CFESA Ventilation, Exhaust Hoods, and Kitchen Fire Suppression Systems — Questions and Answers
Question 1: What is the key functional difference between a Type I and a Type II commercial kitchen exhaust hood?
- Type I operates at higher static pressure than Type II
- Type I is designed to capture grease-laden vapors and requires a grease filter and fire suppression system; Type II handles only heat and moisture without grease (Correct answer)
- Type I is used only over solid-fuel equipment; Type II over gas equipment
- Type I requires makeup air; Type II does not
Correct answer: Type I is designed to capture grease-laden vapors and requires a grease filter and fire suppression system; Type II handles only heat and moisture without grease
Type I hoods are rated to capture grease-laden effluent and must incorporate listed grease filters and a fire suppression system. Type II hoods handle heat, steam, and odors from non-grease-producing equipment (dishwashers, ovens with no direct flame exposure) and do not require grease filters or suppression.
Question 2: A gas range fails to reignite after the kitchen's Ansul fire suppression system discharged. After confirming the gas valve is open, what is the most likely cause?
- The range's igniter module failed due to heat exposure during the fire
- The suppression system automatically shut off the gas via a fusible link or electrical interlock that has not been reset (Correct answer)
- The range pilot was blown out by the CO2 from the suppression agent
- The suppression dry chemical contaminated the burner orifices
Correct answer: The suppression system automatically shut off the gas via a fusible link or electrical interlock that has not been reset
NFPA 96 requires fire suppression systems to incorporate a gas shut-off — either a fusible-link mechanical valve or an electrical solenoid. After a discharge, these devices must be manually reset or the fusible link replaced before gas flow is restored. This is the most common post-discharge service call.
Question 3: What is 'makeup air' in the context of a commercial kitchen ventilation system, and why is it required?
- Filtered outdoor air introduced to replace the volume exhausted by the hood, preventing negative pressure that would impair hood capture velocity and equipment combustion air (Correct answer)
- The air recirculated inside the hood plenum to cool grease filters
- Pressurized air injected into gas burner ports to improve combustion efficiency
- Air supplied by the HVAC system to cool kitchen staff working near equipment
Correct answer: Filtered outdoor air introduced to replace the volume exhausted by the hood, preventing negative pressure that would impair hood capture velocity and equipment combustion air
For every cubic foot per minute exhausted by the hood, an equivalent volume must be supplied as makeup air. Without it, the kitchen develops negative pressure: exterior doors become hard to open, hood capture velocity drops, and atmospheric-combustion appliances can experience backdrafting and flame rollout.
Question 4: Under NFPA 96, how frequently must a commercial kitchen exhaust hood and duct system be inspected and cleaned at a minimum for a high-volume cooking operation such as a 24-hour restaurant with solid fuel or wok cooking?
- Annually
- Semi-annually
- Quarterly
- Monthly (Correct answer)
Correct answer: Monthly
NFPA 96 Table 11.4 specifies cleaning frequency based on cooking volume and fuel type. High-volume, solid-fuel, and wok cooking operations require monthly inspection and cleaning due to the accelerated grease accumulation that creates fire hazard.
Question 5: A technician notices that a deep fryer positioned near the edge of the exhaust hood capture area experiences frequent flame impingement and elevated flue temperatures. What is the FIRST corrective action to investigate?
- Increase the fryer's burner gas pressure to stabilize the flame
- Verify that the hood overhang dimension and exhaust CFM meet the equipment manufacturer's and NFPA 96 minimum capture velocity requirements for that appliance (Correct answer)
- Replace the fryer's thermostat, as high flue temp indicates control failure
- Clean the grease filters immediately, as blockage is redirecting heat
Correct answer: Verify that the hood overhang dimension and exhaust CFM meet the equipment manufacturer's and NFPA 96 minimum capture velocity requirements for that appliance
Flame instability and elevated temperatures near the hood edge indicate the hood is undersized or positioned incorrectly — insufficient overhang or inadequate CFM means the capture envelope does not fully contain the appliance's effluent plume. This is a code compliance and fire safety issue, not a fryer fault.
Question 6: What is the required maximum clearance between a listed grease filter and an open flame on cooking equipment below a Type I hood, per NFPA 96?
- 6 inches (152 mm)
- 18 inches (457 mm) (Correct answer)
- 24 inches (610 mm)
- 36 inches (914 mm)
Correct answer: 18 inches (457 mm)
NFPA 96 Section 4.2.1 specifies that grease filters must be installed at least 18 inches (457 mm) above cooking surfaces with open flames. This clearance is required to prevent grease filter ignition from direct flame contact.
CFESA Ventilation, Exhaust Hoods, and Kitchen Fire Suppression Systems
What is the key functional difference between a Type I and a Type II commercial kitchen exhaust hood?