UL-ULC Smoke Alarm Standard Harmonization
Scott Lang Senior Engineering Manager – Industry Affairs, Honeywell International
The Canadian and US product safety standards for smoke alarms are harmonized as of the 5th edition of ULC 531-2024, which was published in November 2024. Like the smoke detector standards, it has taken more than 20 years of effort by US and Canadian technical committees to reach this milestone. As was mentioned in my previous CFAA article in the December 2023 edition of the Journal, harmonization of product requirements has benefits for all stakeholders involved with product certification and standardization, including the public. ULC 531 now has no country specific deviations other than those required by each country’s national codes.
The 5th edition of CAN/ULC 531 was published in 2024, although an effective date has not yet been established by testing and certification laboratories (e.g., UL Solutions, CSA, and Intertek/ETL). Manufacturers of smoke alarms for use in Canada won’t have to manufacture to these new requirements until test labs set an effective date or the National Building Code of Canada references this new edition. Note that the US has transitioned to the requirements of this harmonized edition as of June 30, 2024. This article will highlight some of the important changes in this latest edition of the standard.
The most important and impactful change in the 5th edition of ULC 531 is the harmonization of the fire tests. It makes sense that the fire tests are harmonized because of the similarity in building construction, furnishings and potential fire sources between Canada and the US. Essentially, the standard is moving to the fire tests that have been defined in UL 217 and 268 since 2016. These fire tests are intended to simulate a number of potential fire conditions and how smoke alarms and detectors will perform under these conditions. The fire tests must be done in a fire test room that is 6.7 meters wide by 11 meters long with a 3-meter height. The suite of fire tests now includes the following types: shredded newspaper, wood crib, flaming polyurethane foam, smoldering polyurethane foam, and smoldering wood.
The polyurethane fires were added to the UL 217 and UL 268 standards in 2016 in an effort to make smoke alarms and detectors more responsive to a broader range of fires, including those involving synthetic materials. Numerous independent research studies had shown that escape time in fires had precipitously decreased over the decades. The reduced escape time has been caused by synthetic materials used in home and office building construction, furnishings, open floor plan buildings, and more.
ULC 531 and UL 217 have traditionally had different methods for measuring the sensitivity of smoke alarms. Despite each standard requiring a type of smoke box to test smoke sensitivity, there were differences in terms of the smoke source and build-up rate permitted within the box. The 5th edition of ULC 531 standardizes measurement of smoke alarm sensitivity in the smoke box defined in UL 217. The smoke source is a cotton wick (or aerosol generator) that produces a nominal 0.3 micron nominal particle size.
Beyond the fire tests, a cooking nuisance smoke test was added, sometimes referred to as the “burger test.” The nuisance test was added to prevent smoke alarms from being too sensitive based on their required response to the new fires. Cooking is by far the most common reason for nuisance alarms and subsequent device deactivation. The cooking nuisance smoke test consists of broiling two hamburgers on an electric range 10 feet from the smoke alarms. In order to avoid a situation where smoke alarms are made completely insensitive to real fires during the nuisance test, a polyurethane fire is lit at the end of the cooking nuisance smoke test and the smoke alarm has to go into alarm in the presence of the cooking nuisance. The net result of these changes is that smoke alarms have a narrower operating range for sensitivity than they used to.
The US National Institute of Standards and Technology (NIST) recently completed a study and published a report (NIST Technical Note TN 2305) on the performance of smoke alarms that were manufactured to the most recent requirements. Specifically, the research looked at the performance of the new smoke alarms versus legacy smoke alarms in a variety of cooking scenarios in a mock kitchen. The tests showed that the new smoke alarms performed as well as the legacy smoke alarms to these nuisances despite having much greater sensitivity to flaming and smoldering synthetic material.
Another major change to the standard in the 5th edition is the harmonization of the audibility requirements for the integral sounder. Previously, the Canadian and US standards had different methods for assessing the sound output of audible devices. In the 4th edition of ULC 531, it was required that audibility be tested in an anechoic sound room. The new edition requires that sound be measured in a reverberant room. While the details about each room will not be covered in this article, it has been determined that measurements in a reverberant sound room are more repeatable than an anechoic room and so it was used as the harmonized requirement going forward.
Beyond just Canada and the US, interested stakeholders are now looking to harmonize requirements with Mexico. Mexico is at the beginning stages of adopting robust fire and life safety codes and standards and they are building upon the foundation created by the efforts of Canadian and US technical committee members. It is quite likely that we will see tri-national standards for fire products for use in North America in the near future.
Achieving the goal of a harmonized Canadian-US smoke alarm standard has been a major accomplishment by all those involved with standardization on both sides of the border. It has required a major effort by UL Standards, manufacturers, test laboratories, and other stakeholders. The harmonized standard will produce dividends for the fire industry for many years to come. And public safety is ultimately improved when new state-of-the-art products such as smoke alarms are installed in the new and retrofit construction of fire alarm systems in buildings. In Canada, smoke alarms are recommended to be replaced at least every 10 years.
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