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Public Health Focus: Effectiveness of Rollover Protective Structures for Preventing Injuries Associated with Agricultural Tractors

Agriculture ranks fourth among U.S. industries for work-related fatalities (1). Fatalities associated with agricultural machinery commonly involve farm tractors, and rollover incidents (i.e., the tractor tips sideways or backward and overturns, crushing the operator) account for 46% (Minnesota) to 76% (Georgia) of all farm tractor-related fatalities (2). Annually, agricultural tractor rollovers result in approximately 132 work-related deaths among persons aged greater than or equal to 16 years * (3). This report summarizes in- formation regarding the efficacy, effectiveness, and cost-effectiveness of rollover protective structures (ROPS) on agricultural tractors. Background

ROPS are structural components attached to vehicles and are designed to protect the operator if the vehicle overturns during operation; they can either be enclosed in a tractor cab or unenclosed (resembling one or more exposed rollover bars). Safety restraints should be used in conjunction with ROPS to confine the operator within the space protected by the ROPS. ROPS first became available as optional equipment on farm tractors in 1971; tractors manufactured before 1971 generally were not designed to accommodate the addition of ROPS. In 1976, the Occupational Safety and Health Administration (OSHA) required employers to provide ROPS and safety belts for all employee-operated tractors manufactured after October 25, 1976. ** Since 1985, as a result of voluntary agreements by tractor manufacturers, virtually all new tractors sold in the United States have been equipped with ROPS and safety belts.

More than half of the approximately 4.6 million tractors in use in the United States lack ROPS; of these, 61% were manufactured before 1971 (NIOSH, unpublished data, 1992). In an eight-state (Delaware, Illinois, Indiana, Missouri, New York, Ohio, Oregon, and West Virginia) survey covering approximately 14,000 tractors, 65% of tractors had no rollover protection, 27% had enclosed ROPS, and 8% had unenclosed ROPS (NIOSH, unpublished data, 1992). When analyzed by time in use, 54% of total tractor hours of use was performed with no rollover protection, 36% with enclosed ROPS, and 10% with unenclosed ROPS. Efficacy and Effectiveness

Since 1967, a series of tractor rollover incidents has been investigated in Nebraska (R. Schneider, University of Nebraska, personal communication, April 1992); 40% of approximately 250 persons involved in unprotected tractor rollover incidents died. One (2%) of 61 persons operating ROPS-equipped tractors that rolled over died; this person had not used a safety belt and was ejected from the ROPS protective zone during the rollover.

Based on the calculation of a prevented fraction (4), NIOSH estimated that 43% of potential fatalities from rollovers are prevented by the enclosed and unenclosed ROPS now in use. Based on the attributable risk calculation (4), NIOSH estimated that a 71% reduction from the current number of rollover fatalities would be expected by increasing the use of unenclosed ROPS to cover all tractors that do not already have any form of ROPS.

Assumptions used to estimate values for these measures were that 1) no rollover-associated deaths occur in tractors with enclosed ROPS; 2) currently 10% of all tractor-hours are logged by unenclosed ROPS-equipped tractors; and 3) the fatality rate per hour of use in tractors with unenclosed ROPS is 75% less than the corresponding rate in tractors without any ROPS. There are no epidemiologic studies doc- umenting the efficacy of unenclosed ROPS; based on current knowledge, 75% was selected for this analysis as a reasonable estimate (5). All estimates were made for retrofitting tractors with unenclosed ROPS because this approach would be less expensive and technically simpler than retrofitting tractors with enclosed ROPS. Cost-Effectiveness

A cost-effectiveness analysis reported in 1991 assessed a hypothetical statewide policy to retrofit ROPS onto tractors in New York. The policy involved 1) monetary incentives to retrofit tractors for 5 years, 2) mandatory ROPS on all tractors after 10 years, and 3) enforcement of the proposed policy (5). With the assumptions that retrofitted ROPS would be 75% efficacious and that ROPS installation costs $700 per tractor, the minimum cost (based only on ROPS installation {i.e., hardware and labor}) for each life saved was estimated as $684,729. Enforcement (per million dollars of enforcement expenses) of such a program would cost an additional $337,672 per life saved. Reported by: Div of Safety Research, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: Rollover-associated fatalities and serious traumatic injuries to operators of tractors without ROPS can be substantially reduced through 1) retrofitting tractors manufactured from 1971 through 1985, for which ROPS equipment is available, and 2) refurbishing and retrofitting pre-1971 tractors, for which ROPS designs generally do not exist. If all tractors without ROPS are left unprotected, 2800 rollover-related deaths may occur during the approximately 31 years *** until these tractors have been gradually retired from use (based on current fatality rates per 100,000 tractors in use {7} and the recognized underreporting of this type of fatality).

In the United States, the annual fatality rate related to farm tractor operation declined from 14.9 fatalities per 100,000 tractors in use in 1970 to 7.2 per 100,000 tractors in use in 1989 (8). This decline may have resulted from a combination of compliance with the OSHA standard and the voluntary use of ROPS on tractors (8).

The findings in this report suggest that the potential public health benefit of retrofitting ROPS on tractors could be substantial -- ranging up to a 71% reduction from current fatality numbers. However, if the efficacy of unenclosed ROPS were higher than the 75% used in these analyses, these estimates of positive public health impact would increase; the efficacy of ROPS would approach 100% if accompanied by universal use of safety belts or other driver restraints (e.g. restraint bars) on unenclosed ROPS-equipped tractors. Retrofitting tractors with enclosed ROPS, although substantially more costly, would also be expected to prevent more deaths because operators are more likely to remain within the cab during a rollover and, therefore, be at decreased risk for being crushed -- even if they are not wearing a safety belt. From 1961 through 1983, Sweden implemented regulations requiring the installation of ROPS -- initially on new tractors, then on all tractors; this intervention was followed by a 92% reduction in tractor rollover fatalities (9). Although other factors (e.g., improvements in tractor stability, operating techniques, safety precautions, and medical care of injuries) may have contributed to this decline, the ROPS regulations likely contributed substantially to this trend.

One of the national health objectives for the year 2000 is to reduce the fatality rate for persons who work on farms from 14.0 deaths per 100,000 workers (1983-1987 average) to 9.5 deaths per 100,000 workers (10). National and community-based injury-prevention programs should include plans for retrofitting or refurbishing farm tractors with ROPS to prevent fatalities associated with tractor rollovers. These programs may include 1) a buy-back of older, less safe tractors; 2) interventions tailored to the needs of specific farming regions (e.g., dairy, grain, and orchard); and 3) effectiveness studies of community- and demonstration-project intervention initiatives (4). In addition, guidelines should be developed for design of ROPS for tractors manufactured before 1971.


  1. Bell C, Stout N, Bender T, Conroy C, Crouse W, Myers J. Fatal

occupational injuries in the United States, 1980 through 1985. JAMA 1990;263:3047-50.

2. Purschwitz M, Field W. Scope and magnitude of injuries in the agricultural workplace. Am J Ind Med 1990;18:179-92.

3. Etherton J, Myers J, Jensen R, Russell J, Braddee R. Agricultural machine related deaths. Am J Public Health 1991;81:766-8.

4. Kleinbaum DG, Kupper LL, Morganstern H. Epidemiologic research: principles and quantitative methods. New York: Van Nostrand Reinhold Company, 1982.

5. Kelsey TW, Jenkins PL. Farm tractors and mandatory roll-over protection retrofits: potential costs of the policy in New York. Am J Public Health 1991;81:921-3.

6. Wilson M. New tractor trauma. Prairie Farmer, January 1993:26- 7.

7. National Safety Council. Accident facts, 1990. Chicago: National Safety Council, 1990.

8. Murphy DJ. Trends in twenty years of tractor accident statistics. St. Joseph, Michigan: American Society of Agricultural Engineers, 1990; paper no. 90-1639.

9. Springfeldt B, Thorsen J. Mitigation of personal injuries caused by overturning of farming tractors. In: Proceedings of the 31st Annual Conference of the American Association for Automotive Medicine. Washington, DC: National Center for Statistics and Analysis, 1987:229-36. 10. Public Health Service. Healthy people 2000: national health promotion and disease prevention objectives -- full report, with commentary. Washington, DC: US Department of Health and Human Services, Public Health Service, 1991; DHHS publication no. (PHS)91-50212.

  • This is an undercount of tractor rollover-related fatalities

because persons aged <16 years are not included in the database used to derive this figure; it is also likely that additional fatalities occur among persons aged>16 years but are not reported as work-related.

** This OSHA standard (CFR 29 section 1928.51) exempts tractors used in certain circumstances (e.g., where vertical clearances may be limited, such as in orchards or inside buildings) and does not apply to family farms. Moreover, the standard is not enforced on farms that employ fewer than 11 employees. *** Estimated from total number of tractors in use divided by annual sales rate (6).

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