Objective To evaluate the effectiveness of the immersion protection requirements of a voluntary safety standard for portable handheld hair dryers in preventing electrocution deaths in the USA.
Methods The present work was an interrupted time series study design. Data on annual hair dryer-related electrocution deaths resulting from water contact were developed for the 1980–2007 study period. A multivariate Poisson regression model for rate data was used to evaluate the impact of the immersion protection requirements during the post-intervention period. The analysis controlled for the estimated number of hair dryers in use and the estimated number of US homes equipped with ground fault circuit interrupters, safety devices that would address hair dryer electrocutions even in the absence of the immersion protection requirements of the voluntary standard. The implementation of the 1987 and 1991 immersion protection requirements of the voluntary standard for portable handheld hair dryers was the intervention studied. The main outcome measure was the estimated reduction in the hair dryer electrocution rate associated with the immersion protection requirements of the voluntary standard.
Results After controlling for covariates, the immersion protection requirements were estimated to reduce the rate of hair dryer immersion electrocution deaths by 96.6% (95% CI, 90.8% to 98.8%). This suggests the prevention of about 280 immersion electrocution deaths involving hair dryers during the post-intervention period (1987–2007).
Conclusions The immersion protection requirements of the voluntary safety standard for hair dryers have been highly effective in reducing hair dryer electrocutions.
- hair dryers
- poisson regression
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Portable handheld hair dryers are electrical appliances that operate by creating a flow of air over a self-contained heating element. They typically have a barrel-like body with a pistol grip handle and a power switch that turns the unit on and off. Because they contain uninsulated open-coil heating elements, an alternative current flow path can be created easily when the heating element contacts water, posing an electrocution risk to users holding or retrieving dryers or touching the same water source.
Before the mid 1980s, handheld hair dryers provided no protection from electrocution when immersed in or contacting water. Because they are usually used in bathrooms near water sources, the increased use of hair dryers during the 1970s and 1980s also led to an increase in deaths from electrocution. An early study identified 57 hair dryer electrocution deaths in the USA involving water immersion in baths from 1979 through 1982, an average of about 14 annually; 37 (64.9%) of these involved children under age 10 years.1 US Consumer Product Safety Commission (CPSC) staff estimated an annual average of about 17 electrocution deaths involving handheld hair dryers from 1982 through 1986; more than 90% involved water immersion and about 60% involved children under age 10 years.2 Electrocution scenarios typically involved users retrieving hair dryers dropped into a bath or children playing in baths with plugged-in hair dryers.2 ,3
Beginning in the 1980s, CPSC staff collected information on hair dryer electrocution deaths and hazard patterns,2 ,3 and evaluated the role of play behaviour in electrocutions involving children under age 10 years.4 Staff also sponsored research into the development of immersion protection technology for use in appliances, such as hair dryers, and encouraged the early adoption of immersion protection requirements in the hair dryer voluntary standard.2
The voluntary standard was developed under the auspices of Underwriters Laboratories Inc. (UL), an independent product safety certification organisation that works with industry to develop consensus safety standards.5 Beginning in October 1987, the voluntary standard for handheld hair dryers, UL 859,6 required immersion protection for hair dryers plugged into electrical receptacles, but only when the power switch was turned off. This requirement was met with sealed power switches that prevented current leakage from turned-off hair dryers and addressed electrocutions occurring when users retrieved turned-off dryers dropped into water. However, the requirement did not address electrocutions when the dryers were switched on. Nor did it address immersion electrocutions that resulted from children's play involving the power switch.3 ,4
The voluntary standard was later amended and, beginning in January 1991, required full immersion protection: ie, protection when the power switch was turned either on or off. Full immersion protection was provided by integrating circuit interrupters into the power supply cords of hair dryers.7 These circuit interrupters are clearly visible as the block-shaped plugs that connect to electrical receptacles.
The purpose of this study is to evaluate the effectiveness of the immersion protection requirements of the voluntary safety standard in preventing electrocution deaths associated with handheld hair dryers. For the remainder of this analysis, the term electrocution refers only to deaths, not non-fatal injuries from electrical shock.
Study design and sources of data
The study used an interrupted time series design to estimate the reduction in the annual hair dryer electrocution rate associated with the immersion protection requirements of the voluntary standard. Data for the analysis were based on annual estimates of reported immersion electrocutions involving handheld hair dryers compiled by CPSC staff for the years 1980 through 2007. The major information source was the CPSC's Death Certificates database. The CPSC contracts with each of the 50 states and the District of Columbia to purchase information on unintentional deaths with external causes that have a high probability of being product related. Prior to 1999, hair dryer deaths were coded under the general E-code category E925, ‘Accident caused by electric current’ based on the WHO's International Classification of Diseases, ninth revision (ICD-9).8 Beginning in 1999, under ICD-10,9 hair dryer deaths were coded under category W86, ‘Accident caused by electric current: Other specified electric current’, or W87, ‘Accident caused by electric current: Unspecified electric current’. Although ICD-10 codes generally varied from those in ICD-9, the electrocution codes were consistent: electrocutions coded under W86 or W87 in ICD-10 also would have been those coded under E925 in ICD-9.10 Hair dryer deaths within these ICD codes were identified by the short description of the incident provided on most death certificates, including details on hair dryer and water involvement.
Cases were also collected from the CPSC's Injury and Potential Injury Incidents database. This database draws on reports of injuries, deaths and potential injuries from news media accounts, reports from the Medical Examiners' and Coroners' Alert Project (MECAP),11 reports from the public via the CPSC's telephone hotline or website, and other sources.
To ensure the accuracy of the death reports and to collect additional information on incident scenarios, CPSC staff conducted, as needed, follow-up in-depth investigations on the hair dryer deaths. These included collecting police and coroner reports, discussions with police investigators and medical examiners, and (sometimes) discussions with next of kin. Duplicate cases, such as those that might be reported to the CPSC from multiple sources, were eliminated from the analysis, as were hair dryer electrocutions not involving water contact.
Because information on the population of hair dryer users is unavailable, the number of hair dryers in use was used as the primary measure of risk exposure. The annual number of hair dryers in use was estimated with the CPSC's Product Population Model, a computer model that projects the number of products in use, given estimates of annual product sales and product failure rates.12 Hair dryer sales were based on estimates of industry shipments to retailers.13–17 The hair dryer failure rate (ie, the rate at which hair dryers go out of use) was assumed to follow a γ distribution, a commonly used distribution for the failure of products that last only a few years, with an expected product life of about 4 years.12 ,18 This failure rate suggests that about 60% of hair dryers will have failed after 4 years of use; and more than 95% will have failed after 10 years of use.
The effectiveness of the immersion protection requirements was evaluated with a log linear Poisson regression model for rate data. The response variable, the annual estimate of hair dryer immersion electrocutions, was assumed to follow a Poisson distribution and was estimated as a function of several explanatory variables and an offset term.21 ,22 The offset term adjusts the expected value of the response variable for an indexed measure of risk exposure. For this analysis, the offset term was the estimated number (in millions) of portable hair dryers in use, a direct measure of risk exposure, and the electrocution rate was defined as the number of electrocutions per million hair dryers in use. All variables were included in the analysis as annual estimates.
Two primary explanatory variables were used to determine the effectiveness of the hair dryer standard. The first was the proportion of hair dryers in use subject to the immersion protection requirements adopted in 1987 (‘Standard 87’), which provided protection only when the power switch was switched off. The second was the proportion of hair dryers in use that were subject to the additional requirements adopted in 1991 (‘Standard 91’), which added protection when the power switch was switched on. These variables ranged from 0, in the years before the requirements went into effect, to 1, when all hair dryers in use were subject to the requirements. For example, the proportion of hair dryers subject to the requirements for full immersion protection in 1994 was estimated as the number of hair dryers in use in 1994 shipped on or after January 1991, divided by the total estimated number of hair dryers in use in 1994.
We also included a variable representing the use of ground fault circuit interrupters (GFCI) in the US housing stock. GFCIs are electrical devices that, if installed in household branch circuits, can prevent electrocutions by detecting ground faults and interrupting the flow of electric current from those circuits. Homes built with GFCIs in bathrooms provide protection from hair dryer immersion electrocutions, even without the hair dryer circuit interrupters. In 1975, the National Electrical Code (NEC) was revised to require GFCI protection in new construction and renovated bathrooms.23 ,24 We therefore included a variable representing the proportion of the housing stock built after 1975 (‘GFCI’) as a measure of homes built with GFCIs. It is approximate because local building codes do not always incorporate all NEC provisions or may lag behind the current edition. Nor does it adjust for GFCIs added during bathroom renovations. Nevertheless, GFCI is included to account for hair dryer electrocutions that would have been prevented even without the hair dryer voluntary standard.
A total of 185 hair dryer electrocutions were identified during the 1980–2007 study period. CPSC staff conducted follow-up, in-depth investigations in 88 of the cases. A total of 21 non-immersion hair dryer electrocutions were identified and excluded from the analysis because they would not have been addressed by the immersion protection requirements of the voluntary standard. The analysis is based on the remaining 164 cases involving immersion-related electrocutions.
A total of 105 deaths (64.0%) involved children under age 10 years (table 1). Males accounted for 57.1% of victims under age 10, but only 32.2% of victims age 10 and older. A total of 153 electrocutions (93.3%) occurred in baths; of the remaining 11, 3 occurred in showers, 3 on wet floors, 1 involved a water-filled sink and 4 occurred in unknown locations.
Hair dryer electrocutions, by year, are shown in figure 1. These data suggest a rapid decline in deaths beginning in the mid to late 1980s, at about the time the immersion protection requirements went into effect. Prior to the 1987 immersion protection requirements, there were about 15.7 electrocutions annually; following the 1991 requirements there were only about 0.9 electrocutions annually.
Hair dryer shipments ranged from about 17 to 23 million annually during the study period. Figure 2 provides estimates of the annual number of hair dryers in use, ranging from about 68 million in 1980, to about 103 million in 2007.
Table 2 presents the regression results. The deviance and χ2 statistics suggest that the model fits the data reasonably well. The mean deviance (ie, deviance/df) was somewhat <1, suggesting that overdispersion was not a problem. Additionally, based on an evaluation of the standardised Pearson residuals, there was no indication of serial correlation, or a violation of the model assumption of the mean and variance equivalence.25 Figure 3 compares the predicted rate of hair dryer electrocutions with the observed electrocution rate.
The coefficients for Standard 87 and Standard 91 were negative and statistically significant. The coefficient for Standard 87 suggests a reduction of about 77.4% (95% CI 42.4% to 90.9%) in the electrocution rate (ie, electrocutions per million hair dryers in use) associated with the 1987 requirements. The coefficient for Standard 91 suggests a further reduction of about 85.0% (95% CI 60.6% to 94.3%) in the electrocution rate associated with the 1991 requirements. Taken together, the 77.4% reduction associated with the 1987 requirements, in combination with the additional 85.0% reduction associated with the 1991 requirements (ie, 0.774+(1−0.774) × 0.850), suggest an overall 96.6% (95% CI 90.8% to 98.8%) reduction in the immersion-related electrocution rate, relative to the prestandard conditions when there were no immersion protection requirements. The coefficient for the third explanatory variable, GFCI, was negative, as expected, but not statistically significant (p=0.54).
The reduction in the hair dryer immersion electrocution rate is illustrated in figure 4, which shows the predicted (ie, fitted) rate of electrocutions over time, along with what the predicted rate would have been without the immersion protection requirements (ie, when the Standard 87 and Standard 91 explanatory variables were set equal to 0). The vertical distance between the two rate functions after about 2001, when virtually all hair dryers in use provided full immersion protection, represents the estimated 96.6% reduction in electrocution rate associated with the immersion protection requirements. The function representing the predicted electrocution rate in the absence of immersion protection is downward sloping because of the negative coefficient for GFCI. However, the slope represented in the graph is subject to the same variability as the regression coefficient.
Based on the estimated 96.6% reduction in the electrocution rate, the standard would have prevented about 280 deaths from 1987, when the first immersion protection requirements went into effect, through 2007.
In addition to our primary model, table 3 presents regression results for subsets of the population at risk. When the analysis was limited to children under age 10 years, the estimated reduction in the electrocution rate was 96.1% (95% CI 88.6% to 98.7%); when limited to those aged 10 or older, the reduction in the electrocution rate was 97.4% (95% CI 83.8% to 99.6%). When the analysis was limited to females, the estimated reduction was 98.1% (95% CI 92.9% to 99.5); when limited to males, the estimated reduction was 95.1% (95% CI 81.9% to 98.7%). Thus, the results were not altered when limited to selected population subgroups.
Several analyses were conducted to evaluate the sensitivity of the statistical findings to variations in the specification of the regression model. The results were not sensitive to variations in the expected product life of hair dryers. When the model was estimated assuming a 3-year product life, rather than 4 years as in the primary analysis, the immersion protection requirements were estimated to reduce the electrocution rate by 96.0% (95% CI 89.6% to 98.5%); when average product life was set at 5 years, the requirements were estimated to reduce the electrocution rate by 96.5% (95% CI 90.1% to 98.8%).
The results remained unchanged when the expected value of the response variable was adjusted for the US resident population26 instead of the estimated number of hair dryers in use. With this adjustment, the estimated reduction in the electrocution rate was 97.1% (95% CI 95.2% to 98.2%).
Finally, we included in the model a variable representing total US electrocutions, other than those resulting from hair dryer immersions, to account for the possibility that the reduction in hair dryer electrocutions was related to general downward trends in electrocutions, rather than voluntary standard's immersion protection requirements.27 ,28 This variable was not statistically significant (p=0.95); however, when included, the estimated reduction in the hair dryer water immersion electrocution rate was 96.6% (95% CI 94.2% to 98.0%).
This analysis suggests that the voluntary safety standard for handheld hair dryers has been highly effective. Because immersion electrocutions can be virtually eliminated if hair dryers comply with the voluntary standard's immersion protection requirements, the standard's effectiveness is closely tied to industry compliance. Available evidence generally suggests a high degree of compliance. There have been about 16 public recalls of hair dryers since 2000 due to the lack of compliance with the immersion protection requirements.29 However, while these recalls suggest less than full compliance, they accounted for only about 500 000 hair dryers: less than a quarter of 1% of hair dryers shipped since 2000.
Other information also suggests a high level of industry conformance. The market for handheld hair dryers tends to be highly concentrated. In 2007, the top three suppliers accounted for about 92% of shipments to the US market.30 All three of these suppliers are certified as complying with the voluntary standard, as are a large number of smaller suppliers.31 ,32
The high rate of conformance to the voluntary safety standard is related to several factors. Perhaps most importantly, the immersion electrocution hazard has become well known by suppliers and can be readily addressed by including circuit interrupters. Second, manufacturers and retailers of products not conforming to product safety standards are subject to increased product liability claims when their products cause injuries or deaths.33 As a result, many major retailers require that suppliers provide only products meeting existing safety standards.34 In the case of hair dryers, compliance is easily determined by the presence of the large block-shaped plugs that connect to electrical receptacles. Finally, hair dryers that do not conform to the immersion protection requirements are subject to recall by the CPSC. The CPSC's Office of Compliance staff consider hair dryers that do not prevent electrocution when dropped in water to be defective, presenting a substantial product hazard under Section 15 of the Consumer Product Safety Act.35 Consequently, the CPSC has initiated recalls of handheld hair dryers that do not comply with the immersion protection requirements; recalls that are potentially costly to manufacturers.
The primary limitation of this analysis is the possibility of undercounts in estimates of immersion electrocutions. Information on hair dryer electrocutions derived from the CPSC's databases does not necessarily provide a complete count. However, the CPSC has been actively involved in addressing hair dryer electrocutions since the early 1980s, and has attempted to collect information on all deaths resulting from this hazard pattern. Because there is no reason to believe that under-reporting of hair dryer electrocutions has increased in recent years, it seems unlikely that such under-reporting would have materially altered our statistical findings. However, under-reporting may have led to underestimating the number of electrocutions prevented by the immersion protection requirements.
Another possible limitation is the study's reliance on estimates of hair dryers in use, based on industry-provided estimates of the average product life of hair dryers and the assumed distribution of product failures over time. However, our results were not generally sensitive to plausible variations in these parameters, as suggested in the sensitivity analysis.
Finally, the impact of the immersion protection requirements on non-fatal shock injuries was not evaluated in this analysis. Based on reports to CPSC, there are substantially fewer non-fatal electrical shocks than electrocutions. However, non-fatal shocks are probably subject to significant under-reporting: they are less likely than electrocutions to be mentioned in media news accounts and a large proportion of those injured may not even seek emergency medical care. While the analysis does not address the segment of injuries that are non-fatal, such exclusion should not have biased our analysis of electrocutions. Additionally, we note that, as with deaths, reported non-fatal electrical shocks involving hair dryers also exhibited a rapid decline following requirements for immersion protection.
This analysis suggests that the hair dryer voluntary standard's immersion protection requirements have been highly effective in reducing electrocutions. Based upon our analysis, they may have reduced the hair dryer-related immersion electrocution rate by an estimated 96.6%, and may have prevented about 280 deaths during the approximately 20-year time span from 1987 through 2007.
What is already known on the subject
Prior to the mid 1980s, when portable handheld hair dryers provided no protection from electrocution when immersed in water, there were an estimated 15 electrocution deaths annually in the USA involving hair dryer water immersion.
Electrocution scenarios typically involved users retrieving hair dryers after having dropped them into a bath or children playing in baths with plugged-in hair dryers.
The voluntary safety standard for hair dryers adopted requirements that were intended to provide partial immersion protection in 1987, and additional requirements that were intended to provide full immersion protection in 1991.
What this study adds
The results of this study suggest that the immersion protection requirements of the voluntary standard reduced the hair dryer immersion electrocution rate by about 96.6% and prevented about 280 immersion electrocution deaths in the USA during the post-intervention period (1987–2007).
The voluntary standard for hair dryers has been highly effective in preventing water immersion electrocutions.
Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Disclaimer The views expressed in this article are those of the authors. It has not been reviewed or approved by and may not necessarily reflect the views of the US Consumer Product Safety Commission. Because this article was written in the authors' official capacities, it is in the public domain and may be copied freely.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The data used in the analysis is available by contacting SG ( ). No individuals are identifiable from the database; all information is anonymous.