Why do Grease Ducts Require Fire Protection?
Leading Causes of Structure Fires in Eating and Drinking Establishments by Major Cause: 2006-2010 (Top 5 Shown).
Source: U.S. STRUCTURE FIRES IN EATING AND DRINKING ESTABLISHMENTS, Ben Evarts, National Fire Protection Association, Quincy, MA, November 2010. http://www.nfpa.org/assets/files/PDF/EatingExecSum.pdf
Fire Event – Grease Duct
Wynn Casino, Las Vegas, NV
Clark County fire officials credited a mechanical system at Wynn Las Vegas for preventing the spread of a fire in a grease duct this morning. Officials evacuated people located near the restaurant and in the sports book while they extinguished the small fire, Welling said. An engineer employee was examined for smoke inhalation, she said. No one else was injured. Fire crews also closed several northbound lanes of Las Vegas Boulevard to access the hotel property, Welling said.
Update: Stratta is open for business, although the restaurant’s pizza oven is temporarily out of commission as a result of the fire, officials said. (“Firefighters Called to Small Blaze”, Las Vegas Sun October 9, 2011)
Grease Duct Testing Code Requirements
Engineering standards exists to help provide guidelines on the proper methods to provide the required protection. The international Mechanical Code (IMC), Uniform Mechanical Code, and NFPA 96 are mirror one another on providing effective way for grease duct enclosure. These standards require to provide a protection on grease ducts that penetrates a rated assembly in accordance with ASTM E 814/UL 1479 and having a F & T rating equal to the fire-resistance rating of the assembly being penetrated. Also, providing a proper duct enclosure has been an approved method since 2006. These standards mandate a field applied grease duct enclosure to be tested to ASTM E2336 (Standard Test Methods for Fire Resistive Grease Duct Enclosure Systems).
The International Mechanical Code -Section 506, 2006 Ed. states that a grease duct which is serving a Type I hood that penetrates a ceiling, wall, floor or any concealed spaces shall be enclosed from the point of penetration to the outlet terminal. A clearance should be maintained to the interior surface of enclosures of combustible construction shall be not less than 18 inches (457 mm) and noncombustible construction or gypsum wall board attached to noncombustible structures shall be not less than 6 inches (152 mm).
NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations, 2014 Ed. states in section 4.2.1 where enclosures are not required, hoods, grease removal devices, exhaust fans, and ducts shall have a clearance of at least 457mm (18 in.) to combustible material, 76mm (3 in.) to limited-combustible material, and 0mm (0 in.) to noncombustible material. In section 184.108.40.206, describes that Zero clearance to limited-combustible materials shall be permitted where protected by metal lath and plaster, ceramic tile, quarry tile, other noncombustible materials or assembly of noncombustible materials, or materials and products that are listed for the purpose of reducing clearance.
Confirming that clearance to combustibles is met the day a building opens is reasonable, but ensuring this is maintained over the life of a building poses a serious challenge. Providing a zero-clearance enclosure along the entire duct run affords added safety and peace-of-mind.
ASTM E 2336 Test Summary
Section 16 of ASTM E 2336-04 contains five “Conditions of Compliance”, which are described below along with a synopsis of the passage criteria:
16.1 Non-combustibility (ASTM E 136) Immersion of samples into 750°C vertical tube furnace.
<30s flaming and <30°C heat rise.
16.2 Fire Resistance Test (ASTM E 119) Vertical wall panel test. Cold side average <250°F above initial, individual <325°F above initial, no passage of water through wall panel during hose stream test.
16.3 Durability (ASTM C 518) ten cycles of material at 300°F for 12 hours then ambient for 12 hours. After the temperature cycling, the increase in average thermal conductivity of the material must be less than 10%.
16.4 Internal Fire Test 500°F duct soak for four hours, then ramp up to 2000°F for 30 minutes. Unexposed (non-fire side) surface average <250°F above initial, individual <325°F above initial.
16.5 Fire Engulfment (ASTM E 119), through-penetration must pass ASTM E 814 through-penetration firestop requirements. Supports and enclosure integrity must remain intact without a through opening during fire and subsequent hose steam.
3M™ Fire Barrier Solution for Grease Ducts
3M™ Fire Barrier Duct Wrap 615+ provides excellent insulating capabilities and offers a space-saving alternative to traditional bulky fire protection methods such as installing a gypsum wall shaft or enclosure. This wrap is commonly used in commercial kitchen grease ducts, as well as ventilation air ducts. Duct Wrap 615+ protects both air and grease ducts for up to two hours. 3M™ Fire Barrier Duct Wrap 615+ is an ideal fire resistive enclosure for commercial kitchen grease ducts and ventilation air ducts. It is a proven performance alternative to a 1- or 2-hour fire-resistant rated shaft enclosures for grease ducts and provides zero clearance to combustible construction throughout the entire enclosure system.
Using Gypsum Shaft method is a space consuming. For example, 18-inch duct consumes about 22.5 square feet of space. On the other hand, using 3M Duct Wrap 615+ consumes about 4 square feet of space — almost 80% less!
Author: Assaf Aweisi, Senior Application Engineer at 3M EMEA.
Author Background: Bachelor of Science in Industrial Engineering, NEBOSH Certified – International General Certificate in Health and Safety, CFPS (NFPA) Certified – Certified Fire Protection Specialist.