural damage is possible.
The RMP rule also requires that at least one alternative release scenario be evaluated for sulfur dioxide, digester gas, and chlorine. The alternative scenarios reflect a type of release that is more likely to occur compared to the worst-case scenario. Unlike the worst-case scenario, the alternative release
scenario may consider "active" mitigation such as shutoff valves and a more realistic release quantity and release rate. Active mitigation is defined as requiring mechanical, electrical, or human input. Lastly, it assumes local, typical meteorology, which is more realistic than the conservative meteorological conditions that must be assumed for the worst-case scenario. The alternative release scenario for chlorine and sulfur dioxide was a release of chemical through an evaporator pressure release valve. The alternative release scenario for digester gas was a flame-out and subsequent ignition of the digester gas flare. These alternative release scenarios are considered to be more representative of the effects likely in the event of a release.Prevention Program
The Prevention Program, together with the Emergency Response Program, make up the RMP/PSM. The Prevention Program consists of 12 elements designed to improve the system safety and decrease the likelihood of a release.
The participation of the Des Moines WRF staff in preparing the RMP/PSM program was critical to the program's successful implementation. Employee participation is valuable because it increases the safety awareness of the staff and it allows the staff's experience in operating and maintaining the processes to be incorporated into the plan.
WRF staff participated in the development of the Prevention Program through a series of meetings and workshops. Another way that the WRF staff participated in the development of the RMP/PSM was the Process Hazard Analysis that is described below. All WRF staff received RMP/PSM awareness training that instructed staff on how the RMP/PSM requirements may impact their jobs. Staff who operate and maintain the RMP/PSM processes were trained in how to safely maintain and operate the processes.
Process Safety Information
The RMP regulations require that information concerning process chemicals, technology, and equipment be compiled as part of a RM
P program. Emergency response planners can use such information to develop training programs and procedures, or as a general resource. The information will be supplied to contractors who will work in the chlorine, sulfur dioxide, and digester gas process areas as part of the requirements outlined in the Contractors element. All the required process safety information was compiled as required by the RMP regulations. The information meets and in many cases exceeds the minimum required by the regulations.
Process Hazard Analysis
A process hazard analysis (PHA) was conducted systematically to evaluate potential causes and consequences of accidental releases. This information was used by WRF staff to improve safety and reduce the consequences of accidental releases. Equipment, instrumentation, utilities, human actions, and external factors that might affect the process were the focus of the PHAs that were performed for the chlorine, digester gas, and sulfur dioxide processes.
The chlorine a
nd sulfur dioxide PHAs were conducted by an interdisciplinary team of WRF staff familiar with the process operation and maintenance and plant management. The PHA was done using a combination of "What-If" and "Checklist" methods. Based on the results of the PHAs, numerous changes in operating, maintenance, and other process safety management procedures that would improve the overall safety of the WRF were identified. The changes that most affect the severity and likelihood of a release have been adopted by the WRF and incorporated as part of the overall Process Safety Management Program. The other improvements and process modifications to reduce or eliminate potential hazards are scheduled to be implemented or incorporated.
Operating procedures for the chlorination, dechlorination, and digester gas processes have been developed as part of the RPM/PSM. Written operating procedures assure continuous, efficient, and safe operation of the facility. The goal of the opera
ting procedures is to provide clear instructions to safely operate the process. Operating procedures are also used to train new employees and to provide refresher training for existing staff.
The detailed operating procedures include startup, shutdown and emergency operating procedures. The procedures describe how the system should be operated in order to minimize the chances of an accidental release. The procedures also emphasize safety considerations during operation and address hazardous situations that can occur and how to correct them.
An effective RMP/PSM training program can significantly reduce the number and severity of accidental release incidences. Employees involved in operating or maintaining the chlorination, dechlorination, or digester gas processes must receive training that includes applicable operating and maintenance procedures and an overview of the process. Training must emphasize safety and health hazards and safe work practices.
Des Moines WRF staff have
received initial training on the operations and maintenance of the regulated processes, an overview of each of the RMP/PSM plan elements, and the procedures that must be followed to comply with the requirements of the RMP/PSM plan. In addition to RMP/PSM plan training, select WRF staff have been trained to respond to an accidental release. Refresher process operation training must be provided at least every 3 years. Refresher training for emergency response is conducted annually.
The WRF must make contractors aware of the known hazards of the chlorine, sulfur dioxide, and digester gas processes related to the contractors' work. In addition, the WRF must make contractors aware of the applicable elements of its emergency response plan. The WRF should screen contractors for ones who can perform work on or adjacent to the chlorine, sulfur dioxide, and digester gas processes without compromising the safety and health of employees at the facility. "Adjacent" in this case is defi
ned as working closely enough to a covered process so that the contractors' work could reasonably be expected to potentially affect process safety or to potentially cause, either directly or indirectly, an accidental release.
Before allowing a contractor to work on or adjacent to the chlorine, sulfur dioxide, or digester gas processes, the WRF must obtain and evaluate information regarding the contractor's safety performance and programs. When a contract involving work on or adjacent to the chlorine, sulfur dioxide, or digester gas processes is to be bid, the bidding procedures must ensure that contractor safety management requirements are met. If a contractor is to work in or adjacent to any covered processes, a safety briefing, to make the contractor aware of the WRF's RMP/PSM plan requirements, must be conducted before work begins. Upon arriving at the plant for the first time to perform work, the contractor will be presented a Contractor Safety Management Briefing Form that must be
read and signed. All contractors should receive a Chlorine/Sulfur Dioxide Leak Response Protocol (Figure 12-1).
A pre-startup safety review must be conducted for any new covered process or for significant modifications to the existing chlorine, sulfur dioxide, or digester gas processes that necessitate a change in the process safety information. No new or significantly modified process will start up and no acutely hazardous chemicals will be introduced into such a process prior to the pre-startup safety review. The purpose of the pre-startup safety review is to ensure that the facility is ready to operate new and modified regulated processes safely.
To initiate the pre-startup safety review, all updated elements of the Process Safety Management Plan are assembled for review. This includes all process safety information, process hazard analysis, operating procedures, employee training and mechanical integrity. A pre-startup safety review team completes a pre-startu
p checklist. The pre-startup safety review team should complete and sign a Pre-startup Safety Review Form. This form documents the process, and helps ensure that the review has been properly performed. The Pre-startup Safety Review Form must be authorized before startup.
An effective mechanical integrity program is one of the primary lines of defense against a release. The mechanical integrity program also addresses equipment testing and inspection, preventative maintenance schedules, and personnel training. The intent is to ensure that equipment used to process, store, or handle chlorine, sulfur dioxide, and digester gas is maintained and installed to minimize the risk of releases.
The WRF maintenance staff use a computerized maintenance management system (CMMS) to store equipment information, generate and prioritize work orders, schedule preventative maintenance (PM), provide safety procedures for work orders, and maintain an inventory of parts and materials. The
CMMS system is used to generate work orders for preventative maintenance. In addition to preventative maintenance, the WRF staff performs corrective maintenance in the event of equipment malfunction or breakdown. Work orders indicate what safety precautions must be followed including whether lockout/tagout or confined space entry provisions are applicable. The staff that carryout maintenance are all trained as part of the RMP/PSM.
Hot Works Permits
RMP/PSM regulations require employees and contractors to employ safe work practices when performing "hot work" in, on, or around the chlorine, sulfur dioxide and digester gas processes. To ensure that hot work is done safely, a Hot Work Permit Program has been developed that requires a permit to be issued before hot work is performed. Hot work is defined as the use of oxyacetylene torches, welding equipment, grinders, cutting, brazing, or similar flame- or spark-producing operations.
The process of completing the hot work permit makes it ne
cessary to identify the hazard, recognize what safeguards are appropriate, and then initiate the safeguards necessary to ensure a fire-safe workplace. Following the standards outline in this section aid in complying with the OSHA Hot Works Regulations (1910.252(a)).
Management of Change
A system for the proper management of changes and modifications to equipment, procedures, chemicals, and processing conditions is required under the RMP/PSM. Modifications to the chlorine, sulfur dioxide, or digester gas system will be reviewed before they are implemented to determine if the modification would compromise system safety. An effective change management system will help minimize the chance for an accidental release.
If a modification covered under RMP/PSM is made, its effects must be addressed, employees must be informed, and the written procedures must be updated. The intent is to require that all modifications to equipment, procedures, and processing conditions other than "replacement in
kind" be managed by identifying and reviewing them before implementation. A Management of Change Committee will evaluate any modifications that are covered under the RMP/PSM. The Management of Change Committee will complete a Management of Change Form that the Plant Administrator will review and authorize prior to initiation of a covered change.
Each incident that resulted in or could reasonably have resulted in a catastrophic release of chlorine, sulfur dioxide, or digester gas must be investigated. A process to identify the underlying causes of incidents and to implement procedures for preventing similar events has been developed. To investigate an incident, an investigation team will be established. As part of the investigation, an incident report will be prepared to recommend system changes.
The investigation team should ask questions such as what equipment failed, which behavior failed, and which material leaked, reacted, or exploded? As part of the incident
review, staff actions that may have contributed to the incident will also be reviewed. A determination will be made as to whether it is necessary to institute additional training for the employees to prevent the incident from occurring in the future. On the incident report form, the Plant Administrator identifies which of the recommended system changes are approved for implementation. The incident investigation report and any changes resulting from the report will be reviewed with all staff members who operate and maintain the applicable system.
The Des Moines WRF is required to complete a compliance audit for the RMP/PSM program. The primary goals of conducting an internal compliance audit are to gather sufficient data to verify compliance with RMP/PSM requirements and good process safety practices, identify process safety deficiencies and develop corrective actions, and increase safety awareness among plant staff.
The compliance audit methodology is modeled after O
SHA's guidelines for conducting regulatory PSM compliance audits: Compliance Guidelines and Enforcement Procedures, OSHA Instruction CPL 2-2.45A (September 28, 1992). An internal compliance audit must be conducted at the plant at least once every 3 years for the chlorine, sulfur dioxide, and digester gas processes. A team that includes at least one person knowledgeable in the covered processes and an audit leader knowledgeable in RMP/PSM requirements and audit techniques will conduct the audits. The Plant Administrator and the audit team will promptly determine an appropriate corrective action for each deficiency identified during the audit and document the corrective actions and the dates by which they must be taken.
Emergency Response Program
The Emergency Response Program develops a plan for dealing with a release. OSHA Process Safety Management regulation 29 CFR 1910.119(n) and EPA RMP regulation 40 CFR 68 Subpart E require that an Accidental Release Emergency Response Plan be prep
ared. The plan must be prepared in accordance with the provisions of another overlapping OSHA regulation-Employee Emergency Plans (29 CFR 1910.38(a)). In addition, provisions of the OSHA hazardous waste and emergency response standard, 29 CFR 1910.120 (q), must also be considered. The Emergency Planning and Response Plan described in this section complies with the requirements of 40 CFR 68.95, 29 CFR 1910.38(a), and 29 CFR 1910.120(q).
The Emergency Planning and Response plan provides specific emergency response procedures for accidental releases of chlorine, sulfur dioxide, or digester gas. The emergency response procedures cover a release from the initial alarm stage through either leak stoppage or Hazmat assistance. As part of the emergency response procedures there are plans for victim rescue, leak investigation, and communication with additional support agencies. In addition, critical plant operations are identified to insure that, if possible, the critical WRF functions are kept
operational. The Emergency Planning and Response plan also indicates the level of training need to carryout the emergency response procedures. Only personnel trained at the Hazardous Materials Technician Level can attempt to stop a leak. The emergency response procedures refers to "Des Moines Metropolitan Wastewater Reclamation Facility Emergency Response Plan" in cases when plant evacuation is necessary.
Information regarding self contained breathing apparatus is also provided in the Emergency Planning and Response plan. It also addresses plant site communication, emergency response equipment, first aid and medical treatment, medical surveillance and consultation, and emergency response drills.