Besides producing flame, fire also produces smoke and heat. Hence to detect the existence of fire, heat detector can be used. Compared to flame detector and smoke detector, heat detector is slow in detecting fire because it only activates once a fire has produced sufficient heat of which heat detector could respond. However, heat detector could provide useful back up or as alternative to flame and smoke detectors. One mean to sense heat is by utilizing Fusible Loop System.
Fusible Loop System
The Fusible Loop System consists of the following:
Fusible plug which melt at set temperature
Tubing network
Fusible loop charge panel
During start-up, fusible loop is charged to allow air from instrument air system pressurizing the loop. The pressure remains constant during normal operation. If there is fire and the surrounding temperature rises, the fusible plug will melt.
The air in the loop relieves and subsequently the pressure inside the tubing reduces. Loss of pressure in the loop will be detected by pressure transmitter in the fusible loop charge panel and it will signal the control room. Next action in the control system could be activate fire alarm, trigger ESD, open deluge valve, etc.
Fusible Plug is non-resettable type. To restore the system into normal surveillance after activation will require replacement of parts i.e. the fusible plug.
The other disadvantage of fusible loop is that the plug could melt by other source of heat other than fire such as hot surfaces, motors, etc.
Hi, I would like to ask some questions regarding fusible loops.
For fusible loops that are being used around pumps that are being used to transfer hot process fluids/gas, how far would the plugs need to be installed?
Is there a standard or guideline that defines how far or close the plus have to be in respect to the motor that they are protecting?
Is it a requirement to use a fusible loops around pumps with hot surfaces/ process fluids or would a linear heat cable be suitable enough around such installation?
Fusible loops and linear heat cables are both used as safety devices in various industrial applications, including pumps. They serve to detect excessive heat or fire and actuate a fire protection system, either through melting (fusible loop) or by detecting heat changes along the cable (linear heat cable). However, the specific choice between these two options and the installation distance from the source of heat can depend on several factors, including:
Type of Process: The type of fluid being pumped, its temperature, and the potential for fire or explosion should all be considered when choosing and installing these devices.
Equipment Design: The specific design and layout of your pump, motor, and associated equipment will also affect these decisions.
Local and Industry Standards: Various jurisdictions and industries have specific standards and guidelines that dictate the use of these safety devices. In the US, for example, standards from the National Fire Protection Association (NFPA) often apply. You should consult the relevant standards in your jurisdiction or industry.
As for whether fusible loops are a requirement around pumps with hot surfaces/process fluids, this again can vary based on local regulations, industry standards, and specific operational contexts.
In some cases, a linear heat cable could be a suitable alternative or supplement, offering certain advantages such as being able to detect heat changes over a larger area. However, it’s important to consider all factors and potentially seek expert advice to make the right decision for your situation.