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Risk of injury per hour of exposure to consumer products
Accid. Anal. and Prev., Vol. 28, No. 1, pp. 115-121, 1996 Elsevier Science Ltd. Printed in Great Britain
Pergamon
RISK OF INJURY PER HOUR OF EXPOSURE CONSUMER PRODUCTS
TO
GORDON HAYWARD Consumer Safety Unit, Department of Trade and Industry, London SWlE 6SW, U.K. (Received
5 August 1993; accepted 15 June 1995)
Ah&act-The aim of this study was to determine and compare the risk of injury per hour of use for a range of consumer products. Exposure data was derived from interviewing a large sample of adults about their use of 76 common kitchen, do-it-yourself and household products. This was combined with hospital sample data for injuries involving each product, to yield the risk-of-injury-per-hour-of-use. Powered cutting equipment, access equipment (ladders and scaffolding) and products with sharp blades were shown to have a comparatively high risk, along with cycles, sunbeds, creosote, cement, car jacks and exercise weights. Perceived risk was shown to be a poor basis for priority setting, but a practical guide to priority for preventive action can be provided by “mapping” products on a plot of the risk of injury per hour of use vs the total medical costs of such accidents. Keywords-Risk, Exposure, Consumer products, Tools, Perceived risk, Medical costs, Home accidents, HASS, Priority setting, Incapacity time
Nor is there a generally accepted and easily determined parameter of injury severity combining fatal and non-fatal injuries. The measure of injury used in this study was therefore the number of patients treated at hospitals irrespective of severity, and the measure of cost was the cost of their medical treatment. The crudest measure of exposure that could be used is simply elapsed time (for example, the probability of injury from a particular cause during one year), but generally a person is only exposed to a particular hazard in a particular environment or when engaged in a particular activity. Deriving measures of exposure for domestic life is much more difficult than for the transport and industrial spheres of activity, because tasks may be performed simultaneously, without discrete points in time when one begins or ends (Wood 1976). The total duration of usage of a product during a year was selected as the most appropriate unit of exposure for this study, since most of the products chosen posed a minimal hazard when not in use. This measure is not universally applicable to all types of consumer products and domestic articles (Wood and Saunders 1976), but it was considered to be the most widely applicable for many of the products most frequently involved in accidents to adults. (The study had to be limited to adults because children switch their attention from one article to another so quickly and frequently that it would not be possible to obtain reliable assessments of their frequency or duration of
INTRODUCTION Individuals, societies and (in particular) governments can face choices between a large number of advocated actions to remove or reduce particular hazards, so it is necessary to have some means of prioritizing the hazards for which action is to be considered. The overall costs (medical and social) of injuries are legitimate concerns in making decisions about the safety of consumer products, but they take no account of the danger posed to the individual by a particular item or activity. However, neither the concepts nor the methodology of risk assessment used in other fields are altogether appropriate for the policy area of consumer product safety, so little account has been taken, to date, of the relative risk of injury, other than by intuition. This study aimed (1) to determine and compare the risks of a range of common consumer products used in the home and leisure sphere, and (2) to combine this risk data with estimates of the costs of accidents involving the products to produce an aid for making priority decisions about safety initiatives.
METHODOLOGY Scientifically, the risk of injury is quantified as a measure of injury divided by a measure of exposure to the possibility of injury. For accidents involving most types of consumer product, there simply are not enough fatalities to furnish a reliable measure of risk. 115
116
G. HAYWARD
use of products from interviews with either them or their parents.) 76 consumer products (mainly kitchen or do-ityourself (DIY) tools and household appliances) were chosen to be studied. These were known from the available accident data (see below) to be involved in a considerable number of accidents to adults in the home and leisure sphere. The overall measure of risk adopted for this study was thus the number of hospital-treated injuries per hour that the product was in use (number-ofinjuries-per-hour-of-use). The questions necessary to calculate mean hours of usage were included in the General Omnibus Survey operated by Research Surveys of Great Britain Ltd during February 1989. Sampling was based on two sets of 136 randomly selected sampling points throughout Great Britain. This produced a representative sample of males and females (each from separate households) aged over 16, who were individually interviewed face-to-face in their homes. For each product in turn, respondents were asked how many were owned, hired or borrowed in the household. If at least one was available, respondents were asked how often they themselves used (any of) this particular product, and then how long they used it for on the most recent occasion, “from getting it out to putting it back”. Respondents were asked to pick the answers to these crucial questions from lists on two cards, which gave ranges of frequency and duration in increasing orders of magnitude. In order to obtain reasonable data on the use of each product, and to limit the effort required by respondents, the sample size was varied from 1000 to 4000, according to how widespread each product was thought to be. (Each sub-sample of 1000 was weighted to correct for sampling deviation from the age, sex and social class profile of the population, prior to analysis). In all 7665 adults (53% female, 15% aged under 25, 17% aged over 65) were each asked about a total of up to 30 products, comprising a mixture of common and uncommon (Research Surveys of Great Britain 1989). In addition, respondents were asked to say how dangerous they felt each product was for an adult to use, on a scale of “very dangerous”/“quite dangerous”/“not very dangerous”/“not at all dangerous”. An earlier pilot study (King 1987) had compared this question wording with four other constructs relating to different aspects of the perception of risk of domestic products: how careful they thought they themselves would need to be to avoid having an accident when using the product; how serious the injury might be if they did have an accident; the type of treatment that might be required; and how many
domestic accidents involving each product they thought would occur to adults. The rankings of the products based on each of the five constructs were highly correlated, with perceived danger giving the same ranking as the combination of all five measures. A high correlation between perceived severity of injury and judgements of “precautionary care” required has also been demonstrated elsewhere (Wogalter et al. 1993). The omnibus survey would not have been large enough to provide reliable injury data for the risk calculations for individual products. Instead, injury rates per adult per year from accidents involving these products (excluding occupational and motor vehicle accidents) were derived from the existing hospital-based sample of the Home and Leisure Accident Surveillance Systems-HASS and LASS-which record information from patients attending the accident and emergency departments of a sample of 22 hospitals (only 11 for LASS) representative of the United Kingdom (Department of Trade and Industry 1990). The annual exposure of each respondent to a product in their household was calculated by multiplying the number of occasions per year on which they used the product by how long they used the product on the last occasion. The mean annual exposure figure for all adults in households possessing the product was then calculated, and multiplied by the proportion of households owning the product to give the mean exposure per adult member of the population. (Note that this is not a very meaningful parameter of exposure in itself, but it converts the exposure and injury figures to a common population base.) Estimates of numbers of accidents treated in hospitals per adult member of the population were calculated from the HASS and LASS data for all injuries to adults involving the products under study. (Corrections were made for cases where details such as the power source of the product were not recorded.) The risk of an accident per hour of exposure was finally obtained by dividing the frequency of accidents per adult by the number of hours exposure per year per adult for each product. The responses to the question of how dangerous each product was thought to be were scaled from 1 (not at all dangerous) to 4 (very dangerous). The mean score for each product was calculated to give a surrogate measure of perceived risk. The HASS database has a facility for estimating the duration of incapacity and the medical costs of each case. The calculations take into account the age of the patient, the part of body injured, the type of injury and the length of any period of hospitalization.
Injury risk of exposure to consumer products
This facility was used to derive mean figures for the incapacity and medical cost of accidents involving each of the products in turn. The mean costs were then multiplied by the figures derived above for the number of accidents per adult member of the population involving each product. It was not possible to calculate the social costs of the accidents. To obtain a measure of the distribution of risk, both hours of exposure and numbers of accidents were summed cumulatively across all the products and the “complementarity point” on the “Lorenz curve” (Finkel 1990) obtained. RESULTS The Table shows the products listed in descending order of risk. 79.7% of the accidents involved products that were associated with only 20.3% of the exposure, but it should be remembered that this was a set of products selected because they were known to be involved reasonably often in domestic accidents. For the entire population of consumer products a much higher degree of concentration would be expected. When looking at products displaying the highest risk, it should be remembered that this is not a comprehensive list of consumer products, nor necessarily of those with the highest risk of an accident, and that these findings are of course generalizations and do not necessarily apply to individual models. Nevertheless, it is worth noting that where the risk of an accident is greater than S/million hours, certain groups of products feature most frequently, (1) powered cutting equipment (particularly electrically powered); (2) access equipment (ladders and scaffolding); and (3) sharp blades-knives, saws, chisels and axes (accidents involving knife sharpeners also belong to this group). However, there are also some miscellaneous articles-cycles, sun beds, welding equipment, creosote, cement, training weights and car jacks. There are a number of interesting comparisons between the risk of an accident for similar products using different power sources, for example hedge trimmers (petrol and electric), welding equipment (electric and gas), saws (electric and hand), carving knives (electric and hand), drill braces (electric and hand) and ovens or hobs (electric and gas). Among the products associated with the longest mean duration of incapacity, one group is very prominent-ladders and scaffolding. This is probably because, like baths, they are often involved in serious falls causing fractures or head injuries which are likely to require hospitalization. The Table shows the total medical cost per adult in the population per year, not the cost per case.
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Note that bicycles are the product group associated with the highest medical costs even though this study excludes road traffic accidents (i.e. where a bicycle was in collision with a moving motor vehicle). Accidents to adults involving bicycles cost about g3.7 million worth of medical resources for the United Kingdom as a whole in mid-1980s prices. Ladders and baths also rank highly on total medical costs, having both a high frequency of involvement in accidents and being associated with a long duration of incapacity. The high ranking of craft and carving knives, however, is entirely due to the frequency of accidents involving them, the mean incapacity time being very low. Figure 1 shows that there is only the vaguest of relationships between the number of accidents per head of population and the risk to an individual (correlation coefficient = 0.18), and that the measured risk may be ten times more or less than what would be predicted from assuming a direct relationship to accident rate. For example, accident rates overemphasize the danger of cycles, baths, scissors, ovens, irons, and hot water bottles, while under emphasizing that of scaffolding, chainsaws, creosote, hedge-trimmers and welding equipment. Figure 2 shows that the ranking that adults themselves gave to the relative risk of products was also a rather poor guide to their actual risk of injury (correlation coefficient = 0.47). For example, respondents overestimated the relative risk of blowlamps, chainsaws, electric blankets, scalpels and hand braces, while underestimating the risks of bicycles, wheelbarrows, brushes, cement and baths. DISCUSSION People’s perception of comparative danger of products is clearly an unreliable guide to the actual risk of injury of a product in use. Consideration of which products tend to be over-rated in terms of hazard and those which are under-rated, suggests that people rely over-much on constructs of sharpness and power of products in their perception of danger, rather than on an assessment of the situations that can arise during use of the products, and the likelihood of them doing so. Furthermore, it has been shown elsewhere (Wogalter et al. 1993) that even prompting respondents to analyse accident scenarios does not influence their ranking of products by perceived risk. The need for objective criteria for priority setting is therefore clear. Currently, if any scientific data is used at all as an aid to deciding which consumer product hazards should receive priority attention, the parameters considered are either the number of injuries (fatal or non-
118
G.
Table 1. Exposure,
Product
name
Electric hedge-trimmer Scaffolding _ Electric welding equipment Food slicer Chopper or axe Craft or DIY knife Bicycle Creosote(wood preservative) Sunlamp or heatlamp Electric circular saw Electric grinder/mill Ladder for leanmg Stepladder/household ladder Electric planer Sunbed or solarium Weight-training weights Knife sharpener Car jack Manual carving knife Electric chainsaw Hammer or mallet Chisel Cement powder/wet morter Petrol lawn mower Petrol-driven chainsaw Handsaw Electric carving knife Loft(attic) ladder Scalpel Saucepan(stove-top pot) Gas welding equipment Glue or adhesiieElectric drill I brace) Petrol hedge’trimmer Electric lawn-mower Chip pan/deep fat fryer Razor for wet shaving Garden fork Bath Sewing needle Hand-powered plane Garden shears Electric nylon line trimmer Secateurs (pruning shears) Shower Screwdriver Hand-powered lawn-mower Exercise equipment Wheelbarrow Electric sewing machine Barbeque Spanner(wrench) Manual sewing machine Scissors Deckchair/sun lounger Pliers Tin opener Gas blowtorch or blowlamp Grater/peeler Broom/brush Garden rake or hoe Frying pan Pressure cooker Microwave oven Electric iron
Total accidents (per million persons per year) 83 49 47 29 82 458 699 14 54 46 31 228 379 26 21 111 16 47 217 12 283 106 36 38 7 99 22 30 16 55 6 36 67 2 74 83 49 62 250 88 7 24 10 41 75 98 19 29 30 22 6 48 4 83 44 10 17 3 12 28 16 24 8 21 41
HAYWARD
risk and injury costs of consumer
products
Total exposure (hours of use per person per year)
Risk (accidents per million hours of use)
Perceived risk (rating of l-4)
1 1 1 1 4 22 35 1 4 3 2 19 37 3 2 11 2 5 26 1 39 15 5 6 1 16 5 6 3 13 1 9 19 1 22 26 16 22 93 34 3 10 4 17 33 46 9 17 17 15 5 39 4 76 48 12 21 5 20 47 28 49 19 58 117
104 65 37 23 21 21 20 19 15 15 13 12 10 10 10 10 10 9 8 8 7 7 7 6 6 6 5 5 5 4 4 4 4 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 1 1 1 I 1 1 1 1 1 1 1 1 .5 .4 .4 .4
3.3 3.0 3.2 2.7 3.1 2.8 2.0 2.4 2.7 3.6 2.9 2.6 2.4 2.8 2.6 2.2 2.2 2.6 2.7 3.7 2.0 2.6 1.8 2.6 3.7 2.4 3.0 2.0 3.3 2.5 3.4 2.5 2.6 3.2 2.6 3.0 2.1 2.0 1.7 1.9 2.2 2.2 2.7 2.1 1.6 1.9 2.1 1.8 1.2 1.8 2.4 1.5 1.8 2.2 1.5 1.5 1.6 3.3 1.7 1.2 1.6 2.4 2.3 1.9 2.2
Mean incapacity (per accident)
Total medical cost (per million persons per year)
Cdwl
CUW
6.7 18.0 8.6 5.5 8.0 5.7 13.3 9.6 9.5 9.3 6.7 18.8 19.7 6.8 10.1 13.6 5.0 13.8 4.9 7.0 13.4 6.6 14.0 11.0 9.5 5.4 5.2 16.7 5.1 11.4 9.1 9.8 8.7 9.0 12.1 11.1 7.0 10.0 19.4 6.2 7.6 9.3 9.0 7.8 15.4 7.0 13.2 14.3 15.6 7.8 10.8 8.7 8.5 6.6 15.1 10.1 5.8 11.1 4.2 13.3 13.9 10.9 9.7 12.1 12.2
5343 9546 3708 1062 4455 18943 81270 1097 3312 7933 1593 36786 53353 1313 1208 10054 566 4000 8444 527 21145 5192 2698 4476 603 4158 1164 4226 606 3840 296 2988 5556 123 9754 5546 2211 3475 34321 5080 385 1427 525 1942 8315 5139 2035 1341 2868 1037 365 2991 220 3816 3926 535 684 208 408 3160 1691 1562 600 1460 2730 -continued
opposite
Injury risk of exposure to consumer products
119
Table 1. (continued) Total accidents (per million persons per year)
Product name Work bench Hair drier Gas oven Cigarette lighter Electric hob(stove-top) Electric oven Hand-powered drill( brace) Gas hob(stove-top) Knitting needle Hot water bottle Electric blanket
11 11 46 7 31 31 3 24 14 21 6
Total exposure (hours of use per person per year)
Risk (accidents per million hours of use)
35 35 155 33 141 157 17 169 116 239 129
fatal) or their consequent cost to the economy. There may be some justification for this in fields where the preventive actions will be paid for from taxes, but safety improvements to a consumer product will inevitably be paid for through increased prices to the consumers of the particular product, not society as a whole. Attempts to rank products in order of priority based on total accidents or total costs are also highly dependent on how each product category is defined. For example, gas ovens and hobs are frequently (though not universally) manufactured as one product-a gas cooker (stove), but treating them as one
.3 .3 .3 .2 .2 .2 .2 .l .1 .I .O
Perceived risk (rating
Mean incapacity (per accident)
1”:)
[days1
1.5 1.7 2.2 2.2 2.2 1.9 2.5 2.3 1.8 1.8 2.5
16.4 15.5 13.5 9.9 11.2 13.7 7.5 14.4 7.7 13.6 16.3
Total medical cost (per million persons per year)
CUW 924 1117 7334 477 2237 2265 156 5755 624 2302 1552
product category would raise their ranking in terms of total medical costs from 13th to 7th place. This is an inherent problem in trying to use accident cost (or just frequency) to rank consumer products in terms of priority for preventive action. Furthermore, as this study has shown, the number of accidents involving each product is not a good guide to its comparative risk, and leads to a different ordering of priorities, focusing on more common products. Rationally, therefore, the risk of injury to the product user should be considered as at least an important factor, if not the prime one. The study has
1000
100
10 Eke
blanket
1
c]
L
0.01
0.1
1
10
Accident risk per million hours of exposure Fig. 1. Accident rate per year vs accident risk per hour of exposure for consumer products.
100
G. HAYWARD
120
Very
Quite
Not very
Not L at all 0.01
Accident Fig. 2. Perceived
risk vs calculated
risk per million
hours of exposure
risk per hour of exposure
for consumer
products.
100,000
1000
100
Accident Fig. 3. Medical
10
1
0.1
0.01
cost of accidents
risk per million
vs risk of accident
100
hours of exposure
per hour of exposure
for consumer
products.
Injury
risk of exposure
shown that it is possible, for adults, to obtain data for number-of-injuries-per-hour-of-use from a corn@ nation of injury data from a sample of hospitals and exposure data from a large scale household survey. However, the economic cost of injuries cannot be ignored, so overall, the allocation of priorities for preventive action can best be guided by considering the comparative positions of particular products on a plot such as Fig. 3. This shows the risk of an accident to the population against the total cost to an individual using a product of such accidents. What is of interest here is not the lack of relationship (correlation coefficient = 0.15) between the parameters, but the way the Figure provides a twodimensional map as an aid to deciding priorities for action. It is clear that action to prevent accidents involving the products at the top right corner would be highly desirable (if effective actions could be devised) since currently both the risk of an accident and the consumption of medical resources is high. There is no cut off point for including products in such a priority list, but their relative importance decreases towards the bottom left hand corner of the figure. Figure 3 does not, of course, show more than an
important fraction of the consumer products available, but there is a broad range of consumer products
to consumer
products
121
against which others can be compared (assuming accident risk and medical costs can be estimated for them), to provide more appropriate guidance to policy makers.
REFERENCES Department of Trade and Industry. Twelfth annual report of the Home Accident Surveillance System-1988 data. London: DTI; 1990. Finkel, A. M. A simple formula for calculating the “mass density” of a lognormally distributed characteristic: applications to risk analysis. Risk Anal. 10(2):291-301; 1990. King, Y. Risk: exposure and perception pilot study. Internal report, Consumer Safety Unit; 1987. Research Surveys of Great Britain. Omnibus consumer products risk exposure study. Unpublished report to Department of Trade and Industry; 1989. Wogalter, M. S. et al. Risk perception of common consumer products: judgements of accident frequency and precautionary intent. J. Safety Res. 24:97-106; 1993. Wood, P. G. A large scale study by interview and observation of exposure to the risk of accidental child poisoning involving household products. Institute for Consumer Ergonomics, Loughborough; 1976. Wood, P. G.; Saunders, A. Product selection for some small-scale studies comparing techniques of measuring exposure to risk. Institute of Consumer Ergonomics, Loughborough; 1976.
Pergamon
RISK OF INJURY PER HOUR OF EXPOSURE CONSUMER PRODUCTS
TO
GORDON HAYWARD Consumer Safety Unit, Department of Trade and Industry, London SWlE 6SW, U.K. (Received
5 August 1993; accepted 15 June 1995)
Ah&act-The aim of this study was to determine and compare the risk of injury per hour of use for a range of consumer products. Exposure data was derived from interviewing a large sample of adults about their use of 76 common kitchen, do-it-yourself and household products. This was combined with hospital sample data for injuries involving each product, to yield the risk-of-injury-per-hour-of-use. Powered cutting equipment, access equipment (ladders and scaffolding) and products with sharp blades were shown to have a comparatively high risk, along with cycles, sunbeds, creosote, cement, car jacks and exercise weights. Perceived risk was shown to be a poor basis for priority setting, but a practical guide to priority for preventive action can be provided by “mapping” products on a plot of the risk of injury per hour of use vs the total medical costs of such accidents. Keywords-Risk, Exposure, Consumer products, Tools, Perceived risk, Medical costs, Home accidents, HASS, Priority setting, Incapacity time
Nor is there a generally accepted and easily determined parameter of injury severity combining fatal and non-fatal injuries. The measure of injury used in this study was therefore the number of patients treated at hospitals irrespective of severity, and the measure of cost was the cost of their medical treatment. The crudest measure of exposure that could be used is simply elapsed time (for example, the probability of injury from a particular cause during one year), but generally a person is only exposed to a particular hazard in a particular environment or when engaged in a particular activity. Deriving measures of exposure for domestic life is much more difficult than for the transport and industrial spheres of activity, because tasks may be performed simultaneously, without discrete points in time when one begins or ends (Wood 1976). The total duration of usage of a product during a year was selected as the most appropriate unit of exposure for this study, since most of the products chosen posed a minimal hazard when not in use. This measure is not universally applicable to all types of consumer products and domestic articles (Wood and Saunders 1976), but it was considered to be the most widely applicable for many of the products most frequently involved in accidents to adults. (The study had to be limited to adults because children switch their attention from one article to another so quickly and frequently that it would not be possible to obtain reliable assessments of their frequency or duration of
INTRODUCTION Individuals, societies and (in particular) governments can face choices between a large number of advocated actions to remove or reduce particular hazards, so it is necessary to have some means of prioritizing the hazards for which action is to be considered. The overall costs (medical and social) of injuries are legitimate concerns in making decisions about the safety of consumer products, but they take no account of the danger posed to the individual by a particular item or activity. However, neither the concepts nor the methodology of risk assessment used in other fields are altogether appropriate for the policy area of consumer product safety, so little account has been taken, to date, of the relative risk of injury, other than by intuition. This study aimed (1) to determine and compare the risks of a range of common consumer products used in the home and leisure sphere, and (2) to combine this risk data with estimates of the costs of accidents involving the products to produce an aid for making priority decisions about safety initiatives.
METHODOLOGY Scientifically, the risk of injury is quantified as a measure of injury divided by a measure of exposure to the possibility of injury. For accidents involving most types of consumer product, there simply are not enough fatalities to furnish a reliable measure of risk. 115
116
G. HAYWARD
use of products from interviews with either them or their parents.) 76 consumer products (mainly kitchen or do-ityourself (DIY) tools and household appliances) were chosen to be studied. These were known from the available accident data (see below) to be involved in a considerable number of accidents to adults in the home and leisure sphere. The overall measure of risk adopted for this study was thus the number of hospital-treated injuries per hour that the product was in use (number-ofinjuries-per-hour-of-use). The questions necessary to calculate mean hours of usage were included in the General Omnibus Survey operated by Research Surveys of Great Britain Ltd during February 1989. Sampling was based on two sets of 136 randomly selected sampling points throughout Great Britain. This produced a representative sample of males and females (each from separate households) aged over 16, who were individually interviewed face-to-face in their homes. For each product in turn, respondents were asked how many were owned, hired or borrowed in the household. If at least one was available, respondents were asked how often they themselves used (any of) this particular product, and then how long they used it for on the most recent occasion, “from getting it out to putting it back”. Respondents were asked to pick the answers to these crucial questions from lists on two cards, which gave ranges of frequency and duration in increasing orders of magnitude. In order to obtain reasonable data on the use of each product, and to limit the effort required by respondents, the sample size was varied from 1000 to 4000, according to how widespread each product was thought to be. (Each sub-sample of 1000 was weighted to correct for sampling deviation from the age, sex and social class profile of the population, prior to analysis). In all 7665 adults (53% female, 15% aged under 25, 17% aged over 65) were each asked about a total of up to 30 products, comprising a mixture of common and uncommon (Research Surveys of Great Britain 1989). In addition, respondents were asked to say how dangerous they felt each product was for an adult to use, on a scale of “very dangerous”/“quite dangerous”/“not very dangerous”/“not at all dangerous”. An earlier pilot study (King 1987) had compared this question wording with four other constructs relating to different aspects of the perception of risk of domestic products: how careful they thought they themselves would need to be to avoid having an accident when using the product; how serious the injury might be if they did have an accident; the type of treatment that might be required; and how many
domestic accidents involving each product they thought would occur to adults. The rankings of the products based on each of the five constructs were highly correlated, with perceived danger giving the same ranking as the combination of all five measures. A high correlation between perceived severity of injury and judgements of “precautionary care” required has also been demonstrated elsewhere (Wogalter et al. 1993). The omnibus survey would not have been large enough to provide reliable injury data for the risk calculations for individual products. Instead, injury rates per adult per year from accidents involving these products (excluding occupational and motor vehicle accidents) were derived from the existing hospital-based sample of the Home and Leisure Accident Surveillance Systems-HASS and LASS-which record information from patients attending the accident and emergency departments of a sample of 22 hospitals (only 11 for LASS) representative of the United Kingdom (Department of Trade and Industry 1990). The annual exposure of each respondent to a product in their household was calculated by multiplying the number of occasions per year on which they used the product by how long they used the product on the last occasion. The mean annual exposure figure for all adults in households possessing the product was then calculated, and multiplied by the proportion of households owning the product to give the mean exposure per adult member of the population. (Note that this is not a very meaningful parameter of exposure in itself, but it converts the exposure and injury figures to a common population base.) Estimates of numbers of accidents treated in hospitals per adult member of the population were calculated from the HASS and LASS data for all injuries to adults involving the products under study. (Corrections were made for cases where details such as the power source of the product were not recorded.) The risk of an accident per hour of exposure was finally obtained by dividing the frequency of accidents per adult by the number of hours exposure per year per adult for each product. The responses to the question of how dangerous each product was thought to be were scaled from 1 (not at all dangerous) to 4 (very dangerous). The mean score for each product was calculated to give a surrogate measure of perceived risk. The HASS database has a facility for estimating the duration of incapacity and the medical costs of each case. The calculations take into account the age of the patient, the part of body injured, the type of injury and the length of any period of hospitalization.
Injury risk of exposure to consumer products
This facility was used to derive mean figures for the incapacity and medical cost of accidents involving each of the products in turn. The mean costs were then multiplied by the figures derived above for the number of accidents per adult member of the population involving each product. It was not possible to calculate the social costs of the accidents. To obtain a measure of the distribution of risk, both hours of exposure and numbers of accidents were summed cumulatively across all the products and the “complementarity point” on the “Lorenz curve” (Finkel 1990) obtained. RESULTS The Table shows the products listed in descending order of risk. 79.7% of the accidents involved products that were associated with only 20.3% of the exposure, but it should be remembered that this was a set of products selected because they were known to be involved reasonably often in domestic accidents. For the entire population of consumer products a much higher degree of concentration would be expected. When looking at products displaying the highest risk, it should be remembered that this is not a comprehensive list of consumer products, nor necessarily of those with the highest risk of an accident, and that these findings are of course generalizations and do not necessarily apply to individual models. Nevertheless, it is worth noting that where the risk of an accident is greater than S/million hours, certain groups of products feature most frequently, (1) powered cutting equipment (particularly electrically powered); (2) access equipment (ladders and scaffolding); and (3) sharp blades-knives, saws, chisels and axes (accidents involving knife sharpeners also belong to this group). However, there are also some miscellaneous articles-cycles, sun beds, welding equipment, creosote, cement, training weights and car jacks. There are a number of interesting comparisons between the risk of an accident for similar products using different power sources, for example hedge trimmers (petrol and electric), welding equipment (electric and gas), saws (electric and hand), carving knives (electric and hand), drill braces (electric and hand) and ovens or hobs (electric and gas). Among the products associated with the longest mean duration of incapacity, one group is very prominent-ladders and scaffolding. This is probably because, like baths, they are often involved in serious falls causing fractures or head injuries which are likely to require hospitalization. The Table shows the total medical cost per adult in the population per year, not the cost per case.
117
Note that bicycles are the product group associated with the highest medical costs even though this study excludes road traffic accidents (i.e. where a bicycle was in collision with a moving motor vehicle). Accidents to adults involving bicycles cost about g3.7 million worth of medical resources for the United Kingdom as a whole in mid-1980s prices. Ladders and baths also rank highly on total medical costs, having both a high frequency of involvement in accidents and being associated with a long duration of incapacity. The high ranking of craft and carving knives, however, is entirely due to the frequency of accidents involving them, the mean incapacity time being very low. Figure 1 shows that there is only the vaguest of relationships between the number of accidents per head of population and the risk to an individual (correlation coefficient = 0.18), and that the measured risk may be ten times more or less than what would be predicted from assuming a direct relationship to accident rate. For example, accident rates overemphasize the danger of cycles, baths, scissors, ovens, irons, and hot water bottles, while under emphasizing that of scaffolding, chainsaws, creosote, hedge-trimmers and welding equipment. Figure 2 shows that the ranking that adults themselves gave to the relative risk of products was also a rather poor guide to their actual risk of injury (correlation coefficient = 0.47). For example, respondents overestimated the relative risk of blowlamps, chainsaws, electric blankets, scalpels and hand braces, while underestimating the risks of bicycles, wheelbarrows, brushes, cement and baths. DISCUSSION People’s perception of comparative danger of products is clearly an unreliable guide to the actual risk of injury of a product in use. Consideration of which products tend to be over-rated in terms of hazard and those which are under-rated, suggests that people rely over-much on constructs of sharpness and power of products in their perception of danger, rather than on an assessment of the situations that can arise during use of the products, and the likelihood of them doing so. Furthermore, it has been shown elsewhere (Wogalter et al. 1993) that even prompting respondents to analyse accident scenarios does not influence their ranking of products by perceived risk. The need for objective criteria for priority setting is therefore clear. Currently, if any scientific data is used at all as an aid to deciding which consumer product hazards should receive priority attention, the parameters considered are either the number of injuries (fatal or non-
118
G.
Table 1. Exposure,
Product
name
Electric hedge-trimmer Scaffolding _ Electric welding equipment Food slicer Chopper or axe Craft or DIY knife Bicycle Creosote(wood preservative) Sunlamp or heatlamp Electric circular saw Electric grinder/mill Ladder for leanmg Stepladder/household ladder Electric planer Sunbed or solarium Weight-training weights Knife sharpener Car jack Manual carving knife Electric chainsaw Hammer or mallet Chisel Cement powder/wet morter Petrol lawn mower Petrol-driven chainsaw Handsaw Electric carving knife Loft(attic) ladder Scalpel Saucepan(stove-top pot) Gas welding equipment Glue or adhesiieElectric drill I brace) Petrol hedge’trimmer Electric lawn-mower Chip pan/deep fat fryer Razor for wet shaving Garden fork Bath Sewing needle Hand-powered plane Garden shears Electric nylon line trimmer Secateurs (pruning shears) Shower Screwdriver Hand-powered lawn-mower Exercise equipment Wheelbarrow Electric sewing machine Barbeque Spanner(wrench) Manual sewing machine Scissors Deckchair/sun lounger Pliers Tin opener Gas blowtorch or blowlamp Grater/peeler Broom/brush Garden rake or hoe Frying pan Pressure cooker Microwave oven Electric iron
Total accidents (per million persons per year) 83 49 47 29 82 458 699 14 54 46 31 228 379 26 21 111 16 47 217 12 283 106 36 38 7 99 22 30 16 55 6 36 67 2 74 83 49 62 250 88 7 24 10 41 75 98 19 29 30 22 6 48 4 83 44 10 17 3 12 28 16 24 8 21 41
HAYWARD
risk and injury costs of consumer
products
Total exposure (hours of use per person per year)
Risk (accidents per million hours of use)
Perceived risk (rating of l-4)
1 1 1 1 4 22 35 1 4 3 2 19 37 3 2 11 2 5 26 1 39 15 5 6 1 16 5 6 3 13 1 9 19 1 22 26 16 22 93 34 3 10 4 17 33 46 9 17 17 15 5 39 4 76 48 12 21 5 20 47 28 49 19 58 117
104 65 37 23 21 21 20 19 15 15 13 12 10 10 10 10 10 9 8 8 7 7 7 6 6 6 5 5 5 4 4 4 4 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 1 1 1 I 1 1 1 1 1 1 1 1 .5 .4 .4 .4
3.3 3.0 3.2 2.7 3.1 2.8 2.0 2.4 2.7 3.6 2.9 2.6 2.4 2.8 2.6 2.2 2.2 2.6 2.7 3.7 2.0 2.6 1.8 2.6 3.7 2.4 3.0 2.0 3.3 2.5 3.4 2.5 2.6 3.2 2.6 3.0 2.1 2.0 1.7 1.9 2.2 2.2 2.7 2.1 1.6 1.9 2.1 1.8 1.2 1.8 2.4 1.5 1.8 2.2 1.5 1.5 1.6 3.3 1.7 1.2 1.6 2.4 2.3 1.9 2.2
Mean incapacity (per accident)
Total medical cost (per million persons per year)
Cdwl
CUW
6.7 18.0 8.6 5.5 8.0 5.7 13.3 9.6 9.5 9.3 6.7 18.8 19.7 6.8 10.1 13.6 5.0 13.8 4.9 7.0 13.4 6.6 14.0 11.0 9.5 5.4 5.2 16.7 5.1 11.4 9.1 9.8 8.7 9.0 12.1 11.1 7.0 10.0 19.4 6.2 7.6 9.3 9.0 7.8 15.4 7.0 13.2 14.3 15.6 7.8 10.8 8.7 8.5 6.6 15.1 10.1 5.8 11.1 4.2 13.3 13.9 10.9 9.7 12.1 12.2
5343 9546 3708 1062 4455 18943 81270 1097 3312 7933 1593 36786 53353 1313 1208 10054 566 4000 8444 527 21145 5192 2698 4476 603 4158 1164 4226 606 3840 296 2988 5556 123 9754 5546 2211 3475 34321 5080 385 1427 525 1942 8315 5139 2035 1341 2868 1037 365 2991 220 3816 3926 535 684 208 408 3160 1691 1562 600 1460 2730 -continued
opposite
Injury risk of exposure to consumer products
119
Table 1. (continued) Total accidents (per million persons per year)
Product name Work bench Hair drier Gas oven Cigarette lighter Electric hob(stove-top) Electric oven Hand-powered drill( brace) Gas hob(stove-top) Knitting needle Hot water bottle Electric blanket
11 11 46 7 31 31 3 24 14 21 6
Total exposure (hours of use per person per year)
Risk (accidents per million hours of use)
35 35 155 33 141 157 17 169 116 239 129
fatal) or their consequent cost to the economy. There may be some justification for this in fields where the preventive actions will be paid for from taxes, but safety improvements to a consumer product will inevitably be paid for through increased prices to the consumers of the particular product, not society as a whole. Attempts to rank products in order of priority based on total accidents or total costs are also highly dependent on how each product category is defined. For example, gas ovens and hobs are frequently (though not universally) manufactured as one product-a gas cooker (stove), but treating them as one
.3 .3 .3 .2 .2 .2 .2 .l .1 .I .O
Perceived risk (rating
Mean incapacity (per accident)
1”:)
[days1
1.5 1.7 2.2 2.2 2.2 1.9 2.5 2.3 1.8 1.8 2.5
16.4 15.5 13.5 9.9 11.2 13.7 7.5 14.4 7.7 13.6 16.3
Total medical cost (per million persons per year)
CUW 924 1117 7334 477 2237 2265 156 5755 624 2302 1552
product category would raise their ranking in terms of total medical costs from 13th to 7th place. This is an inherent problem in trying to use accident cost (or just frequency) to rank consumer products in terms of priority for preventive action. Furthermore, as this study has shown, the number of accidents involving each product is not a good guide to its comparative risk, and leads to a different ordering of priorities, focusing on more common products. Rationally, therefore, the risk of injury to the product user should be considered as at least an important factor, if not the prime one. The study has
1000
100
10 Eke
blanket
1
c]
L
0.01
0.1
1
10
Accident risk per million hours of exposure Fig. 1. Accident rate per year vs accident risk per hour of exposure for consumer products.
100
G. HAYWARD
120
Very
Quite
Not very
Not L at all 0.01
Accident Fig. 2. Perceived
risk vs calculated
risk per million
hours of exposure
risk per hour of exposure
for consumer
products.
100,000
1000
100
Accident Fig. 3. Medical
10
1
0.1
0.01
cost of accidents
risk per million
vs risk of accident
100
hours of exposure
per hour of exposure
for consumer
products.
Injury
risk of exposure
shown that it is possible, for adults, to obtain data for number-of-injuries-per-hour-of-use from a corn@ nation of injury data from a sample of hospitals and exposure data from a large scale household survey. However, the economic cost of injuries cannot be ignored, so overall, the allocation of priorities for preventive action can best be guided by considering the comparative positions of particular products on a plot such as Fig. 3. This shows the risk of an accident to the population against the total cost to an individual using a product of such accidents. What is of interest here is not the lack of relationship (correlation coefficient = 0.15) between the parameters, but the way the Figure provides a twodimensional map as an aid to deciding priorities for action. It is clear that action to prevent accidents involving the products at the top right corner would be highly desirable (if effective actions could be devised) since currently both the risk of an accident and the consumption of medical resources is high. There is no cut off point for including products in such a priority list, but their relative importance decreases towards the bottom left hand corner of the figure. Figure 3 does not, of course, show more than an
important fraction of the consumer products available, but there is a broad range of consumer products
to consumer
products
121
against which others can be compared (assuming accident risk and medical costs can be estimated for them), to provide more appropriate guidance to policy makers.
REFERENCES Department of Trade and Industry. Twelfth annual report of the Home Accident Surveillance System-1988 data. London: DTI; 1990. Finkel, A. M. A simple formula for calculating the “mass density” of a lognormally distributed characteristic: applications to risk analysis. Risk Anal. 10(2):291-301; 1990. King, Y. Risk: exposure and perception pilot study. Internal report, Consumer Safety Unit; 1987. Research Surveys of Great Britain. Omnibus consumer products risk exposure study. Unpublished report to Department of Trade and Industry; 1989. Wogalter, M. S. et al. Risk perception of common consumer products: judgements of accident frequency and precautionary intent. J. Safety Res. 24:97-106; 1993. Wood, P. G. A large scale study by interview and observation of exposure to the risk of accidental child poisoning involving household products. Institute for Consumer Ergonomics, Loughborough; 1976. Wood, P. G.; Saunders, A. Product selection for some small-scale studies comparing techniques of measuring exposure to risk. Institute of Consumer Ergonomics, Loughborough; 1976.