Reducing Injury and Damage Related to Electric Dryer Fires
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Reducing Injury and Damage Related to Electric Dryer Fires

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Despite their widespread use in U.S. homes, clothes dryers are involved in a significant...

Despite their widespread use in U.S. homes, clothes dryers are involved in a significant
number of residential fires. According to some estimates, dryer fires produce annual
U.S. property losses approaching $100 million, and lead to multiple consumer deaths and hundreds of injuries. Proper installation and effective maintenance of clothes dryers can significantly reduce the risk of appliance-related fires. But recent research has shown that product construction and design considerations are also important elements in building safer dryers.
This UL white paper reviews research by UL and others that has resulted in the development of testing requirements included in the revised second edition of UL 2158, the Standard for Safety for Electric Clothes Dryers. The white paper then discusses
the fire containment requirements, identifying potential design considerations for manufacturers, and the importance of testing a variety of alternate materials and
components to meet the requirements for compliance. The white paper concludes with
a discussion of the potential benefits for manufacturers, retailers and consumers when
the fire containment requirements become effective in March 2013.

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Reducing Injury and Damage Related to Electric Dryer Fires Reducing Injury and Damage Related to Electric Dryer Fires Document Transcript

  • Reducing Injury and DamageRelated to Electric Dryer FiresFire Containment Tests for the Second Edition of UL 2158
  • Reducing Injury and Damage Related to Electric Dryer FiresReducing Injury and Damage Related to ElectricDryer Fires: Fire Containment Tests for the SecondEdition of UL 2158Despite their widespread use in U.S. homes, clothes dryers are involved in a significantnumber of residential fires. According to some estimates, dryer fires produce annualU.S. property losses approaching $100 million, and lead to multiple consumer deathsand hundreds of injuries. Proper installation and effective maintenance of clothesdryers can significantly reduce the risk of appliance-related fires. But recent researchhas shown that product construction and design considerations are also importantelements in building safer dryers.This UL white paper reviews research by UL and others that has resulted in thedevelopment of testing requirements included in the revised second edition of UL 2158,the Standard for Safety for Electric Clothes Dryers. The white paper then discussesthe fire containment requirements, identifying potential design considerations formanufacturers, and the importance of testing a variety of alternate materials andcomponents to meet the requirements for compliance. The white paper concludes witha discussion of the potential benefits for manufacturers, retailers and consumers whenthe fire containment requirements become effective in March 2013.The Causes and Consequences an average of 210 injuries and 10 deathsof Dryer Fires each year.1Statistics compiled by the U.S. Consumer In more recent years, there has beenProduct Safety Commission (CPSC) a reduction in the number of dryer-relatedconfirm that fires involving clothes dryers residential fires, but an increase in theare numerous and costly, and occasionally value of lost and damaged property.result in deadly consequences. According According to comparable CPSC data forto data collected by the Commission, the period between 2006 and 2008,there were an average of 8000 there was an annual average of 7000dryer-related residential fires annually dryer-related fires in the United States,between 2002 and 2004. These fires 1000 fewer than the 2002-2004 period.resulted in estimated annual property However, these fires resulted in estimateddamage of $81.7 million, and caused annual property damage of $91.8 million,page 2
  • Reducing Injury and Damage Related to Electric Dryer Firesa 12% increase from the 2002-2004 also played a role in reported dryer fires. between the CPSC, AHAM, UL andperiod, causing an average of 230 injuries Importantly, AHAM reported that, “in other interested parties, the taskeach year, a 10% increase.2 91% of the incidents investigated, the group focused on the development accumulation of lint on the screen was of a protocol for testing the fireThe causes of electric dryer fires havebeen extensively researched over the less than 25%.” 4 containment capabilities of clothespast decade by the CPSC, industry dryers, and on the identification of Consumer behavior has also beenassociations including the Association of acceptable testing parameters. identified as a factor in dryer fires.Home Appliance Manufacturers (AHAM), In addition to allowing lint and fibers to The task group’s efforts resulted inindividual appliance manufacturers, and accumulate in a dryer filter and venting the development of two separate firestandards organizations including UL. Yet, system, an equally significant fire risk can containment tests. In the first of thesewhile some research has pointed to the result from the drying of certain types tests, the drum load fire containmentaccumulation of lint and the subsequent of materials. According to data from the test, the exterior of each sample dryer isreduction of air flow as a primary cause U.S. Fire Administration’s National Fire draped with a single layer of cheesecloth,of dryer fires, other testing has supported Information Resource System (NFIRS), covering the top, bottom, front, backclaims that the cause of dryer fires can be the buildup of lint, dust and fiber and and sides of a dryer. (Cheesecloth isattributed to a number of factors. the drying of wearing apparel, including highly flammable, so any damage to theIn its “Final Report on Electric Clothes synthetic or contaminated materials, cheesecloth wrapping is deemed to beDryers and Lint Ignition Characteristics” were the primary ignition sources in over evidence of a dryer’s inability to containpublished in May 2003, the CPSC focused half of U.S. residential dryer fires during a fire.) The dryer drum is then loaded withon the buildup of lint in or near a dryer’s the period from 2002 to 2004. 5 cloths with a dry weight equivalent toheating elements. According to the CPSC one pound of cloth for each cubic foot of While increased consumer educationreport, “lint that accumulates inside dryer drum volume. The cloths are then regarding these risks can help reducethe dryer can ignite if the lint contacts ignited with a propane torch, the dryer the number of dryer fires, recent researchcertain areas of the heater housing, if door closed, and the exterior cheesecloth has focused attention on the design ofthe lint is in proximity to the heater, or if repositioned to ensure complete coverage dryers themselves, and the ability oflint is ingested by the heater box.” CPSC 3 of the dryer. a dryer unit to actually contain a fire,research also found that the accumulation In the second test, the base lint fire should one occur. This research has ledof lint around a heater housing can ignite containment test, the exterior of each to important changes in UL’s safetywhen a dryer exhaust vent is blocked and sample dryer is again draped on all sides Standard for electric clothes dryers thata dryer’s high-limit thermostat fails. with a single layer of cheesecloth, and will help minimize property damageBut a study on clothes fire dryer incidents caused by dryer fires and mitigate risks loaded with cloths with a dry weightpublished by AHAM in 2002 refuted the to consumers. equivalent to one pound of cloth for eachnotion of lint as the primary contributor cubic foot of drum volume. In addition,to dryer fires, arguing instead that Research on Dryer Fire all electrical components and connectorsdryer fires can be linked to a number Containment Issues located in base of a dryer unit are coveredof potential factors. Based on a careful The most significant work on dryer fire with eight layers of cheesecloth toevaluation of 191 clothes dryer fire containment was produced by a joint simulate the accumulation of lint. Theincidents during a six month period in task group, consisting of representatives internal cheesecloth in the base is then2001, AHAM determined that factors from UL, CSA, and several major appliance ignited, and the exterior cheeseclothsuch as a dryer load, a dryer’s electrical manufacturers. Formed in late 2002 repositioned to ensure complete coveragesystem, and a dryer’s mechanical system following ongoing extensive discussions of the dryer.page 3
  • Reducing Injury and Damage Related to Electric Dryer FiresBoth drum load fire containment testing and base lint fire containment testing areconducted with the drum in a rotating condition (simulating a dryer in actual operation)as well as in a static condition (simulating a dryer that has completed a drying cycle).A separate dryer sample is used to test for each condition. If any portion of the exteriorcheesecloth ignites prior to the seven-hour test time limit, the test sample is deemed tohave failed the test.Following the development of the fire containment tests, members of the jointtask group then conducted independent testing of products according to the testprotocols to validate the approach and testing parameters. UL contributed to thiseffort by conducting its own testing in 2004 and 2005 to determine whether the newlydeveloped tests would better assess a dryer’s ability to contain a fire. In UL’s testing,only 28% of the units tested did not ignite the exterior cheesecloth, thereby helping tosubstantiate the importance of the fire containment tests in evaluating the safety ofelectric dryers.The testing by UL and other members of the joint task group ultimately led to therecommendation to incorporate the drum load fire containment test and the base lintfire containment test into UL 2158. These tests were incorporated into a revised versionof the second edition of UL 2158, issued in March 2009. Manufacturers seeking orwishing to maintain certification to UL 2158 will need to demonstrate compliance withthese additional tests before March 20, 2013.Dryer Design Issues Potentially Affecting ComplianceManufacturers can increase the likelihood of compliance with the fire containmentobjectives of UL 2158 by considering certain design aspects of their dryer models inadvance of testing. Specifically, the use of plastics and other polymeric materials indryer components, the position of ventilation openings, and the presence of openingsin the bottom of the dryer can directly affect the potential for dryer fires to develop,and can speed or impede their spread. Careful evaluation of design options during theproduct development stage can mean the difference between complying with the firecontainment tests and achieving certification, or failing the tests and reevaluatingalternative approaches and configurations.Plastics and polymeric materials are commonly used in a variety of dryer components,including drum baffles, fans and fan housings, and lint screens and frames. Dependingon their use in the final dryer assembly, UL 2158 requires that these materials meet oneof three flammability classifications found in UL 94, including HB (for horizontal burn),as well as the more stringent 5VA or 5VB classifications. However, HB-rated materialsmay ignite more quickly under the base lint fire containment test or the drum load firecontainment test, allowing hot, molten plastic to flow throughout the unit and escapefrom the dryer cabinet. Alternatively, the melting or deformation of parts formedof thermoplastic materials may create unexpected openings in the fire enclosure,allowing flames or other burning materials to escape, or for fresh air to reach materialssmoldering within the dryer cabinet.page 4
  • Reducing Injury and Damage Related to Electric Dryer FiresIn evaluating the use of polymeric for the bottom of a dryer cabinet can lead additional models are identical to thosematerials in dryer components, to a reduction in the number of openings, in the initial model tested.manufacturers should consider the and the remaining openings can then be A group of clothes dryer models may beintended location of components to shielded or otherwise blocked. covered by testing representative samplesdetermine whether their use increases Other design modifications or changes to address the worst case conditions. Inthe risk of fire or has the potential to that may improve the likelihood of order to choose representative samplescontribute to a fire’s spread. Polymeric complying with UL 2158’s fire containment from the various models and constructionsmaterials may need to be replaced with tests include closing or shielding other produced by a manufacturer, it ismetal parts or otherwise shielded to openings in a dryer cabinet or base with important to understand the differencesprotect them from flames originating noncombustible materials, and the use of between models and consider allfrom within a dryer. In addition, stronger and more fire-resistant seals and alternative constructions.manufacturers should evaluate the use gaskets. Additional modifications that canof HB-rated materials in general, and mitigate the risk of fire may be possible, Some common areas of constructionmay need to utilize materials that depending on the unique characteristics variation within a line of clotheshave a more stringent fire resistance of each dryer model submitted for testing. dryers include:classification to comply with the dryer Alternative Polymeric Materials — Ultimately, design options to decrease thefire containment requirements. likelihood of dryer fires and to increase When various materials are utilized forThe position of ventilation openings in consumer safety must also account for polymeric parts, the fire containmenta dryer cabinet and their proximity to dryer performance, manufacturing and tests should be conducted with eachcombustible materials and potential costs. Each manufacturer will need to material specified. Initial testing may beflame spread should also be evaluated. thoroughly evaluate all options, including conducted with the material with theAlthough UL 2158 requires that ventilation their impact on safety, and their eventual lowest temperature and flammabilityopenings be equipped with louvers cost to determine the best approach. ratings to determine if the partor other types of barriers to limit the UL has the requisite resources and experiences charring, igniting, melting orlikelihood of expulsion of burning expertise that can provide a framework deforming. If the part is unaffected, thereinsulation, flames and burning material for this process and expedite the is no need to test additional materials.may still escape a dryer cabinet under analysis required. In determining the worst case materialactual fire conditions. Determining Representative for testing, it is important to note thatSpecial attention must be given to Dryer Samples for Testing the flammability rating of a materialopenings in the bottom of a dryer unit. The complexity of fire containment is a threshold rating. This meansUL 2158 restricts the individual and tests will typically require testing of a that different materials with thecumulative size of unused openings in a minimum of four dryer samples for each same flammability rating may reactbottom enclosure. However, under the dryer model being certified to UL 2158. differently when exposed to the dryerrigors of the base lint fire containment Once an initial dryer model has been fire containment tests. For example,test in UL 2158, previously inconsequential tested, additional models from the same one material may not ignite at allopenings may provide oxygen to flaming manufacturer may require fewer samples. while another material with the sameparts or permit passage of flaming or The actual number of dryer samples flammability rating may ignite briefly ormolten materials, thus leading to ignition required for testing will depend on the burn steadily. Therefore, it is important toof the cheesecloth during the testing. product configuration and whether the determine if the part was impinged uponMore strict fabrication quality standards materials and components used in the by flames during testing.page 5
  • Reducing Injury and Damage Related to Electric Dryer FiresIt is also important to consider a Drum Size, Opening Configuration and documentation on a dryer’s design,material’s response to the heat produced Airflow — When the clothes drum size including a description of all wiringby a fire. If a part deforms or melts when and/or drum opening configuration routing paths and locations of allexposed to heat, unexpected openings varies, the load fire containment test routing devices. Flammability ratings onmay be created in the enclosure. Such must be conducted with each drum all nonmetallic parts used in a dryer’sopenings can allow additional oxygen size and configuration. In addition, if an construction, such as baffles, lint screens alternate blower results in changes to theto be introduced into an enclosure, and frames, lint screen holders, drum airflow, the load fire containment testcausing a fire to intensify or allowing it to seals, lamp lens, and access panels, must be conducted with each blower.propagate outside of a dryer enclosure. should also be documented and made Front/Rear Controls — For clothes available for review. Further, the materialsBottom Openings — Openings in the dryers with the option for controls to be used in these parts must be controlledbottom of a dryer allow oxygen to be located on the front or rear, the load fire for the specific material manufacturerintroduced into a clothes dryer enclosure, containment test must be conducted and designation, since a change in theand may also allow flames to propagate with both control configurations. material could affect the outcome ofoutside of a dryer enclosure. Although In addition to anticipating the number the fire containment tests. Finally, athe requirements of UL 2158 limit the of test samples required, manufacturers description of any gaps in panels thatnumber of bottom openings, models with seeking UL 2158 certification should make up the outer enclosure isextra manufacturing holes in the bottom also be prepared to provide additional also advised.plate should be selected for the basefire containment test. Most often, thesemodels are the basic models in a serieswith the fewest options.Exhaust Venting Configuration — Forclothes dryers configured to allow eitherrear, side, or bottom venting, the base firecontainment test may need to be repeatedin each venting configuration. This isbecause the placement of cheeseclothin the base will vary depending on thelocation of exhaust venting.Stacked Configurations — Although thetesting of an individual dryer is consideredrepresentative of two identical stackeddryers, the base fire containment testmust be repeated on a stacked washer/dryer combination.Optional Drum Lamp — When a clothesdryer is provided with an optional drumlamp, the load fire containment test mustbe conducted both with and without thedrum lamp.page 6
  • Reducing Injury and Damage Related to Electric Dryer FiresBenefits for Manufacturers, Appliance Retailers and ConsumersThe fire containment tests in UL 2158 have the potential to significantly reduce therisk of electric dryer fires, damage to residential property, and the injury or death ofconsumers. As such, manufacturers and retailers have a unique opportunity to offerconsumers access to safer electric clothes dryers. In addition, the availability of saferdryer models may accelerate the replacement of older dryers, thereby increasing unitsales levels. The advent of safer dryers also presents an ideal environment in which toremind consumers about the importance of regular dryer cleaning and maintenance,reinforcing their role in the overall effort to increase safety.ConclusionThe fire containment testing included in the revised version of UL 2158, ElectricClothes Dryers, will impose new requirements for appliance manufacturers seekingUL certification now through the effective date of March 20, 2013, when all ULCertified electric clothes dryers will need to have demonstrated compliance with thefire containment tests. In addition to the lengthy review process required to assesscompliance with the revised Standard, research by UL and others has shown that asignificant number of current clothes dryer designs are unlikely to pass the recentlyadded fire containment tests without some product modifications.Manufacturers are strongly encouraged to promptly evaluate their products against thefire containment requirements and consider design changes necessary for compliancewith the new requirements well ahead of the March 2013 deadline. Doing so willsupport uninterrupted product certification and continued market access.For more information about the “Reducing Injury and Damage Related to Electric DryerFires: Fire Containment Tests for the Second Edition of UL 2158” white paper, pleasecontact Michelle Anderson, Principle Engineer – Kitchen & Laundry Machines - atMichelle.Andersen@ul.com1 “2002-2004 Residential Fire Loss Estimates.” Directorate for Epidemiology. U.S. Consumer Product Safety Commission, Jul. 2007. Web. 17 Sept. 2011. http://www.cpsc.gov/LIBRARY/fire04.pdf2 “2006-2008 Residential Fire Loss Estimates.” Directorate for Epidemiology. U.S. Consumer Product Safety Commission, Jul. 2011 Web. 17 Sept. 2011. http://www.cpsc.gov/LIBRARY/fire08.pdf3 “Final Report on Electric Clothes Dryers and Lint Ignition Characteristics.” U.S. Consumer Product Safety Commission, May 2003. Web. 17 Sept. 2011. http://www.cpsc.gov/library/foia/foia03/os/dryer.pdf4 “AHAM Analysis of Industry Data on Clothes Dryer Fire Incidents.” Association of Home Appliance Manufacturers, Aug. 2002. Web. 25 Sept. 2011. http://www.cpsc.gov/library/correction/electric.pdf5 “Clothes Dryer Fires in Residential Buildings.” Topical Fire Research Series. Volume 7, Issue 1. U.S. Fire Administration, Jan. 2007. Web. 24 Aug. 2011 http://www.usfa.dhs.gov/downloads/pdf/tfrs/v7i1.pdf©2011 Underwriters Laboratories Inc. All rights reserved. No part of this document may be copied or distributed without the priorwritten consent of Underwriters Laboratories Inc. 12/11page 7