Smoke Extraction of the Kitchen Exhaust Hood and Current Regulations

In this article, we will discuss the requirements of the CTE DB SI Fire Safety Regulations for the smoke extraction of kitchens in our buildings. First, the regulations classify spaces into three types according to risk, classifying kitchens by their installed power. Between 20 and 30 Kw, they will be considered low-risk spaces; between 20 and 50 Kw, medium risk; and more than 50 Kw, high risk.

To determine the installed power, the Code only considers the appliances intended for food preparation that may cause combustion. Thus, frying appliances (such as fryers and tilting pans) will be calculated with an intensity of 1 Kw per liter, regardless of their power.

Requirements for the smoke extraction of exhaust hoods

Regarding the smoke extraction of exhaust hoods, if these are located in spaces considered to have special risk according to the aforementioned, they must comply with the following special requirements:

Location

Exhaust hoods must be located at a minimum distance of 50 cm from any material classified as A1. (A1 material: non-combustible material that does not contribute to the maximum propagation of fire).

Extraction ducts

The extraction ducts for smoke and cooking vapors must not be connected to other extraction ducts, but must be independent and exclusive for this specific ventilation. It is mandatory to include inspection openings for proper evaluation and hygiene in elbows with angles exceeding 30°. Also, every 3 meters in horizontal sections. Ducts located inside the building or located on a facade at a distance of less than one and a half meters from areas that are not at least EI 30, or balconies, terraces, or operable openings, must have an EI 30 classification.

Fire dampers

Fire dampers should not be installed in these extraction ducts.

Filters

If the heat source is from a gas kitchen, the filter must be at a minimum distance of 1.20 meters. In other cases, the minimum distance can be reduced to 0.50 meters. The inclination of the filters must be greater than 45° and must be removable for replacement and cleaning.

UNE-EN 12101-3

Extractors must comply with the requirements of the UNE-EN 12101-3 standard "Specifications for Mechanical Smoke and Heat Exhaust Ventilators" and have a classification of F400 90 (i.e., they must guarantee their operation at 400 °C for 90 minutes).

In any case, for kitchens installed in hospital or public residential facilities (see usage description according to CTE DB SI) where the installed power exceeds 20 Kw and in kitchens with a power of 50 Kw in buildings of any other use, an automatic extinguishing device must be available.

Aspects to consider

To ensure proper smoke extraction from exhaust hoods, various aspects must be considered:

• The free suction area of the exhaust hood.

• The number of open sides of this exhaust hood.

• The total power (Kw) of the electrical appliances in the kitchen area.

• The location of the extractor.

• The passage area of the ducting for this specific kitchen ventilation.

• According to the design of the installation and the location of the exhaust hood, the load losses will be calculated. To avoid problems with noise and vibrations, the air velocity in the duct must exceed 10 m/s.