Mechanization and risk of occupational accidents in the logging industry

Journal of Occupational

10 (1988) 191-198 B.V., Amsterdam - Printed

191

Accidents,

Elsevier Science Publishers

in The Netherlands

Mechanization and Risk of Occupational Accidents in the Logging Industry* LUCIE LAFLAMME

and ESTHER

CLOUTIER

Institut de Recherche en Sank! et en SdcuritR du Travail du Qukbec (IRSST), 505 Boul. de Maisonneuue Ouest, Montrdal, Qudbec H3A 3C2 (Canada)

(Received 25 February 1988; accepted 11 July 1988)

ABSTRACT Laflamme, L. and Cloutier, E., 1988. Mechanization and risk of occupational logging industry. Journal of Occupational Accidents, 10: 191-198.

accidents

in the

The decrease in frequency of occupational accidents in the logging industry is a positive outcome of mechanization of delimbing and debranching activities. Furthermore, the variance in the number of accidents on mechanized sites as opposed to conventional ones, cannot be satisfyingly explained by fluctuations in the volume of production or by the number of workers exposed. The relative risk of accidents, estimated using the total number of accidents and the total number of workers exposed, is significantly different from one occupation to another. It is lower in occupations where machinery and equipment serve as substitutes for human strength and physical effort. In these latter occupations, workers are hurt while performing maintenance and repair tasks rather than during direct production ones. These results support the hypothesis that an improvement in technology reduces the risk of occupational accidents. They also suggest that preventive measures for technologically improved occupations and processes have to take into account the possible appearance of new dangerous tasks and situations.

INTRODUCTION

This paper analyzes the relationship between the mechanization of delimbing and debranching activities in the logging industry and the frequency of occupational accidents. The mechanized cutting process eliminates the use of power saws on logging sites, and diminishes considerably the necessity for human physical effort during most production-related tasks. Lastly, protection from environmental hazards during production is provided by the design of the machines. Such changes should lead to a significantly lower accident rate. The literature includes very few studies dealing with technological change *Reprint requests should be addressed to: Ms. L. Laflamme, Ouest, Montreal, Quebec, Canada H3A 3C2.

0376-6349/88/$03.50

IRSST, 505 Boul. de Maisonneuve

0 1988 Elsevier Science Publishers

B.V.

192

and the variation in accident risk. Saari (1976/77) observed a decrease in accidents when analyzing a country’s general and retrospective tendencies over a few decades; he suggested that this decrease could be explained in part by technological changes in different economical activity sectors. Kersten and Ulrich (1976) compared accident frequency rates in three firms before and after mechanization or automation. This survey showed contradictory results: after the changes, accident rates diminished in two firms and increased in the third one. Other researchers studied risks in highly mechanized work stations or occupations and found that relative risk was higher in maintenance and repair tasks, as compared to immediate production ones (Vautrin and Dei Svaldi, 1985; Vayrynen, 1982; Saari, 1982). Mechanized production tasks mostly require control intervention from workers when they are carried out, thus reducing physical efforts. In our study, we compared accident frequencies on mechanized and conventional logging sites. An analysis of the variance in the number of accidents was carried out using the number of workers exposed and the volume of production as predictors, and the cutting process as grouping variable. The relative risk of accidents within cutting processes and occupations with reference to their particular technological advancement has been calculated and compared. Those comparisons covered four different occupations: fellers, skidder operators, delimber operators and debrancher operators*. It should be emphasized, however, that the characteristics of occupations are different after mechanization. In conventional cutting with power saws, fellers are responsible for cutting and debranching trees which will be later removed from the logging sites and piled near the roads by skidder operators. The main tasks of skidder operators, both in conventional and mechanized cutting, consist of manually chaining delimbed trees to skidder cables, removing them from the logging site with the skidder, and manually unchaining them and piling them up. In mechanized cutting, the delimbing and debranching tasks are separated and carried out by machines with an articulated arm. Operators perform their respective assignments by manipulating controls inside a cabin. MATERIAL

AND METHODS

Two companies participated in the survey. On were compiled for a period extending from January tion and occupational accident registers for the 8 companies were used. Accident registers included

a retrospective basis, data 1981 to July 1984. Produclogging sites owned by the all 358 occupational acci-

*The results of this survey are included in a doctoral thesis accepted by the Graduate School of the UniversitC Laval. The thesis director was Alain Vinet of the Department of Industrial Relations (Laflamme,

1987).

193

dents that occurred over these three and a half years and that were reported by workers to their company representatives. For each accident, the registers also indicated the site where it took place, the time of occurrence (hour and date) and the occupation of the injured worker. Production registers for each site included the production volume, the number of workers employed, and the cutting process used on each site throughout this period. Because of inconsistencies in the registering of production volume, a month was chosen as the unit of observation for analytical purposes. In the analysis of variance, the depent variable was the total number of accidents on a site during a month; the two independent variables were the total volume of wood produced and the number of workers employed during the same month. Regression curves for the mechanized and the conventional sites were compared (Zehna, 1970). When the number of workers employed varied from one week to another, the average number of workers over the four weeks of the month was used. The total number of months was 289: 177 in mechanized operations, and 112 in conventional. To establish relative risk, the average number of accidents per worker in each subgroup was calculated using the total number of accidents as numerator and the total number of workers exposed as denominator. All 358 accidents were classified according to cutting process and occupation. The total number of workers exposed in each cutting process was calculated by using the annual average number of workers on each site and by summing up annual data for the 8 sites studied. Since no precise occupational data were accessible in any production of payroll register, each occupation’s denominator was estimated by the companies who specified, for each logging site, the proportion of workers assigned to each occupation every year. A T test was used to compare the resulting means in the two-by-two comparisons (Zehna, 1970). RESULTS

Correlation matrices obtained from the analysis of variance are shown in Table 1. This table indicates that the correlation between monthly production volume and the number of workers is high both in conventional and mechanized operations. When conventional and mechanized processes are grouped, the average number of workers has a greater correlation with the total number of accidents, than with the total volume of production. In mechanized cutting, in contrast to conventional cutting, the total number of accidents is slightly correlated to the number of workers as well as to the volume of production. Moreover, R” given in Table 2 confirms that the combination of the total volume of production (nl ) and the average number of workers exposed (+x2) is a strong and positive predictor of the number of each of accidents (y) in conventional operations (R2=0.64) and a useless one in mechanized processes (R”=0.02). Table 2 also presents equations for the regression curves for the

194 TABLE

1

Correlation

matrices

between

production,

Variable (per month)

and accidents

Total

number

volume of workers of accidents

1

2

1 0.56

1

0.41

0.73

3

1

Correlation between the number of workers and accidents, and accidents, are both very high in conventional cutting ventional

portrait

influences

the results

for each cutting

Conventional (n=112)

(n=289)

1. Total production 2. Average number 3. Total

workers

obtained

when

process

Mechanized (n=177)

1

2

?J

1 0.70

1

0.70

0.77

1

1

2

1 0.79

1

0.15

0.01

3

1

as well as between volume of production but very poor in mechanized. The conthe two cutting

processes

are grouped.

two cutting processes when the number of accidents (y) is predicted by the production volume in a month (x, ) and the number of exposed workers (.x2 ). The difference between these t,wo regression curves is highly significant (F=31.33;p
2

Prediction

of the number

of accidents

(obtained

using

the production

volume

and t,he number

01

workers) Cutting

process

Conventional Mechanized

Multiple r

R’

F:quation,’

0.80 0.15

0.64 0.02

3’= -0.81+0.32x, .I’= 0.2610.18x,

+0.55x, -0.04X,

‘F=:31.:I:i:p< 10 ;. J’= Number of accidents; K, = Production volume; and .Y?= Number of workers. There is a highly significant difference between mechanized and conventional cutting when considering the accident variance as predicted by production volume and number of workers exposed.

195

TABLE 3 Occupational

accident incidence

Groups compared

rates for each occupation

Comparison proportions

Number of

between

Occupational accidents

Workers exposed

Rate

T

278

1058 908 1966

0.26 0.09 0.18

8.50

< 0.05

525 516 1041

0.35 0.17 0.26

6.66

< 0.05

364 232 263 859

0.13 0.03 0.06 0.08

4.44”

< 0.05

Cutting processes Conventional Mechanized Total

80 358

Conventional cutting Feller Skidder operator Total

88 274

Mechanized cutting Skidder operator Delimber operator Debrancher operator Total

and cutting process

186

49 8

- 16 73

P

,‘There is no significant difference between delimber and debrancher operators (T= 1.57). These two occupations were grouped in order to compare them to the skidder operator. The occupational accident incidence rate in conventional cutting is significantly higher than the one in mechanized cutting. This rate is also more significant for delimber operators than for skidder operators in conventional cutting, and for skidder operators compared to delimber and debrancher operators together in mechanized cutting. DISCUSSION

Prediction

of accident frequency

The total number of workers employed on a logging site is positively correlated to the total volume of production in a month for both conventional and mechanized operations. However, the mechanization of delimbing and debranching tasks on logging sites is a technological improvement that modifies the organization and achievement of production in such a way that a site’s accident rate can no longer be predicted using parameters that were welladapted to conventional processes. For the latter processes, an increase in the number of accidents can be expected where there is an increase in the number of workers and/or in the production volume. On mechanized sites, this assumption is not valid. In other words, the occurrence of occupational accidents in technologically

196

improved processes does not greatly depend on product,ion activities, as measured in our survey. This occurrence would be related to activities other than immediate production ones, as suggest,ed by Vautrin and Dei Svaldi (1985) and Vayrynen (1982). In fact, technological improvement such as mechanization in the forestry sector might effectively tend to reduce exposure to accident risk during production activities. During production, workers are physically protected from environmental hazards and they control rather than perform the tasks for which t,he new machines are designed. It is when production stops for maintenance or repair, that, workers are more directly exposed to different hazards. Moreover. maint,enance and repair tasks are less fre~~lent and are generally less time consuming than production ones. On this sultject , it has already been indicat,ed elsewhere (Cloutier and Laflamme. 1985; Iaflamme et al., 1985; Laflamme, 1987) t,hat the small number of’ accidents recorded by delimber and debrancher operators mainly occurred during maintenance and repair activities or while moving machinery on the sites. Logger and skidder operators also hurt themselves during displacements on sites, but have a higher percentage of accidents while performing their respective production assignments. Hence, risk exposure on mechanized sites appears to shift from immediate production tasks to other tasks which are rather somewhat secondary or rclated to product ion and which take place over shorter lengths of time. To sat; isfactorily predict the variance in the number of accidents for mechanized operations, it might be preferable to use indicators of machinery use and of the time spent either to ~naintain or repair machines. Furthermore, the number of machines instead of the number of workers is probably a bett.er predictor of accident variance.

Reduced risk in mechanized activities is confirmed first by conlparing the average individual number of accidents in the two cutting processes. Similar results have also been obtained in two of the three firms analyzed by Kersten and I-lrich ( 1976) bef’ore and after technological improvement. Reduced exposure to risk with mechanization is similarly confirmed by comparing the relat iv-e accident risk within cutting processes. In convent,ional cut ting, fellers working with a power saw record and average number of accidents that is two times higher than that of skidder operators who remove felled trees f’rom logging sites by driving and operating a skidder. However, on mechanized sites, skidder operators face a significantly higher relative risk t,han delimber and debrancher operators. It was explained earlier that in the course of production, skidder operators have to manually chain and unchain skidded trees. They move around their machine many times during a working day and also have t,o exert physical

197

effort every time they chain or unchain trees using a choke. During this process, they are more directly exposed to hazards than delimber and debrancher operators who remain seated in their cabins and control the action and movement of their machine’s articulated arm. Furthermore, these differences in the content and in the nature of the tasks from one occupation to another do not result only in significant differences in the relative risk of accident. They are also reflected in important and equally significant differences in the type of accident and in the circumstances surrounding the accident (Cloutier and Laflamme, 1987). Again, as Saari pointed out ( 1976/77), a finer breakdown between the nature of the tasks or the time required to perform each of them in each occupation might be a more relevant way to describe occupational accident risk. It should finally be mentioned that this study revealed no significant difference in the seriousness of accidents. The average length of absence by accident was in fact comparable between types of cutting, and work stations in each type of cutting (Laflamme, 1987). The very asymmetrical distribution of length of absence by accident for injuries, as well as the low number of accidents recorded by feller and debrancher operators in mechanized cutting, do not allow easy conclusions on this subject. CONCLUSION

The mechanization of delimbing and debranching operations significantly reduces the overall potential risk of accidents on mechanized sites as compared to conventional ones. This technological improvement is sufficiently advanced to have another type of effect on occupational accidents. For delimber and debrancher operators, in contrast to fellers, occupational accident risk is not to a great extent related to production activities. For these workers, almost all the injuries occurred in maintenance and repair activities. Therefore, as production gets safer with technologically advanced machinery, occupational accident risk deminishes and is transferred to tasks that are required to operate this more powerful equipment,. Prevention policies, programs and practices have to follow this risk transfer in order to provide appropriate monitoring and control of safety measures. The secondary effects of technological change will have to be well understood and defined in order to adjust preventive measures on logging sites. A good understanding of the unexpected outcomes of technological advancements might also help designers and manufacturers design machines which would not only be more productive but also easier to maintain.

REFERENCES Cloutier, E. and Laflamme, L., 1985. Organisation du travail et skcuritk des opkrations forestikres. Rapport de recherche 005, IRSST, MontrBal, 487 p.

198 Cloutier, E. and Laflamme, L., 1987. Typologie d’accidents en for&t: Utilisation d’analyse multidimensionelles. Actes du colloque sur l’analyse des don&es et a la securitk du travail. IRSST, Montreal, Janvier 1987, pp. 63-74. Kersten, E. and Ulrich, H., 1976. Resultats dune etude sur la frkquence en relation Z. Gesamte Laflamme, L., operations

de deux techniques appliquee a la Sante’

des accidents

du travail

avec la mkcanisation et l’automatisation graduelles des techniques de production. Hyg. Ihre Grenzgeb., 22(5): 370-373 (traduction INRS 51B-76). Cloutier, E., Blanchard, M. and Arsenault, A., 1985. Mecanisation et securite des forest&es: analyse multidimensionelle des perceptions des travailleurs et des ac-

cidents rapport&. Colloque International Securitd du Travail, AISS, Bonn, R.F.A.,

sur I’Automatisation, pp. 364-379.

les Techniques

Nouvelles

et la

Laflamme, L., 1987. Organisation et securite du travail: Impact quantitatif et qualitatif dun changement technologique. These de Doctorat, Faculte des Sciences Sociales, Universite Laval, Quebec, 285 p. Saari, J., 1976/77. Characteristics of tasks associated with the occurrence of accidents. J. Occup. Accid., 1: 273-279. Saari, J., 1982. Accidents and progress of technology in the Finnish industry. J. Occup. Accid., 4: 133-144. Vautrin, J.P. and Dei Svaldi, D., 1985. Bilan de l’etude des installations robotisees francaises en ce qui concerne les consequences sur l’hygiene et la skcuritk. Deuxieme Colloque du Comitk Recherche de 1’AISS: l’automatisation, les techniques nouvelles et la securite du travail - crit&es et methodes pour l’analyse de la securite. Compte Rendu, Paris, INRS, pp. 158-165. Vayrynen, S., 1982. Occupational accidents in the maintenance of heavy forest machinery. Occup. Accid., 4: 175. Zehna, P., 1970. Probability

Distributions

and Statistics.

Allyn and Bacon

Inc., Boston,

622 p.

J.