As we have discussed in some of our recent articles, commercial kitchens have special requirements that must be considered by MEP design engineers. This also applies for fire suppression systems, since kitchens have more flammable substances and potential fire sources compared with most other commercial locations.
Before discussing fire suppression in commercial kitchens, it is important to understand that not all fires are equal. Since there are many types of flammable substances, the resulting fires also exhibit different properties. The fire classes in the USA are summarized in the following table:
FLAMMABLE/COMBUSTIBLE SUBSTANCE OR FIRE SOURCE
SUITABLE SUPPRESSION METHODS
Nonmetallic solids like wood, paper, and textiles.
The majority of suppression methods can be used.
Liquids and gases
Stop or inhibit the chemical chain reaction producing the fire. This is typically accomplished with dry-chemical fire suppression.
Fire suppression methods that do NOT use conductive substances like water.
Specialized suppression methods, specific for flammable metals
Cooking oils and fats
Oxygen supply removal or water mist.
Although cooking oils and fats are technically flammable liquids (Class B), they are in a class of their own (Class K) due to the special conditions found in commercial kitchens.
There are also European and Asian fire classification systems. There is some overlap between the classes among systems, but there are also important differences. When you see a fire class specification, make sure you also check the classification system being used.
Design a reliable fire suppression system for your kitchen.
Basic Principles of Commercial Kitchen Fire Suppression
Wet chemical fire suppression systems are normally used in commercial kitchens, and the UL 300 standard requires them for compliance. These suppression systems extinguish fires with the combination of oxygen depletion and water-based cooling:
The chemical agent includes an alkali substance, which forms a soap after reacting with fats - the process is called saponification. A foam layer forms above the burning oil or fat, interrupting the oxygen supply. Some common agents are potassium acetate, potassium carbonate and potassium citrate.
There is also a water content in the fire suppression agent, which cools oils and fats below their ignition temperature.
Kitchen fire suppression systems are connected to both equipment hoods and gas supply lines. Once the system activates, it interrupts the gas supply in addition to releasing the chemical agent; burning fats and oils are much more dangerous is gas is being released nearby. Equipment hoods are then used to remove the smoke resulting for fire suppression.
Commercial kitchen fires can quickly burn out of control unless effective fire suppression is present. Consider that kitchens are used in a various types of buildings with many occupants, including restaurants, hotels and event venues. In addition to being a mandatory safety measure, kitchen fire suppression provides a practical benefit: fires are normally extinguished quickly, before they can disrupt overall kitchen operations.
Which Standards Apply for Commercial Kitchen Fire Suppression?
In the USA, the main standards for fire suppression systems in commercial kitchens are the following:
UL 300: Standard for Fire Testing of Fire Extinguishing Systems for Protection of Commercial Cooking Equipment
NFPA 17A: Standard for Wet Chemical Extinguishing Systems
NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations
UL 300 Standard
The UL 300 standard was developed by Underwriters Laboratories in 1994, to establish suitable fire protection requirements for modern commercial kitchen equipment. The foodservice industry was evolving and cooking equipment was being modernized, so fire protection requirements had to be updated accordingly. Although commercial kitchens were becoming more efficient, they were also becoming more dangerous and fires had become more difficult to control.
The main requirement in the UL 300 standard is using wet chemical agents to suppress commercial kitchen fires. Other relevant requirements covered by UL 300 are the following:
Installing fire suppression nozzles in hoods and ducts, and over individual cooking equipment.
Installing a manual pull station to activate the fire alarm, located inside the kitchen area.
Automatic shut-off for the energy source in all appliances, electrical and gas-fired.
Fire suppression system inspection and servicing: Twice per year, by a licensed fire protection firm.
Hood and ductwork cleaning and maintenance: Twice per year, also by a licensed contractor. Baffle filters must be cleaned each week, or as recommended depending on the type of cooking.
NFPA Standards 17A and 96
The NFPA 17A standard applies for pre-engineered wet chemical fire extinguishing systems, throughout all project stages: design, installation, commissioning, operation, inspection, testing and maintenance. In general, the standard deals with wet chemical systems that use fixed nozzles and release the chemical agent with pressurized gas. The requirements provided are applicable to all wet chemical systems regardless of manufacturer differences, such as component design and the specific chemical agent used.
The NFPA 96 standard provides ventilation control requirements to complement the operation of fire suppression systems in commercial kitchens. The standard covers equipment such as exhaust hoods, ductwork, fans and air dampers. Commercial kitchen ventilation has special requirements due to the presence of cooking ingredient, grease and oil droplets in the air.
Commercial kitchen equipment provides efficiency in cooking operations, but it also comes with greater fire risks than a smaller residential kitchen. Fires from cooking oil and fat belong in a class of their own, due to the special requirements of commercial kitchens and the risk of rapid spreading.
Keep in mind that, where there is a commercial kitchen, there is also a crowd of people being served. Meeting safety and hygiene requirements is of utmost importance, and the best recommendation is working with qualified design professionals.
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