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September 2005: Cafeteria Extinguishing Systems

It is common to find pre-engineered extinguishing systems in commercial cafeterias. These systems serve to suppress grease and oil fires in fryers, grills, hoods, and exhaust plenums. In the past dry chemical extinguishing agents were adopted for pre-engineered local application kitchen extinguishing systems because of issues about dumping water on burning oil or grease. Dry agent extinguishing systems have also been reliable and cost-effective systems to install. However, changes in cooking oils and cooking equipment have resulted in changes for these pre-engineered extinguishing systems.

While these changes were first reflected by UL and NFPA in the mid-1990's, many state and local jurisdictions have granted time frames to phase out dry chemical systems for commercial cooking operations. It would be prudent to be aware of the type of special extinguishing systems installed in your cafeteria facilities, because phase out times required by local jurisdictions for system replacement may be approaching. Additionally, the company servicing your extinguishing equipment may no longer be replacing parts or offering inspection services for older systems. But most important of all, the extinguishing systems in your cafeteria kitchen protecting the fryers may be providing a false sense of security. The following is a brief summary of changes that have taken place.

The switch from animal-fat based frying and cooking oils to vegetable-based oils has resulted in higher cooking temperatures. There have also been significant improvements in the cooking equipment itself in terms of quicker heating times and improved insulation. These equipment improvements not only increase efficiency, but also increase cooking oil cooling times when power or fuel to the equipment is shut off. While auto-ignition temperature of most animal-fat based cooking oils is between 550°- 600°F, auto-ignition temperature of vegetable oils is 685°F or higher.

This combination results in high challenge fires with a high potential for reflash in circumstances where traditional dry chemical extinguishing agents fail to suppress the flame.

Testing also demonstrates that the temperature required for reflash decreases with the age of the cooking oil. This means vegetable based cooking oils, once ignited, will continue to re-ignite at lower temperatures the longer the oil is in use; unless an extinguishing agent can reduce the oil temperature below the oil's declining reflash point.

Due to these factors, it has been verified through testing at Underwriters Laboratories that traditional dry chemical extinguishing systems cannot extinguish fires involving vegetable-based cooking oils. Dry chemical extinguishing agents include a family of chemicals; such as, mono ammonium phosphate, sodium bicarbonate, and potassium bicarbonate. To a lesser degree, potassium chloride and potassium sulfate may also be used in dry chemical extinguishing applications.

Mono ammonium phosphate is commonly known for its use in ABC Multi-Purpose extinguishers covering Class A fires (ordinary combustibles); Class B fires (flammable liquids), and Class C fires (electrical). It is also considered messy and corrosive. Both sodium bicarbonate and potassium bicarbonate are commonly used for Class B and C fires. In the past, all three extinguishing agents were permitted for special extinguishing applications for commercial cooking equipment.

The problem that cropped up with vegetable based cooking oils is that these agents do not provide any properties for cooling the oil below the reflash point. This had not been a major issue with animal-based cooking oils. The family of dry chemical agents extinguishes fires through a process known as "saponification." What happens in saponification is the agent reacts with the burning material's surface and creates a thin foam barrier, or "blanket", across the burning surface that eliminates oxygen - and presto!, no more fire. However, it has been demonstrated that vegetable oil fires need extinguishing agents that cool, as well as provide saponification.

As a result, Underwriters Laboratory, in conjunction with extinguishing industry leaders, developed UL 300, Standard for Safety for Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas. This standard was created and adopted side-by-side with changes made by NFPA in Standard 17 (Standard for Dry Chemical Extinguishing Systems), Standard 17A (Standard for Wet Chemical Extinguishing Systems), and Standard 10 (Standard for Portable Fire Extinguishers). It should be noted that dry chemical extinguishing systems are still permitted by NFPA 96 (Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations, 2001 Edition) to protect hoods and plenums. Otherwise, UL no longer lists pre-engineered dry chemical systems for commercial cooking equipment.

This is also a new class of extinguishing agents that came into play for commercial cooking equipment. Class K extinguishing standards for wet extinguishing chemical agents were developed and adopted by NFPA and UL to reflect the category for commercial cooking equipment. The wet extinguishing chemical agents provide both cooling and create a thin foam blanket to eliminate oxygen. This family of agents includes potassium carbonate and potassium acetate mixed with 40% - 60% water by weight, depending on the manufacturer. These are not perfect extinguishing agents by any stretch of the imagination. But their performance is far superior in effectiveness because they cool the cooking oils.

Because their performance is not perfect, portable fire extinguishers are vital to the overall extinguishing protection plan for deep fat fryers, tilting skillets, and braising pots. The fact that saponification is a process of creating a "soapy" foam condition rightfully suggests that acidic compounds hinder the process. For this reason, the use of ABC Multi-Purpose extinguishers (mono ammonium phosphate) will do more harm than good by attacking the foam layer. This type of extinguisher, or extinguishers with potassium chloride or potassium sulfate agents, should not be allowed near commercial cooking equipment.

It is important to have portable Class K (wet chemical) fire extinguishers to complement pre-engineered wet chemical extinguishing systems. Equally important is a good training program in which kitchen employees gain actual user experience in the proper use of hand extinguishers. Moreover, many commercial kitchens today employ people from a number of bi-lingual nationalities, so it would also be prudent to provide bi-lingual placards for emergency equipment.

How to tell if a pre-engineered extinguishing system in a commercial kitchen meets UL 300 and NFPA 17A standards:

• Be sure to inspect the equipment for the UL300 label on extinguishing tanks for the systems.

• You may also cross-check the model number with the UL listing directory.

• The extinguishing system service company should also be able to determine if the system is a listed wet chemical extinguishing system.

• Ask an expert the service company that regularly services the equipment should be able to verify compliance.

• In all cases systems installed prior to 1994 should be checked.

Three things to be aware of:

• The majority of extinguisher system manufacturers have established dates after which point they will no longer provide parts for older systems, or recharge them.

• Some state and local jurisdictions have mandated compliance with UL 300.

• Current NFPA standards require a UL 300 compliant system if the existing system has been expanded or moved.

Planning for these changes can help reduce the cost of becoming compliant, and more importantly, provide the level pf protection you need.

References:

National Fire Protection Association, NFPA 10, Standard for Portable Fire Extinguishers, 2002 Edition.

National Fire Protection Association, NFPA 17, Standard for Dry Chemical Extinguishing Systems, 2002 Edition.

National Fire Protection Association, NFPA 17A, Standard for Wet Chemical Extinguishing Systems, 2002 Edition.

National Fire Protection Association, NFPA 96, Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations, 2001 Edition.

Rolf Jenson Associates: "Fire Extinguisher Roundup" Issue 14 - International Fire Protection Magazine, May 8, 2003, pp 41-46.

Underwriters Laboratories Inc., UL Standard for Safety for Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas, UL 300, Second Edition, March 29, 1996.

Underwriters Laboratories Inc., UL Standard for Safety for Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas, UL 300, Second Edition, March 29, 1996.

Underwriters Laboratories Inc., UL Standard for Pre-Engineered Dry Chemical Extinguishing System Units, UL 1254, Second Edition, June 28, 1996.