Y. Nimrod, Yaron Nimrod Engineering Consulting, Gilon, Israel
A fire incident in an oil refinery or petrochemical plant can be a very frightening event—the vast flames, the noises, the smells, and the feeling that at any moment, everything might explode. Operators, by their job definition, are required to suppress their natural reaction to run for their lives and remain at their posts and make every effort to take control of the event to the best of their abilities. This article presents a toolbox to help operators manage emergency incidents professionally and effectively.
Managing an emergency event in a petrochemical facility differs from a fire in a residential building due to the presence of large quantities of hazardous and flammable materials. In addition to basic firefighting and rescue operations, it is also essential to carry out actions to isolate the fire incident area from fuel and energy sources, reduce the fire intensity and prevent secondary events (i.e., the domino effect). These operations are outside the scope of the firefighting and rescue teams' skills.
Only those responsible for day-to-day operations and those familiar with the location and function of every piece of equipment and valve would know how to perform a "process extinguishing" of the fire, which is the most effective type of extinguishing.
Only experienced operators familiar with the facility will be aware of the risks close to the fire area, such as liquefied petroleum gas (LPG)-containing vessels that might fail [creating a boiling liquid expanding vapor explosion (BLEVE) hazard], fin-fan coolers that may increase the height of the flames, pipes that might undergo heating without enough room for thermal expansion, etc.
The main responsibilities of the operations teams in handling emergency incidents include:
Sounding the alarm and initial reporting. When sounding the alarm by dialing the plant's emergency number, it is essential to give a brief report that includes critical information such as:
Examples of such a report might include:
After receiving an accurate report, firefighters, paramedics and security personnel can know where to go, on what route, what tools to bring with them, which equipment they would need to operate (high-pressure pumps, foam dosing tanks, SCBA, etc.), whether road closures and restriction of access are required, and reporting to external parties.
For plants with a central control room, rather than assigning the job of alarming and reporting to the board operator of the unit where the incident occurs, it is more helpful to give that task to an operator in their vicinity whose units are unaffected.
After alerting the emergency services, informing other parties about the incident is crucial. This begins with reporting up the command chain—to a Shift Supervisor or Operations Manager—and alerting other process units' teams, especially those units feeding the unit where the incident occurred and units that are dependent on the proper operation of the damaged facility.
Locating personnel. In the heat of an emergency event, people tend to forget that the most important goal is saving human lives. In numerous emergency events, locating employees was not the first priority of the responding operators—sometimes, this ended in disaster.
During regular unit operation, the shift manager (or foreperson) must always be aware of the people who are present on the facility's premises and their general location. For this purpose, the shift team and other employees or visitors who come to the facility at routine times must be accustomed to some basic rules:
When an emergency incident occurs, after sounding the alarm, the shift manager must locate all employees in the facility and report missing persons and their approximate locations to firefighting forces.
The natural tendency of operators is to immediately perform actions to mitigate the incident, open firewater monitors, etc. Training is required to get the staff accustomed to remembering, first of all, to ensure that all personnel on the premises of the process unit are accounted for.
Initial activation of firefighting equipment. Oil refineries and petrochemical plants have many means of extinguishing fires, both fixed and portables. Rapid activation of extinguishing devices may lead to quickly overcoming a fire event before it develops into a significant one.
The decision of what means to use and whether to do so before or in parallel with other emergency operations is at the discretion of the senior person in the field—usually the shift manager (foreperson)
In the event of a fire caused by an uncontrollable gas burst, it is inadvisable to extinguish it before the leak can be stopped for fear of an explosion. Efforts must be made not to splash a large amount of water on very hot pipes and equipment to avoid thermal shock and quenching of the steel that could cause it to become brittle.
The shift manager and field operators must be skilled in choosing the correct fire extinguishing devices for the event and operating them [e.g., monitors, carbon dioxide (CO2) fire extinguishers, flood systems]. Acquiring and maintaining these skills requires fire extinguishing refresher training that the facility manager must initiate.
Care must be taken not to "get stuck" with firefighting operations and to transfer responsibility for them to the firefighters as soon as possible. Field operators have many other functions and responsibilities during an emergency incident, and standing in one place for a long time holding a fire hose is not the best use of their time and skills.
Shutting down the plant and isolating the affected area from fuel and energy sources. During a significant event that cannot be "surgically" isolated, the operations team must not hesitate to perform an emergency shutdown of the facility, including closing all pumps and compressors and shutting down all fired and electrical heaters. As simple and logical as this notion sounds, operators are often reluctant to initiate a plant shutdown even if it is obvious that there is no way to overcome the incident without shutting down the unit. It is often a weak point that must be discussed with operators during their refresher training.
The most efficient and effective way to control fire or release of process fluid in a process facility is by reducing the rate at which the material breaks out until it stops completely. As long as we "add oil to the fire," the fire will only intensify and the event might spread to other areas.
It is essential to try to pinpoint the bursting point as accurately as possible, although this is not always an easy task. If the location of the burst has been identified, it is crucial to stop the operation of the pressure source of fluid that is flowing to the point and close valves as close as possible to the bursting location. Such sources might be pumps, compressors and pressurized liquid or gas supply lines. Utilizing the control room as much as possible to perform the disconnection tasks using remotely operated valves and switches is preferable. At the plant's central electrical substation—or the local motor control center (MCC) of the process area, an onsite building where electrical equipment such as transformers, switchboards and motor control boards are located—there should be the possibility of cutting off power to selected motors or entire process areas, if necessary.
Adding heat from an external source into the damaged sector is similar in effect to adding fuel material. Therefore, it is also essential to omit heat sources, such as tower reboilers, steam-heated heat exchangers, electric heaters, etc. Again, it is worth using the control room to remotely shut down heat sources.
Even after an emergency shutdown of the process unit has been performed, it is important to isolate the affected area in a volume as small as possible to diminish the magnitude of the burst in a shorter time frame.
Emptying process vessels of flammable liquids (excluding LPG and its components) should be considered by pumping out liquids from the affected system after ensuring the closure of all pathways returning to the affected area (e.g., an overhead receiver pump that sends the overhead product to the top reflux line as well as to the product line).
Care must also be taken to avoid pumping liquids through pipes that pass through the area under direct fire or heat radiation. When it is impossible to get close to the epicenter of the incident, the disconnection can be carried out at the facility's battery limits valve stations or by using offsite isolation valves.
FIG. 1 shows a simplified flow diagram of a reaction section in a vacuum gasoil (VGO) hydrotreating unit.
Heavy vacuum gasoil (HVGO) is pumped through heat exchangers to a charge heater, which is also used to heat the recycle gas, which consists mainly of hydrogen. The hot HVGO and hydrogen (H2) enter a fixed-bed reactor where sulfur is removed from the HVGO and combined with H2 to produce H2S. Next, the reactor effluent stream flows to heat exchangers to preheat the HVGO and the recycle gas and then flashes into gas/liquid separators. Finally, the treated HVGO flows to a fractionation section, and the gas is recycled after passing through an amine scrubber to remove H2S.
FIG. 2 shows a release of process fluids from one of the feed/effluent exchangers, which operate at 48 barg and 330°C on the shell side, and 40 barg and 410°C on the tube side. Recommended isolation points are shown as red valves that should be closed to isolate the smallest possible volume around the burst-out point. The relevant battery limit valves should also be closed. Pressure sources (i.e., the charge pump and H2 compressors) must be shut down, as well as the external heat source (i.e., the fuel to the charge heater).
Releasing pressure from a leaking or breached system. The most efficient and effective way to assume control of a fire or breakout of fluid in a process facility is by reducing the rate at which the material breaks out until it stops completely. The breakout rate, of course, depends on the pressure difference between the inside of the system and the atmosphere.
In a large system or a high-pressure section, even after it is disconnected, it is inadvisable to wait for the pressure inside the system to be released through the breakout point. Therefore, simultaneously or immediately after isolating the system from its surroundings, pressure should be quickly released from the affected sector to a safe destination.
The most straightforward pressure release destination is towards the plant's flare. In most refineries and petrochemical plants, pressure may be released to the flare through control valves or manual valves—such as a relief valve’s by-pass line—from various sectors. Of course, the capability of the flare lines to deliver the gas being released must be considered, and care must be taken not to send a significant amount of liquids along with the gas. Additionally, the operators responsible for operating the flare must take care of efficient and smokeless combustion.
Pressure release towards the plant's fuel gas header, if such a possibility exists, is a limited and problematic solution and must be done gradually so that the pressure control system of the fuel gas header prevents critical shocks in the supply pressure to consumers.
In process units with high-pressure vessels with thick walls, sudden decompression should be avoided as much as possible. Therefore, it is worth studying in advance the instructions of equipment manufacturers to avoid causing long-term damage.
In systems containing LPG components, the release of pressure should be done only after applying judgment, since the decreased pressure will cause increased evaporation of LPG while cooling the equipment to extremely low temperatures and creating a risk of brittleness. More importantly, one must consider the loss of liquid levels in LPG receivers exposed to heat radiation must be considered—this can lead to a BLEVE.
If there is no heat radiation risk, it is advisable to empty the liquid LPG by pumping it to a safe destination after ensuring the closure of all pathways to the affected area.
The example shown in FIG. 2 shows that the pressure can be released to the flare header through a manual valve. In addition, after disconnecting the inlet to the amine scrubber, the pressure of the section from this column to the compressor can be released to the fuel gas header through a control valve.
Disconnecting fuel sources and releasing pressure by remote operation. In the control room and throughout the plant area, numerous means and devices allow operators to remotely perform critical disconnections of fuel and energy sources, and release pressure from the damaged sector.
Due to stress or confusion, an operations team may forget to use some of these measures, inadvertently extending the handling time of the event and potentially increasing the damage.
Some remotely operated devices are listed below:
It is advisable to prepare in advance dedicated screen displays in the control system for incidents of a fire or process materials release to make it easier for the board operators to perform what is required and (primarily) to ensure that no means at their disposal are overlooked.
Addressing and neutralizing nearby risks. Care must be taken during a fire incident in a process facility to deal with risks that might occur due to the fire and the heat radiation. Some common risk factors are listed below:
As part of the emergency response, it is essential to address the neighboring risks and alert the firefighting forces about them. In particular, it is crucial to apply cooling by firewater monitors for steel beams at risk of overheating, to operate deluge systems for LPG receivers, and to shut off the motors of air coolers.
Teaming up with firefighting and rescue forces. When firefighting and rescue forces arrive at the facility's premises in an emergency, crucial information must be transmitted quickly, including:
After their arrival, these firefighting and rescue forces should assume command of the firefighting and rescue activities. The operations team should focus on the operational activities for process shutdown (i.e., disconnecting the affected area from fuel and energy sources, releasing pressure, emptying liquids, and bringing the facility to a state as safe as possible).
Training and practice. In most cases, the providers of the initial response to an emergency at the facility will not be engineers or operations managers, but the field and control room operators on duty. These operators may spend most of their professional careers with only a few encounters with a severe emergency like a major fire incident. Therefore, without proper training and practice, the response of the operations team might be slow and incomprehensive, resulting in a longer-than-necessary response time and incident duration, increased damage and sometimes even harm to personnel.
Operations teams must practice the principles presented here to ensure that these principles are applied, even in moments of stress and excitement.
Plantwide exercises of emergency events usually concentrate on the functioning of the plant's systems and interfaces with external parties. Often, they do not deal specifically with the required practice of operational response. A suggested solution is to carry out orderly and structured emergency event exercises for the shift staff at least once a year per shift, in a manner that will be explained here. In addition, it is important to generate a constant dialogue on the subject and to carry out a "tactical practice" of various emergency scenarios during a conversation in an operators' room or control room. For example, a plant engineer would present a question to the operators, "The vacuum tower's bottom pump seal has failed, and a big fire started around the pump and under the pipe rack. How do you respond?"
It is important to end this discussion by presenting a formal solution consistent with the principles discussed here. Discussions on the handling of emergencies should be an integral part of an operations team’s everyday life so that in the decisive moment, the necessary actions are taken quickly and efficiently.
Exercises for dealing with an emergency scenario in refinery process units. The exercises proposed below aim to train the operations team in handling the hazardous material release or fire event by putting together exercise files based on a credible event of a release of process material accompanied by a fire or explosion. The files would hold all the materials required to provide an appropriate response following the principles presented in this article.
The proposed contents of an exercise file are:
Takeaways. The consequences of emergency incidents in oil refineries and petrochemical plants may be mitigated significantly if operations teams onsite act diligently to reduce the intensity of the fire or release of process fluids by using process tools, dealing with nearby risks, and interfacing effectively with firefighting and rescue forces.
Practicing fire scenario exercises on a regular basis will increase the chances of achieving the correct and efficient operational response from the operations team in the event of actual emergency incidents.
To obtain a timely response to emergency incidents, prepare dedicated screen displays on the plant's DCS that include all the available tools that can be used during emergencies and a convenient, straightforward means to activate them. HP
YARON NIMROD is a chemical engineer with more than 40 yr of experience in the oil refining and petrochemical industries. He has worked for the BAZAN Group of Haifa, Israel, as an Operations Manager, Projects Manager and VP for Technology and Projects. Nimrod is now teaching as part of the faculty of chemical engineering at the Technion in Haifa. He earned a BSc degree in chemical engineering from the Technion, Israel Institute of Technology, and an MBA from the University of Haifa.