Today’s commercial buildings are constructed with fire-rated separations to contain the spread of flame and smoke. The critical juncture for plumbers is when fire separations are penetrated with piping systems.
For combustible materials like plastic, these penetrations must be sealed, at significant expense, to the original fire integrity of the compartment with a fire stopping system tested by a nationally recognized lab to ASTM E-84 or UL 723 Smoke and Flame Spread test.
Being a thermoplastic, plastic piping will combust and lose its structural integrity at low temps, leaving an opening that will allow the spread of smoke and flame. To counter this, fire stop materials are required to seal these penetrations.
Installed in the annular space, these materials expand when exposed to high heat. A common fire stopping assembly for plastic piping through concrete floors consists of a ring of intumescent material held in place around the pipe with a metal collar.
This assembly involves shooting masonry anchors into the concrete, clamping the collar in place and installing a smoke seal with a bead of fire resistant caulking.
The expected service life of these intumescent materials vary significantly by manufacturer. Some fire stop manufacturers claim service life measured in decades, some make no claims of an expected service life.
Although a test method for aging of intumescent materials has been developed, there is no established method for using the results to calculate service life. As with any potentially life-saving product, these fire stopping materials must be installed properly, tested and listed by an accredited third-party agency before use.
Un-ducted return air plenum areas are also critical. Model codes are very restrictive regarding the use of combustible materials in plenum areas. Plastic pipe tested to the ASTM E 84 test protocol and achieving values equal to or less than 25 (flame spread) / 50 (smoke developed) is generally considered the minimum for inclusion of a combustible material in a plenum area.
It is important to note that neither PVC nor ABS meet the 25/50 rating.
Cast iron piping will not melt or burn away in a fire, meaning designers and
engineers can avoid the added cost and complexity of adding fire stopping materials to their piping assemblies for every penetration in a building.
All that is required to seal a cast iron penetration is some mineral wool batting and fire-resistant caulking around the pipe. Simpler, faster and much more cost effective. And the more floors in the building, the greater the cost savings.