Commercial Cooking Fire Suppression Systems
Commercial cooking operations present an inherent fire risk. According to NFPA’s 2012 “Structure Fires in Eating and Drinking Establishments” fire departments in the U.S. responded to an annual average of 7,640 structure fires resulting in $246 million in property damage. Roughly 57% of those fires were caused by cooking equipment.
Clearly there is a need for reliable, efficient automatic fire suppression systems to suppress fires in cooking appliances, grease filters and exhaust ducts.
Beginning with adapted industrial dry chemical systems in the 1960’s, commercial cooking fire suppression systems have evolved to specially designed and tested wet chemical systems. These systems are tested mechanically and on live fires through various test agencies and test protocols including Underwriter’s Laboratories (UL) subjects and standards. Like the systems themselves, the test standards have evolved over the years as new cooking operations, methods, appliances, grease capture and grease vapor exhaust systems changed. As commercial cooking operations strived to maximize profitability and efficiency by using appliances that cooked faster through increased energy output, the fire risk increased dramatically.
In 1995, the commercial cooking world had to deal with the new test standard for fire suppression systems – ANSI/UL 300. Many changes took place regarding the suppression of fires in various appliances as a result of the new UL test standard. One of the things that didn’t change at the time was the fire detection for those systems. Every fire suppression system manufacturer continued to use fusible links, tied to a cable under tension, with a detector over every appliance and in the duct opening per NFPA 17A – Standard for Wet Chemical Fire Extinguishing Systems.
Since 1995, things have changed when it comes to detection for wet chemical systems. Fire suppression system manufacturers are looking at new ways of doing detection in an effort to pick up the fire faster, make the systems more reliable and make installation and maintenance of the systems easier. There are options regarding the type of cable that is used, different fusible links, different deployment of fusible links and a system that doesn’t use any fusible links. Let’s look at some of the options available today.
Link and Cable Detection
The most common or traditional detection system for wet chemical systems is still being used today. This consists of a stainless steel cable run through corner pulleys and conduit to detector brackets inside the hood behind the filters. Per the National Fire Protection Association 17A: Standard for Wet Chemical Extinguishing Systems, a detector and bracket connected with conduit and cable, is placed over each appliance and in the duct opening. The cable is placed under tension so that when the link separates, the release of tension fires the system and discharges the wet chemical onto the appliances, throughout the plenum and the exhaust duct. Proper placement of the detector in the path of the exhaust and proper temperature selection of the fusible link would lead to a faster response to fire.
This arrangement is still viable and used in a vast number of existing systems. Because grease can accumulate in the conduit to the point where the cable can become seized, it is essential that the conduit be cleaned or replaced on a periodic basis. Because they are constantly under tension or “load” and are subject to accumulating grease all systems using fusible links must have the links replaced every six months with fresh links.
Quick Response Links
Some manufacturers allow the use of “quick response” fusible links in an effort to detect and react to a fire faster. A faster detection and reaction time will provide better fire protection by minimizing the amount of damage sustained in a fire incident. The faster the fire can be detected, the faster it can be suppressed.
Alternate Detector Placement
Instead of placing a fusible link and bracket over each appliance and in the duct opening, some system manufacturer’s installation and design manuals are allowing the fusible links and brackets to be located on 24” centers throughout the hood length regardless of the placement of the appliances. This accomplishes effectively having detection throughout the entire hood, regardless of appliance placement or size. It also deals with the dilemma of adequate detection for large appliances such as large ranges or griddles. Because it still uses conduit and brackets it is still susceptible to grease accumulation and therefore should be cleaned or replaced periodically and the links replaced semi-annually.
Another new option that has emerged is the use of sheathed cable. Looking much like the cable used on bicycles, this cable is encased in a flexible sheath that eliminates the need for conduit and corner pulleys both outside and inside the hood. By using sheathing instead of conduit, the ability to accumulate grease between the sheathing and the cable is lessened. Because there is no conduit to measure and cut, the installation can be accomplished in less time and maintenance is also easier.
Carabineer / Lanyard Cable
This option consists of carabineers attached to lengths of stainless steel cable that is pre-measured and pre-cut and assembled at the factory. Carabineers clip on to the fusible links inside the hood on 24” centers or less. This eliminates the need to use brackets and conduit inside the hood, thus making cleaning of the lengths and replacement of the links easier. The maximum spacing of fusible links at 24” centers covers the entire hood and solves the dilemma of large appliances. Since the carabineer cannot fit through a corner pulley, this system is only available for use on either single hoods or hoods that are butted up end-to-end. It cannot be used for multiple, separate hoods, or hoods that are located back to back of each other. Since there is no conduit to measure, cut and fit, the installation tends to be faster and maintenance is easier.
This system does not use fusible links at all. Rather, a heat sensitive tube that is pressurized with air or nitrogen is run from a control device to the hood and then throughout the full length of the hood. When the tube is exposed to overheat or flame, it bursts, releasing the pressure and discharging the system. The entire length of tubing within the hazard area is a detection device. This allows for a faster response to a fire condition which could result in less damage from a fire. Unlike fusible links, the tubing must be replaced every three years instead of every six months. It does however, require cleaning every six months. Like the sheathed cable and the lanyard cable, there is no conduit to be measured, cut and fitted, so installation is faster and easier in some respects. Maintenance is easier as well. Without the conduit, there is no accumulation of grease that can cause the system to malfunction during a fire incident.
It can be assumed that commercial cooking fire suppression system manufacturers will continue to come up with new fire detection solutions for their systems. Look for innovations that will make the systems more reliable, easier to install and maintain while providing superior fire protection.
For further information, go to www.amerex-fire.com