From Industrial Fire Journal - Fire & Rescue - Hemming Group Ltd and www.HemmingFire.com
Fire detection: challenges and solutions
Published: 28 May, 2014
Fire alarm control panels and accessories have improved dramatically in design, reliability, flexibility and price. The vast majority of systems supplied throughout the world are installed in the residential and commercial markets. Therefore, the panels and accessories are tailored to those markets, locations such as hospitals,schools, and office buildings. When systems are designed for the
industrial market, numerous environmental challenges are encountered that are not present in residential or commercial markets. A brief discussion of those challenges and solutions follow.
Standard enclosures must balance aesthetics with accessibility. They are typically rated NEMA 1/IP 10, which is well suited for an office complex but is totally inappropriate for a metals processing facility. Some manufacturers offer enclosures rated to withstand industrial environments but the vast majority leave that up to the designer/installer. When choosing an enclosure it is therefore important to consider the following:
1. Area Classification: Does the possibilityof explosive vapours or dusts exist? If so, the enclosure may require pressurization or an explosive rating.
2. Temperature: Will temperature conditioning be required to either heat or cool the electronics mounted within the enclosure? Check the manufacturers’ data sheets to ensure the expected
temperature does not exceed its recommended operating parameters.
3. Venting: Most batteries require free air venting to avoid the possibility of gas build up while they are being charged.
4. Material of Construction: Weather resistant enclosures fabricated from mild steel coated with protective paint finish may be the best choice to preclude ingress of dust and moisture but if the unit is placed in a corrosive environment close to a body of water or in a facility such as a water treatment or sewage plant, more corrosion resistant materials such as stainless steel or fiberglass may be the most logical choice.
5. Access: While it is important to house the panel properly, accessibility to respond to an alarm, acknowledge trouble or fault conditions, reset or silence an alarm condition must be maintained. Window kits which maintain the integrity of the panel can serve to ensure compliance with this aspect of the design. Ingress protected switches can be mounted to the enclosure or in a separate
junction box located adjacent to the enclosure.
Main feed to the control panel in an industrial setting may be problematic. The quality of power may not be to the levels anticipated by the fire alarm control panel manufacturer. Unanticipated voltage dips may be experienced when large motors are energized. Frequencies generated by electronic motor controllers have caused trouble conditions. Where multiple buildings are protected, the potential
difference in the ground plane may create problems for ground fault circuitry.
Some of these situations can be avoided by adding isolation transformers to the incoming power feed. Ground faults can be reduced by checking the ground potential when different buildings are added to the control panel. Surge suppressors can help reduce the destructive potential of lightning strikes and other unplanned environmental conditions.
Connection Between Structures
Most modern control panels allow the communications link or SLC loop to be installed utilizing copper conductors or fiber optic cable. Connections between buildings (especially those elevated in open air) are prone to damage by adverse environmental conditions especially from lightning strikes. Surge suppressors help minimize damage. Fiber optic cable may offer an alternative to copper and reduce the likelihood of damage to the communication loop.
In most cases the flexibility of addressable control panels makes them the logical choice for use in the industrial sector. Programming features are very robust and tractable and addressable panels have the capability to pinpoint the location of a device in trouble or alarm. In the industrial sector clients are typically very familiar with Programmable Logic Controllers (PLC) and may not understand the limitations of Fire Alarm panels and ask why they are not as flexible as the PLC’s used to operate their plants. Fire alarm control panels are designed and configured to meet operating parameters established by international approving authorities, fire officials, code making bodies and local governmental agencies. The environment in which the main controller is installed may be reasonably
controlled; locating field modules and associated devices can be more problematic.
Typically when discussing devices associated with addressable control panels we immediately think of smoke or heat detectors. All manufacturers also offer modules to address dry contact and current
limiting devices such as flow, tamper and pressure switches, conventional heat detectors, call points, etc. As devices are deployed throughout the facility it is of utmost importance to ensure that those devices are installed within their environmental range.
The temperature range of addressable modules must be considered during design and installation. Each manufacturer publishes the temperature range for their devices; if they are installed in areas that exceed those parameters, the device may fail prematurely or cause sporadic trouble conditions.
Installing these devices near ovens, furnaces, or where they may be impinged upon in a fire condition may result in temperatures exceeding the design parameters of the device, causing potential problems. A better choice would be to locate them in a conditioned space as close to the device being monitored as possible.
Alarm and Signaling
Industrial facilities can run the gamut from high tech streamlined manufacturers of automotive or aerospace products to foundries. All have many similarities: the processing areas are noisy and usually have quite a bit of traffic moving through crowded aisles ranging from fork lifts to automatic guided vehicles. Emergency override switches are strategically placed and flashing indicator lights are the norm. This makes selection and placement of call points and signaling devices a challenge. Typically, placement of these devices is mandated by local codes and standards. Thought must be given to the style, type and location of call points and signaling devices. They must be both accessible and easily identifiable in an emergency situation. They must give clear notice of a fire condition along with indicating a path of safe egress.
Not only must the device be more durable in an industrial setting, it also must meet any electrical or flammability ratings for the area in which it is installed. Explosive atmospheres require unique devices that normally require much more power than a standard audible-visual indicator. Strobe candela and horn decibel ratings most likely will have to be at the high end of the available range. In
certain areas additional devices or high output units must be used. This increases the load on power supplies and associated battery backup.
Wire size will need to be increased to support higher current requirements. All of this adds to the cost and complexity of the installation.
Selection of detection devices can be quite a challenge in an industrial setting. The vast majority of systems designed for the commercial setting rely on smoke and heat. When working in industrial
occupancies it most likely will be necessary to expand our knowledge base to a wider array of device and sensor technologies. A very brief synopsis of some widely used devices follows:
1. Linear heat detectors are widely used to protect cable trays, conveyors, and rack storage to name but a few suitable locations.
2. Air aspirated smoke detection technology has advanced beyond the traditional clean high air flow environments to protect hazards once thought to be environmentally unacceptable for such early
warning technology. Fitted with appropriate filters, the current generation of air sampling detectors has the capability to discriminate between particulate matter generated by the combustion process and
larger particle dusts which can be a by-product of many industrial processes. One manufacturer has added gas detection capabilities to their detector sampling networks allowing one sampling network to perform multiple functions.
3. Fixed gas detection is used in process facilities, tank farms, truck and rail car loading racks, and numerous other locations.
Normally wiring methods and devices in these facilities are electrically rated as flammable or explosion proof. Current technology relies upon infrared or catalytic bead sensors interconnected to or integrated with transmitters using relay contacts or 4-20 MA outputs. Sensor choice and
location are key to ensuring reliability and improving sensor life.
4. Flame detection offers rapid response to open burning from the smallest to large fires. Specialized detectors are used where hard to see fuels like hydrogen flames and non-carbon based materials are
processed or stored. Detectors are offered in traditional ultraviolet and infrared spectrum as well as multi-spectrum devices to target specific materials. Video fire detection offers the added benefit of
being able to stream video of the protected area.
Fire extinguishing and suppression systems must be considered in the design and supply of the Fire Alarm system. Monitoring of traditional fire sprinklers does not present major challenges to most
control panel designs, but nuances associated with Clean Agent, CO2, Foam, Dry Chemical, Explosion Suppression and other systems encountered in the industrial sector may be a challenge to the panel designer and may be best addressed utilizing control panels specifically configured for that application. Normally volt free contacts are available to indicate trouble and alarm conditions and should be interfaced with the system.
Industrial applications present unique challenges for fire alarm control panels, but the technologies to address these challenges are available.
The right combination of panel and accessories exists. It is only necessary to understand the nature of these challenges by considering each concern as outlined above in order to find the solution that fits
the specific environmental, logistical and price constraints imposed by the individual application. Working with the right supplier who will take all these factors into consideration will make a potentially complex process both straightforward and successful.