UL Safety Standards UL 2157, 3rd edition, Electric Clothes Washing Machines and Extractors, and UL 2158, 4th edition, Electric Clothes Dryers, provide three methods to comply with entrapment requirements and a manufacturer can choose either one of these methods to evaluate their appliance. One of these methods is found in Clause 15.6.1.b) (UL 2157) and Clause 17.6.1.b) (UL 2158):

“If a household front-loading appliance has an opening into the clothes drum that will permit the entrance of a 203 mm diameter sphere and a clothes drum with a volume of 60 L or more, then the appliance shall be investigated with respect to the ventilation it provides.”

Young children have been known to enter the drum of these laundry appliances (e.g. to play “hide-and-seek”), and some have died over the years due to suffocation. So, the intent of these entrapment requirements is to mitigate the risk of suffocation that could lead to a child’s accidental death in the event that they become trapped inside of a clothes dryer or washing machine.

Proposals for test methods related to investigating the amount of ventilation these appliances provided were made in 1974 and 1975 , but these were never implemented in either UL 2157 or UL 2158 due to disagreement, with industry members, at the time.

UL Research & Development Project

UL LLC’s Fire R&D team was requested to develop a test to evaluate a washer or dryer’s ventilation. You may wonder why UL’s Fire R&D team was requested to conduct this type of work on these types of electrical appliances, where the particular risk prevention being studied was not related to a potential fire hazard. A large amount of fire protection research has reported the cumulative effects of decreasing Oxygen and increasing Carbon Dioxide concentrations, as well as toxic substances, resulting from fires. This research was applied to develop a test to evaluate ventilation because people consume Oxygen and release Carbon Dioxide similar to a very small fire.

The research objectives of the investigation were to:

  1. Develop a mimic of an entrapped child, in terms of heat generation, Oxygen consumption, and Carbon Dioxide production.
  2. Develop a procedure to use the mimic data in a representative clothes washer and dryer.
  3. Present hazard assessment information that may be used to establish acceptance limits.
  4. Develop a test method and compliance criteria for investigating an appliance, with respect to the ventilation it provides, that can be proposed to the UL Standards Technical Panel (STP) for future inclusion into the UL 2157 and UL 2158 Safety Standards.

Technical Approach

A UL Research project was designed to mimic the heat generation, Oxygen consumption, and Carbon Dioxide production of a child entrapped in either a clothes dryer or washer. A Bunsen burner using methane gas placed inside the drum of the appliance was used to mimic the rate of Oxygen consumption and heat generation. Carbon Dioxide (CO2) was added to the sample air in the drum to make up for the CO2 production of a child.

Parameters were chosen to provide a range of values for Oxygen consumption, CO2 generation, and heat generation (Watts). The child mimic used had the same characteristics as a 6 year old boy in the 95% percentile weighing about 60 pounds. This age of child was chosen in order to displace the largest amount of air once the child mimic is inside the washer or dryer. The density of a human is slightly less than water (61.5 lbs/ft³), resulting in a displaced volume of 0.98 ft³.

Literature Review

Various references were consulted in order to specify the minimum rates of Oxygen consumption and CO2 production of a child. Purser has develop a Fractional Effective Dose (FED) model that can be used to estimate the time to incapacitation due to increased CO2 and decreased Oxygen concentrations.

Standard Revision

As a result of the research project, UL is leading a laundry appliance industry Task Group in the development of a standard revision proposal to revise both UL 2157 and UL 2158 to include entrapment and ventilation requirements. This work is based on the above mentioned UL Research project, and is anticipated to be concluded in late 2017. The work includes establishing a test method to calculate the amount of ventilation a laundry appliances provides, determining the appropriate child mimic to use, and the establishment of compliance criteria related to the Oxygen and CO2 levels intended to prevent suffocation.

After the proposal is completed, it will be submitted to the UL 2157/UL 2158 STP for review, comment, and balloting for inclusion in these two laundry appliance standards.

Using the output of UL’s Research project to positively impact a UL Safety Standard, and working with an industry Task Group, have proven to be an effective means to propose a change in requirements that are intended to increase the level of safety in these two UL Standards.

For more information or questions regarding this topic, please contact Darrin Conlon at


1Ventilation of Clothes Dryers, Subjects 560, 1206, 1240, Jan 3, 1974
2Test for Clothes Dryer Compartment Ventilation without Combustion of Fuel, Subject 560, Jan 9, 1975
3Julia A. McMillan MD and Ralph David Feigin MD, Oski’s Solution: Oski’s Pediatrics: Principles and Practice, Fourth Edition, Apr 17, 2006, Ch 14 “Feeding the Healthy Child”
6Purser D.A. Assessment of Hazards to Occupants from Smoke, Toxic Gases and Heat. The
SFPE Handbook of Fire Protection Engineering 4th ed),.DiNenno P.J (ed.), National Fire Protection Association, Quincy, MA 02269, 2009, pp. 2/96 – 2/193

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