Black Box Explains...Firestop Basics
Cables pose a fire risk.
Most cables are constructed with standard polymer jackets, which are combustible. Copper and aluminum are the most common metals used as conductors. Unfortunately, they’re good conductors of heat. The conductors can spread a fire by igniting surrounding flammable materials, such as the cable jacket. Then the jacket burns away, the conductors melt together, and the size of the cable bundle shrinks and causes gaps to develop within the cabling opening.
Successful firestop planning.
A well-designed cabling system requires careful planning to meet the needs of future cabling requirements and fire protection. Most people tend to underestimate the size of the openings required for cabling and often forget about future expansion. When planning on how large to make the opening to run your cable, you must consider the diameter of the cable itself, how much room you need for firestopping materials, and whether you’ll be adding more cables in the future.
Permanent vs. retrofittable cabling.
There are two basic types of cabling systems: permanent and retrofittable. Permanent cabling systems, such as electrical cables, do not change. But most cabling systems, such as data and voice, have to accommodate moves, adds, and changes so they need to be retrofittable. You use different firestops with each system.
In permanent installations, a sealant is used in and around the cables. This is also appropriate for external areas, including conduits and sleeves.
In retrofittable systems, firestops need to be removed and reinstalled easily as cable needs change. Common firestops include pillows, putty, and fire-rated pathways. These products are packed in and around a cable bundle rather than being injected the way sealant is. The product to use often depends on the size of the cable opening and the frequency of changes.
Passive vs. intumescent firestopping.
There are two basic types of materials used in firestopping: Passive firestopping uses nonintumescent materials, which draw heat away or insulate the cables. Passive materials include mortars, silicone sealants, foam, and grout. Cabling runs with passive firestopping are generally thicker and are more limited in the types of cables they can protect.
Intumescent materials expand when exposed to heat or fire and compensate for the loss of mass in cable bundles. They’re a good choice for sealing and surrounding cable holes and runs.