The W Rating was introduced to the ANSI/UL1479 firestop standard in 2004. It measures the ability of a firestop system to provide watertightness. Before the fire and hose stream tests, the firestop system is immersed in water and subjected to 3 feet of water column for 72 hours. The test is successful if no leakage occurs, and the firestop system passes the fire and hose stream test for the specified period.
The W Rating was developed to address situations where a flooding event could happen inside a building. Examples include burst pipes or even accidental sprinkler discharge. It is important to note that while many firestop products are water-resistant, the expectation is that the water exposure is transient, such as a spill or scrub water from floor cleaning, and not a more significant flooding event. Accordingly, the products typically used to achieve W ratings are silicone sealants or devices that include gaskets. Latex sealants, while water-resistant, may not provide water tightness as water can eventually weep into the bond line and cause the seal to fail.
Since silicone and rubber gaskets are inherently more water-resistant, they also provide a measure of washout resistance. These products can be great for unenclosed buildings under construction. Washout resistance has almost become synonymous with the W Rating, even though it has nothing to do with the test. For that reason, sometimes people look for W Rated systems in places like South Florida or Seattle, where there may be frequent rainfall. People say they do not need W Ratings in more arid areas, like Arizona or Nevada.
No matter what, a building owner can benefit from a firestop system with a W Rating. Whether the building is in a wetter or drier environment, a burst pipe can happen anywhere. If undiscovered or the main water supply cannot be shut off quickly enough, flood damage to the building can be significant and costly to remediate. For the nominal difference in product cost, W-rated firestop systems provide peace of mind.
This article, by James Stahl Jr., VP & General Manager, Engineering & Emerging Businesses, originally appeared in the Winter Wrap 2024 edition of The Burn.