502.7.3.6 Fan motors and belts.
Electric motors driving exhaust fans shall not be placed inside booths or ducts. Fan rotating elements shall be nonferrous or nonsparking or the casing shall consist of, or be lined with, such material. Belts shall not enter the duct or booth unless the belt and pulley within the duct are tightly enclosed.Insight into this section:
This stipulation in the ventilation guidelines aims to minimize ignition risks by avoiding spark-producing components. It specifically forbids the placement of electric motors, which power exhaust fans, inside booths or ducts. This arrangement prevents the accumulation of overspray on the motor housing, which could lead to overheating. Additionally, the use of products prone to sparking is discouraged within spray areas. Belts driving exhaust fans must not be located within the spray areas due to their potential as ignition sources, unless the belts and pulleys are securely enclosed to protect them from solvents in the exhaust air that might degrade the materials and compromise the ventilation system.
Exhaust fans must be constructed from non-sparking materials, or at the very least, the fan housing should be made from such materials. This requirement is designed to prevent the fan from generating sparks when contacting its casing. It is important to clarify that the term "nonsparking" does not imply a complete absence of sparks. Components made from brass and similar materials can still produce sparks, but these have ignition energies too weak to ignite flammable vapors. However, these components must be meticulously designed to prevent the generation of frictional heat sufficient to cause ignition.