Emergency Management and Response

Figure 1
Operating Limits

Once a process variable moves outside its normal operating range it enters the region of “trouble” (245-275 in the upper range in Figure 1). When a facility is in its normal operating range the system is controlled by its instrumentation; the operator usually does not have a lot to do except keep an eye on things. It is when things start to go awry , i.e., when the system runs into trouble that the skills of the experienced operators and maintenance technicians are called upon. As the system moves out of the trouble range (275 in the example) the system becomes increasing unsafe until eventually an emergency is declared (310 in the upper range of the example; there is no lower emergency limit in this case).

Levels of Emergency

An emergency response can be divided into three phases.  

1. The system is at or near the emergency limits, but the operators and supervisors believe that they are able to return the plant to normal conditions using normal operating procedures and techniques. It is critical that they understand the exact nature of the problem if they are to be successful in this. Many accidents would have been less severe had the operators not tried to “fight” the situation, but simply shut down the facility in an orderly manner. (On the other hand, a full facility shutdown is not always the best response to an incipient emergency because doing so increases the number of actions that the operator has to perform, and can stress many equipment items. The advantage of keeping the unit running is that the operators can concentrate on correcting the emergency situation. They do not have to simultaneously cope with bringing down all the other equipment in a safe manner. Moreover, the avoidance of a full shutdown means that the unit can be brought back on line relatively quickly with minimal production loss).
2. The second phase of an emergency occurs when the safety instrumented system and other high reliability, automated devices (including relief valves) take over. At this point in time the role of the operator is simply to secure the unit as it shuts down.
3. In the third phase of an emergency, the situation is out of control. There may be a large fire or chemical release to contend with. The full emergency response system is needed to minimize injuries, environmental damage and loss of equipment.

Figure 2 provides more detail to do with the third phase. It shows the ways in which emergencies can be initiated, along with the appropriate levels of response.

At the top of Figure 2 are the possible causes of an emergency: either an internal event such as the failure of a pump seal leading to a major fire, or an external event such as a lightning strike or an explosion at an adjacent facility. These initiating events can be identified, listed and analyzed when conducting hazards analyses and preparing a risk management plan. Factors to be considered when identifying potential accident scenarios include the location of a release, its magnitude, wind direction and the number of people who may be in the area at the time of the release.

It can be useful to model some of the scenarios, particularly the release of hazardous chemicals so that, if the accident actually does occur, the emergency responders will have some idea as to the size of the incident with which they may be expected to cope. Some companies even have on-line models that are available in real time. Then, if there is a release of that chemical, the response team can provide the modelers with current information so that a real-time prediction as to the magnitude of the incident can be developed.

It is important to identify any chemicals that require special treatment during the course of an emergency. For example, the use of water on some chemicals may cause them to ignite. In these cases, they must be controlled with other chemical agents.

A complicating factor is that most emergencies do not occur in isolation. Usually, there is a whole host of events going on at once. For example the immediate emergency may be hydrocarbon overflowing from a tank. However the cause of the overflow may have been the loss of electrical power to the site. That loss of power may also have compromised the fire-fighting capability of the emergency response team, or it may have led to a degradation of the internal communications channels. Moreover, if the spilled liquid were to ignite the subsequent fire could burn through a critical utility header. Environmental events, such as earthquakes, are particularly prone to creating multiple, simultaneous emergency situations. For example, the earthquake that causes lines and vessels to rupture may also break the fire water header, thus placing the emergency response team in a less than enviable position.

Emergency Operations

The first level of response can be termed “emergency operations”. A line operator or maintenance technician notices that an emergency situation is developing and quickly responds to bring the system to a safe condition. For example, if a pump seal fails and flammable hydrocarbon liquids are being sprayed into the air, the operator will usually shut down and block in the pump, hose down the area, get the spare pump started and call in maintenance to repair the failed seal. The emergency condition has been identified and corrected within just a few minutes.

If immediate operating response is not sufficient, the operator can shut down sections of the unit so that the affected equipment can be repaired. Procedures to do with emergency operations and shutdown tell the operator how to do this without causing any further damage and without jeopardizing other units. Once more, the facility remains in operation.

As a general rule, sources of heat such as fired heaters and steam reboilers should be shut down as an emergency develops. Cooling systems should continue to operate because they remove heat from the system. Utilities, such as the steam and air supplies, should remain in operation in order to retain control of the equipment that is still in operation.

If there is a major accident, an accurate head count will determine if anyone needs rescuing. Therefore, the facility managers must always know how many people are on the site at any one time. For larger facilities, they should also know roughly where those people are within the facility. If key-swipe cards are used, barriers can be placed between major operating sections so that a person’s location is always roughly known. The persons responsible for running the unit should always know how many people are on the site at any one time. For larger facilities, they should also know roughly where those people are within the facility.

Local Emergency Response

If an operator or maintenance technician recognizes that the situation is out of control and cannot be addressed through emergency operations, he or she can declare an emergency. With regard to the leaking pump seal the operator may not be able to get near the pump due to fumes in the area or because he feels that doing so would put him in danger. Therefore he calls in the facility’s own emergency response team. The personnel on this team will be trained in the handling of emergencies, and they will be issued with the appropriate equipment and protective clothing.

General Emergency Response

If the situation becomes too large for the emergency response team to handle then they can call for help from outside organizations, including the local fire department, ambulance services and other facilities in the area. The emergency plan must take into account the fact that these people are not familiar with the particular process where the emergency has occurred. Where possible, these outside agencies should have the opportunity of training with the plant emergency response team.