Smoke Vent Labeling Comparison: UL 793 vs FM 4430

Smoke Vents are often times specified on buildings, as required by International Building Code, to help evacuate smoke, heat and toxic gas from a burning building. Often, one of the requirements is either UL or FM testing and labeling.

UL 793 is by far and wide the most common testing and labeling requirement, but occasionally FM 4430 is a requirement. Although these standards are similar, FM may be a requirement when the building is insured by Factory Mutual. Below is a table comparing UL 793 to FM 4430.

UL 793 FM 4430
Cycle Test – Open and Close 250 60
Automatic Opening
UL33 listed heat responsive device or fusible link in range 160°F – 520°F Minimum 360°F rated heat sensing device so not to activate before sprinklers
Operation Operates manually from the inside/outside of the building Operates with manual opening device from floor level, additional permitted
Snow Load Opens against 10psf Opens against 10psf in max 10 seconds
Wind Uplift 30, 60 or 90psf 60psf minimum; test to failure
Impact Resistance 100 lbs at 4 ft 100 lbs at 4 ft
Fire Resistance Testing Class A UL 790 fire-rating for aluminum

HB flammability per UL 94 for domes

Fire exposure test for domes

The main difference is that UL requires fusible links in the range of 160°F – 520°F. Additionally, FM recommends that the vents do not open before the sprinklers so FM typically calls out the fusible links 100°F higher than the sprinkler link.

Nystrom understands the codes and complexities of Smoke Vents. To learn how Nystrom can assist on your next project, please visit