In part one of this article, we discussed how knowledge of the various types of detectors could aid in the preplanning process, stating that “Noting the presence or absence of detectors and sensors during preplanning sessions can give responders an idea of what they will face in the event of a fire, explosion, leak or other incident”. In part two, we will discuss sensors other than the more typical detectors used in fire protection. We will also discuss why when detectors and sensors are not provided where needed incidents may be more frequent and more severe.
Examples of sensors that will provide insight into what responders can expect and what is expected of responders:
• Low Liquid level interlocks in electroplating tanks are intended to prevent the heating element from igniting the plastic (or plastic lined) tanks and associated plastic ductwork.
• Hi and Hi-Hi alarms on storage tanks are intended to prevent liquid overflow from a tank.
• Conveyor alignment and bearing overheat sensors are intended to prevent friction from igniting combustible conveyor belts or the materials they are conveying.
• Gas train high and low pressure gas switches are intended to prevent a flameout and unburned gas from filling a boiler or oven. Once a hot surface is found, a gas explosion could ensue.
• Cooling water incursion into any kind of molten material such as steel, aluminum, glass, or paper liquor smelt can cause a major explosion. Extensive and reliable water leak detection is essential.
• Insurance company guidelines recommend numerous sensors for thermal oil systems so that oil heated above its flashpoint does not leak or feed a fire.
Sometimes a facility and the fire service need to know about a problem but do not want any automatic action taken. An example is low oil pressure on a diesel fire pump. The responders need to know about the low oil pressure but do not want that problem to shut down the engine. Fire pumps are expected to run to destruction during a fire . When process pumps are substituted for fire pumps, they may come with shutdowns that are intended to protect the pump or motor. This is not desirable for fire situations. Fire pump monitoring expectations are found in National Fire Protection Association (NFPA) 20, Stationary Fire Pumps.
The wide variety of examples given above represents only some of the uses of sensors that the fire service usually does not learn about at the fire academy. Knowing what detection and what sensors are present (or absent), gives a better idea of what you might face.
What to Expect When Needed Detectors/Sensors Are Not Present:
Essentially, the responder can expect more frequent and more severe incidents. For example, if a conveyor does not have alignment limit devices or roller bearing thermocouples; then conveyor fires will probably be more frequent. If a high value electronics room does not have some type of very early warning smoke detection system, then the fire, once discovered will be larger (with potentially very acrid smoke generation) and could cause more damage and business interruption.
Sensors and interlocks should be checked to be sure they are not bypassed. Often, if these devices cause a process to trip off line, a technician will bypass them rather than looking into the cause. A bypassed sensor is worse than no sensor because it implies a level of protection that does not exist. It also reflects negatively on overall facility management.
Asking about what types of sensors are present can give you valuable insight on what the facility is trying to prevent. Because sensors can fail, the fire service will have an idea of what to plan for. By knowing what kind of sensors should be provided but are not (which are published in insurance company guidelines) the fire service can expect more frequent and more severe incidents.
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