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Safeguarding of lathes and occupational accidents
ELSEVIER
Safety Science 21 (1995) 15-22
Safeguarding of lathes and occupational accidents Unto Varonen Labour Protection District of Hiime, Lahti. Finland Tampere Universityof Technology, Tampere. Finland
Accepted ! November 1994
Abstract
The purpose of the study was to determine whether better safeguarding of lathes used for metal cutting had affected the number of occupational accidents occurring during metal lathe work. The study consisted of two parts: (i) safeguarding of lathes and analysis of lathe accidents which occurred throughout the entire province of H~ime; and (ii) safeguarding of lathes and analysis of lathe accidents in 12 target enterprises. The safeguarding of lathes as well as the number and type of lathe accidents were studied from July I, 1981 to June 30, 1982, and again from January 1 to December 31, 1986. The safeguarding of lathes improved during the periods studied, both in the whole province of Hame and in 12 target enterprises. In the province of H~ime, the number of occupational accidents involving lathes decreased during the periods studied by almost half, from 194 to 103. The accident frequency fell from 81 to 46; this difference is statistically significant, in the 12 target enterprises, too, the number of occupational accidents decreased clearly, from 60 to 22. The accident frequency fell from 164 to 55, which is a statistically significant drop. The number of lathe accidents decreased as the sat'eguarding of lathes improved. The number of lathe accidents did not, however, correlate directly with the safeguarding of lathes. However, it seems obvious that safeguards have significant effect on lathe accidents, but safety cannot be merely guaranteed by safeguards. Attention must be paid also to safe working practices. Keywords: Accident prevention; Evaluation of protective equipment; Effects of protective equipment; Metal lathe work
I. Introduction
In the late 1970s, the Finnish industrial safety authorit,~es focused attention on the high number of accidents occurring during lathe work. The LZOour Protection District of H~ime decided to start a project the objectives of which were to determine the accident risks in metal cutting and to find measures by which their oc,:urrence could be reduced. A study investigating these issues was carried out in 1980 (Varonen, 1982). On the basis of the Elsevier Science B.V. SSD10925-7535 (94) 00059-X
16
U. Varonen / Safety Science 21 (1995) 15-22
results, safety inspectors started to instruct and advise enterprises on how to improve the safeguarding of lathes. The outcome of some field studies gave reason to assume that improving the safeguarding of lathes would reduce the number of accidents occurring durmg lathe work. When powerpresses were equipped with two-hand controls or other similar safety devices, for instance, the number of injuries to the hands fell drastically (Suokas, 1983). In the case of chain saws, chain brake and anti-kickback devices reduced the number of injuries among forestry workers (Klen and V~iyrynen, 1983). The purpose of the present study was to determine (i) the type and extent of changes that have occurred in the safeguarding of lathes in the province of H~ime from 1981 to 1986, and (ii) whether the changes in safeguarding that had occurred had brought about changes in the number, type or severity of accidents involving lathes.
2. Materials and methods 2. I. The stu@ on the whole province of Hi, me
During study period I, i.e. from July 1, 1981 to June 30, 1982, safety inspectors studied 726 lathes in 98 enterprises located in the province of H~me. These studies were carried out as part of the safety inspectors' normal inspection activities. During study period II, i.e. from January 1 to December 31, 1986, a random sample of 5% of the enterprises within the entire province was chosen as objects of study. Of the enterprises included in the sample, 27 had 110 lathes. These lathes were studied by the author. To determine the safety level of the lathes, a 12-point checklist was filled in for each lathe, The list was used to investigate whether the lathe had appropriate safety devices to prevent hazards caused by (i) handling of swarf- long string-like chips (chip puller) (ii) flying chips (chip shield) (iii) rotating chuck (chuck guard) (iv) workpieces extending through the head stock (v) accidental start-ups (vi) entanglement to the workpiece etc. (emergency stop) (vii) handling of heavy workpieces (hoist) (viii) rotating cranks with handles (ix) Iooseuing ofachuck ix) long run-down-time of a lathe (brake) (xi) poor quality of cutting fluids (xii) poor lighting During study period II, the use of goggles or face shields was also determined. The reliability of the study method was checked by having two researchers simultaneously study the safeguarding of 54 lathes in four enterprises. The agreement between the researchers was calculated as follows (Fellner and Sulzer-Azaroff, 1984):
U. Varonen/Safety Science 21 (1995) 15-22
i7
Fig. I. Some typical safety devices of manually operated turning lathes: ( 1) chip puller, (2) chip shield,(3) chuck guard, (4) protection against workpieces extending through the head stock, (5) prevention of accidental startups, (6) emergency stop.
agreement % =
agreement × 100% agreement + disagreement
Agreement as to the existence of hazards was 91-100% (mean 96%), that for the adequacy of safety measures being 94-98% (mean 96%). The validity of the method was not examined. On the other hand, when the actual variables (the existence of hazards and the adequacy of the safety measures) were measured, the situation was tbund to be logically valid. To find out the number and type of accidents involving lathes, reports prepared by employers on industrial accidents that occurred at lathes during study periods I and II and that were included in Finland's official statistics on industrial accidents were analyzed. The material comprised occupational accidents occurring in the province of H~ime that had led to disability of at least three days, the day of the accident excluded. Supplementary information was acquired in cases when it was not possible on the basis of an accident report to determine how the accident had happened. Enquiries of this type were made for 58 cases in study period I and tbr 33 cases in study period II. 2.2. The study on 12 target enterprises
Betbre study period II, 12 of the 98 enterprises studied during study period I were selected for the target group. These enterprises had had an exceptional number of lathe accidents
!8
U. Varonen ~Safety Science 21 (1995) 15-22
during study period I, after which they had paid special attention to improving the safeguarding of their lathes. At the time of study period I, the 12 target enterprises possessed 192 lathes. These enterprises had 20 '~ lathes at the time of study period II. The safeguarding of these lathes was studied using a checklist, in the manner described above. For study period II, none of 12 target enterprises was included in the random sample of 27 enterprises, which represented 5% of all enterprises in the whole province of H~ime. The accidents involvins lathes which had occurred in these 12 target enterprises during study periods I and ii were analyzed as described above.
3, Results
3. !. The study on the whole province of Hame In the province of H/ime, the proportion of manually-operated turning lathes decreased by almost 20% from study period I to study period II, but the proportion of CNC lathes and other automatic lathes rose by almost 10% (Table 1). As to the first five points of the checklist, the safeguarding of lathes in study period II was clearly better than in study period I (Table 2). The safety measures taken in the enterprises, e.g. new chip shields or chuck guards, explain 55% and the purchasing of new and better safeguarded lathes explain 45% of the improvement in the safeguarding of lathes. There were no changes as to the severity of accidents involving lathes from study period I to study period II. The number of accidents involving lathes was reduced by almost half of the previous figure, being 194 for the whole province of Hiime during study period I and 103 during study period II. The accident frequency (number of accidents l0 t' per hours worked with lathes) fell from 81 to 46. This decline is statistically significant (p < 0.001; ,~-test). Table I Lathes studied in the province of Hfime during study periods ! (July !, 1981-June 30, 1982) and II (January l December 3 I, 1986), classified by the type of lathes Type of lathes
Proportion of lathes studied Study period !I
l
( 1 ) Manually operated turning lathes (2) Turret lathes ( 3 ) NC, CNC and other automatic lathes (4) Others Lathes studied
72% 9% 12% 7% 726
55% 16% 20% 8% I 10
U. Varonen ~Safety Science 21 (1995) 15-22
19
Table 2 Defects found in the safeguarding of lathes in the province of Hfime during study periods ! (July !, 1981-June 30, 1982) and 11 (January I-December 31, 1986) Safety defect in the lathe
Proportion of faulty lathes among all lathes studied Study period I
!I
(I)
Chip puller totally absent or inappropriate
65% p < 0.05 (X2-test)
52%
(2)
Chip shield totally absent or inappropriate
58% p < 0.00 I
36%
(3)
Chuck guard totally absent or inappropriate
62% p<0.001
41%
(4)
No protection against workpieces extending through the head stock
20% p<0.001
6%
(5)
Accidental start-ups not prevented
38% p<0.01
23%
Nmnber of lathes studied
726
II0
Table 3 Lathe accidenis occurring in the province of Htime during study periods ! (July I, 1981-June 30, 1982) and I! (January i-December 3 I, 19~6), classified by the safety devices that may have been able to prevent the accident. The classification was made by three safety inspectors familiar with the safety of lathe work Safety device which may have been able to prevent the accident
Number of accidents Study period 11
!
( I) (2 ) (3) (4) (5) (6) (7)
Total
Chip puller Chip shield Chuck guard Other safety device or measure Could not have been prevented by measured investigated in this study Disagreement Accidents that could not be classified due to the poor information in the accident reports
28 39 8 22 35
21 15 4 16 20
35 27
17 10
194
103
U. Varonen / Safety Science 21 (1995) 15-22
20
Table 4 Expected number of accidents calculated on the basis of reduced exposure to accident risks and the actual number of accidents in the province of H~ime during the period of January I-December 31, 1986 Safety device which may have prevented the accident
Expectation = Number of accidents which should have occurred when exposure to accident risks had been taken into account
Actual number of accidents from January ! to December 3 !, 1986
( I) (2) (3)
23 20 4
2i !5 4
Chip puller Chip shield Chuck guard
At the same time, the overall accident frequency in the whole province of H~ime fell from 56 to 53 (National Board of Labour Protection, 1982, 1983, 1987). The greatest drop occurred in the number of accidents that could be prevented by a chip shield, but the number of other types of accidents also fell clearly (Table 3). The improved safeguarding of lathes reduced the accident risk in lathe work. The number of accidents that had occurred during study period I and the reduced exposure to accident risk were used as the base for calculating the number of occupational accidents expected to occur during study period II. The result of the calculation correlated well with the actual number of accidents (Table 4). During study period II, 19% of the lathe operators used goggles or face shields. During the previous study on the safety of !athes, done in 1980 (Varonen, 1982), the corresponding figure had been 17%. 3.2. The study on 12 target enterprises
In the 12 target enterprises, the proportion of manually-operated turning lathes decreased by 10%, the proportion of CNC and other automatic lathes increasing by more than 10% from study period I to study period II (Table 5). Table 5 Lathes studied in the 12 target enterprises during study periods ! (July I, 1981-June 30, 1982) and il (January I-December 3 i, 1986), classified by the type of lathes Type of lathe~
Proportion of lathes studied Study period !!
i
( I) (2) (3) (4) Lathes studied
Manually operated turning lathes Vertical lathes NC, CNC and other automatic lathes Others
68% 9% 17% 6% 192
58% 8% 30% 4% 20 !
U. Varonen / Safety Science 21 (1995) 15-22
21
Table 6 Defects found in the safeguarding of lathes in 12 target enterprises during study periods I (July 1,198 l-June 30, 1982) and I1 (January l-December 31, 1986) Safety defect in the lathe
Proportion of faulty lathes among all lathes studied Study period I
II
( 1)
Chip puller totally absent or inappropriate
66% p < 0.001 (X2-test)
20%
(2)
Chip shield totally absent or inappropriate
60% P < 0.00 I
26%
(2)
Chuck guard totally absent or inappropriate
58% p < 0.001
37%
(4)
No protection against workpieces extending through the head ~tock
15% p < 0.05
7%
(5)
Accidental start-ups not prevented
32% p < 0.00 i
13%
(6)
Emergency stop totally absent or not inappropriate place
44% p < 0.001
23%
Number of lathes studied
192
201
As to the first six points of the checklist, the safeguarding of lathes was clearly better in study period I than in study period II (Table 6). The safety measures taken in the 12 target enterprises, e.g. new chip shields or chuck guards, explain 57% and the purchasing of new and better safeguarded lathes explain 43% of the improvement in the safeguarding of lathes. There were no changes as to the severity of accidents involving lathes from study period I to study period II. In the 12 target enterprises, the number of accidents involving lathes decreased to about one third of the previous figure, from 60 during study period I to 22 during study period II. Similarly, the accident frequency fell from 164 to 55; this drop is statistically significant (p < 0.001 ). At the same time, the overall accident frequency in the 12 target enterprises increased from 75 to 78.
4. Discussion
The number of accidents involving lathes can be decreased in many ways. The means available may include increased use of safety guards or goggles, or changes in working
22
U. Varonen / Safety Science 21 (1995) 15-22
methods and practices. Changes in workpiece material, in the complexity of workpieces or in the sizes of workpiece series may also affect the occurrence of accidents involving lathes. No significant increase in the use of goggles or face shields took place between 1980 and 1986. Thus, an increased use of personal protective equipment cannot explain the rapid decrease in the number of accidents involving lathes. There were no systematic changes in working methods other than the increased use of CNC lathes. Not only did this single factor reduce the most common types of accidents, such as those caused by flying chips, rotating workpieces and chuck; it also reduced the occurrence of many other types of accidents. The drop in occupational accidents as a result of the increased use of CNC lathes is due to the high constructional safety of CNC lathes, to the decreased use of certain dangerous working methods (e.g., grinding a workpiece with an abrasive tape or file), to the good auxiliary devices and instruments of CNC lathes, and to the fewer number of times when the lathe operator must intervene in lathe operation during working hours. On the other hand, there were no accidents caused by the risks inherent to CNC lathes (e.g., driving the tool against a rotating workpiece). Possible changes in workpiece material, the complexity of workpieces etc. were not investigated during this study. This study found that the number of accidents involving lathes decreased, while the safeguarding of lathes improved. It is thus clear that safeguards have a significant effect on lathe accidents. The safeguarding level of lathes did not, however, directly correspond to the number of occupational accidents involving lathes. This is because, in proportion to the volume of lathe work, more occupational accidents occurred in the 12 target enterprises than in the whole province of Hiime, despite the fact that the lathes in the 12 target enterprises were safegum'ded better than average. It thus seems clear that sate working with lathes cannot be guaranteed merely by safety devices, but that working methods and practices also need to be changed.
References Feliner, D,J, and Sulzer-Azaroff, V., 1984. Increasing industrial safety practices and conditions through posted f~dback. J. Safety Res,, 15: 7-21. Klen, T. and V~tyrynen, S., 1983. Hakkuumiehen henkil6kohtaisten suojainten ja moottorisahan turvalaitteiden merkitys ty6tapaturmien torjunnassa ja lievent~imisess~i. (The role of loggers' personal protectors and the safety devices of chain saws in the prevention or alleviation of injuries.) Institute of Occupational Health, Helsinki. ( in Finnish with an English abstract). Suoka,,. J,, 1983. The effect of power-press regulations in Finland. J. Occup. Accid., 5: I-8. Ty0tapawrmat 198 I, National Board of Labour Protection, 1982. Suomen Virallinen tilast XXV 1:33. ( Industrial accidents 198 I. The Official Statistics of Finland. ) National Board of Labour Protection, Tampere ( In Finnish with an English abstract), Ty(~t~,paturmat 1982, National Board of Labour Protection, 1983. Soomen Virallinen tilasto XXV !:34. ( Industrial accidents 1982. Official Statistics of Finland. ) National Board of Labour Protection. Tampere (In Finnish with an English abstract ). Ty6tapatun~at 1 9 ~ National Board of Labour Protection, 1987. Suomen Virallinen tilasto XXV !:38. ( Industrial accidents 1986. Official Statistics of Finland.) National Board of Labour Protection, Tampere (In Finnish with an English abstract). Varonen, U., 1982. Sorvaamisen turvailisuuden parantaminen (Improving the safety of lathe work). National Board of Labour Protection, Tampere (In Finnish with an English abstract).
Safety Science 21 (1995) 15-22
Safeguarding of lathes and occupational accidents Unto Varonen Labour Protection District of Hiime, Lahti. Finland Tampere Universityof Technology, Tampere. Finland
Accepted ! November 1994
Abstract
The purpose of the study was to determine whether better safeguarding of lathes used for metal cutting had affected the number of occupational accidents occurring during metal lathe work. The study consisted of two parts: (i) safeguarding of lathes and analysis of lathe accidents which occurred throughout the entire province of H~ime; and (ii) safeguarding of lathes and analysis of lathe accidents in 12 target enterprises. The safeguarding of lathes as well as the number and type of lathe accidents were studied from July I, 1981 to June 30, 1982, and again from January 1 to December 31, 1986. The safeguarding of lathes improved during the periods studied, both in the whole province of Hame and in 12 target enterprises. In the province of H~ime, the number of occupational accidents involving lathes decreased during the periods studied by almost half, from 194 to 103. The accident frequency fell from 81 to 46; this difference is statistically significant, in the 12 target enterprises, too, the number of occupational accidents decreased clearly, from 60 to 22. The accident frequency fell from 164 to 55, which is a statistically significant drop. The number of lathe accidents decreased as the sat'eguarding of lathes improved. The number of lathe accidents did not, however, correlate directly with the safeguarding of lathes. However, it seems obvious that safeguards have significant effect on lathe accidents, but safety cannot be merely guaranteed by safeguards. Attention must be paid also to safe working practices. Keywords: Accident prevention; Evaluation of protective equipment; Effects of protective equipment; Metal lathe work
I. Introduction
In the late 1970s, the Finnish industrial safety authorit,~es focused attention on the high number of accidents occurring during lathe work. The LZOour Protection District of H~ime decided to start a project the objectives of which were to determine the accident risks in metal cutting and to find measures by which their oc,:urrence could be reduced. A study investigating these issues was carried out in 1980 (Varonen, 1982). On the basis of the Elsevier Science B.V. SSD10925-7535 (94) 00059-X
16
U. Varonen / Safety Science 21 (1995) 15-22
results, safety inspectors started to instruct and advise enterprises on how to improve the safeguarding of lathes. The outcome of some field studies gave reason to assume that improving the safeguarding of lathes would reduce the number of accidents occurring durmg lathe work. When powerpresses were equipped with two-hand controls or other similar safety devices, for instance, the number of injuries to the hands fell drastically (Suokas, 1983). In the case of chain saws, chain brake and anti-kickback devices reduced the number of injuries among forestry workers (Klen and V~iyrynen, 1983). The purpose of the present study was to determine (i) the type and extent of changes that have occurred in the safeguarding of lathes in the province of H~ime from 1981 to 1986, and (ii) whether the changes in safeguarding that had occurred had brought about changes in the number, type or severity of accidents involving lathes.
2. Materials and methods 2. I. The stu@ on the whole province of Hi, me
During study period I, i.e. from July 1, 1981 to June 30, 1982, safety inspectors studied 726 lathes in 98 enterprises located in the province of H~me. These studies were carried out as part of the safety inspectors' normal inspection activities. During study period II, i.e. from January 1 to December 31, 1986, a random sample of 5% of the enterprises within the entire province was chosen as objects of study. Of the enterprises included in the sample, 27 had 110 lathes. These lathes were studied by the author. To determine the safety level of the lathes, a 12-point checklist was filled in for each lathe, The list was used to investigate whether the lathe had appropriate safety devices to prevent hazards caused by (i) handling of swarf- long string-like chips (chip puller) (ii) flying chips (chip shield) (iii) rotating chuck (chuck guard) (iv) workpieces extending through the head stock (v) accidental start-ups (vi) entanglement to the workpiece etc. (emergency stop) (vii) handling of heavy workpieces (hoist) (viii) rotating cranks with handles (ix) Iooseuing ofachuck ix) long run-down-time of a lathe (brake) (xi) poor quality of cutting fluids (xii) poor lighting During study period II, the use of goggles or face shields was also determined. The reliability of the study method was checked by having two researchers simultaneously study the safeguarding of 54 lathes in four enterprises. The agreement between the researchers was calculated as follows (Fellner and Sulzer-Azaroff, 1984):
U. Varonen/Safety Science 21 (1995) 15-22
i7
Fig. I. Some typical safety devices of manually operated turning lathes: ( 1) chip puller, (2) chip shield,(3) chuck guard, (4) protection against workpieces extending through the head stock, (5) prevention of accidental startups, (6) emergency stop.
agreement % =
agreement × 100% agreement + disagreement
Agreement as to the existence of hazards was 91-100% (mean 96%), that for the adequacy of safety measures being 94-98% (mean 96%). The validity of the method was not examined. On the other hand, when the actual variables (the existence of hazards and the adequacy of the safety measures) were measured, the situation was tbund to be logically valid. To find out the number and type of accidents involving lathes, reports prepared by employers on industrial accidents that occurred at lathes during study periods I and II and that were included in Finland's official statistics on industrial accidents were analyzed. The material comprised occupational accidents occurring in the province of H~ime that had led to disability of at least three days, the day of the accident excluded. Supplementary information was acquired in cases when it was not possible on the basis of an accident report to determine how the accident had happened. Enquiries of this type were made for 58 cases in study period I and tbr 33 cases in study period II. 2.2. The study on 12 target enterprises
Betbre study period II, 12 of the 98 enterprises studied during study period I were selected for the target group. These enterprises had had an exceptional number of lathe accidents
!8
U. Varonen ~Safety Science 21 (1995) 15-22
during study period I, after which they had paid special attention to improving the safeguarding of their lathes. At the time of study period I, the 12 target enterprises possessed 192 lathes. These enterprises had 20 '~ lathes at the time of study period II. The safeguarding of these lathes was studied using a checklist, in the manner described above. For study period II, none of 12 target enterprises was included in the random sample of 27 enterprises, which represented 5% of all enterprises in the whole province of H~ime. The accidents involvins lathes which had occurred in these 12 target enterprises during study periods I and ii were analyzed as described above.
3, Results
3. !. The study on the whole province of Hame In the province of H/ime, the proportion of manually-operated turning lathes decreased by almost 20% from study period I to study period II, but the proportion of CNC lathes and other automatic lathes rose by almost 10% (Table 1). As to the first five points of the checklist, the safeguarding of lathes in study period II was clearly better than in study period I (Table 2). The safety measures taken in the enterprises, e.g. new chip shields or chuck guards, explain 55% and the purchasing of new and better safeguarded lathes explain 45% of the improvement in the safeguarding of lathes. There were no changes as to the severity of accidents involving lathes from study period I to study period II. The number of accidents involving lathes was reduced by almost half of the previous figure, being 194 for the whole province of Hiime during study period I and 103 during study period II. The accident frequency (number of accidents l0 t' per hours worked with lathes) fell from 81 to 46. This decline is statistically significant (p < 0.001; ,~-test). Table I Lathes studied in the province of Hfime during study periods ! (July !, 1981-June 30, 1982) and II (January l December 3 I, 1986), classified by the type of lathes Type of lathes
Proportion of lathes studied Study period !I
l
( 1 ) Manually operated turning lathes (2) Turret lathes ( 3 ) NC, CNC and other automatic lathes (4) Others Lathes studied
72% 9% 12% 7% 726
55% 16% 20% 8% I 10
U. Varonen ~Safety Science 21 (1995) 15-22
19
Table 2 Defects found in the safeguarding of lathes in the province of Hfime during study periods ! (July !, 1981-June 30, 1982) and 11 (January I-December 31, 1986) Safety defect in the lathe
Proportion of faulty lathes among all lathes studied Study period I
!I
(I)
Chip puller totally absent or inappropriate
65% p < 0.05 (X2-test)
52%
(2)
Chip shield totally absent or inappropriate
58% p < 0.00 I
36%
(3)
Chuck guard totally absent or inappropriate
62% p<0.001
41%
(4)
No protection against workpieces extending through the head stock
20% p<0.001
6%
(5)
Accidental start-ups not prevented
38% p<0.01
23%
Nmnber of lathes studied
726
II0
Table 3 Lathe accidenis occurring in the province of Htime during study periods ! (July I, 1981-June 30, 1982) and I! (January i-December 3 I, 19~6), classified by the safety devices that may have been able to prevent the accident. The classification was made by three safety inspectors familiar with the safety of lathe work Safety device which may have been able to prevent the accident
Number of accidents Study period 11
!
( I) (2 ) (3) (4) (5) (6) (7)
Total
Chip puller Chip shield Chuck guard Other safety device or measure Could not have been prevented by measured investigated in this study Disagreement Accidents that could not be classified due to the poor information in the accident reports
28 39 8 22 35
21 15 4 16 20
35 27
17 10
194
103
U. Varonen / Safety Science 21 (1995) 15-22
20
Table 4 Expected number of accidents calculated on the basis of reduced exposure to accident risks and the actual number of accidents in the province of H~ime during the period of January I-December 31, 1986 Safety device which may have prevented the accident
Expectation = Number of accidents which should have occurred when exposure to accident risks had been taken into account
Actual number of accidents from January ! to December 3 !, 1986
( I) (2) (3)
23 20 4
2i !5 4
Chip puller Chip shield Chuck guard
At the same time, the overall accident frequency in the whole province of H~ime fell from 56 to 53 (National Board of Labour Protection, 1982, 1983, 1987). The greatest drop occurred in the number of accidents that could be prevented by a chip shield, but the number of other types of accidents also fell clearly (Table 3). The improved safeguarding of lathes reduced the accident risk in lathe work. The number of accidents that had occurred during study period I and the reduced exposure to accident risk were used as the base for calculating the number of occupational accidents expected to occur during study period II. The result of the calculation correlated well with the actual number of accidents (Table 4). During study period II, 19% of the lathe operators used goggles or face shields. During the previous study on the safety of !athes, done in 1980 (Varonen, 1982), the corresponding figure had been 17%. 3.2. The study on 12 target enterprises
In the 12 target enterprises, the proportion of manually-operated turning lathes decreased by 10%, the proportion of CNC and other automatic lathes increasing by more than 10% from study period I to study period II (Table 5). Table 5 Lathes studied in the 12 target enterprises during study periods ! (July I, 1981-June 30, 1982) and il (January I-December 3 i, 1986), classified by the type of lathes Type of lathe~
Proportion of lathes studied Study period !!
i
( I) (2) (3) (4) Lathes studied
Manually operated turning lathes Vertical lathes NC, CNC and other automatic lathes Others
68% 9% 17% 6% 192
58% 8% 30% 4% 20 !
U. Varonen / Safety Science 21 (1995) 15-22
21
Table 6 Defects found in the safeguarding of lathes in 12 target enterprises during study periods I (July 1,198 l-June 30, 1982) and I1 (January l-December 31, 1986) Safety defect in the lathe
Proportion of faulty lathes among all lathes studied Study period I
II
( 1)
Chip puller totally absent or inappropriate
66% p < 0.001 (X2-test)
20%
(2)
Chip shield totally absent or inappropriate
60% P < 0.00 I
26%
(2)
Chuck guard totally absent or inappropriate
58% p < 0.001
37%
(4)
No protection against workpieces extending through the head ~tock
15% p < 0.05
7%
(5)
Accidental start-ups not prevented
32% p < 0.00 i
13%
(6)
Emergency stop totally absent or not inappropriate place
44% p < 0.001
23%
Number of lathes studied
192
201
As to the first six points of the checklist, the safeguarding of lathes was clearly better in study period I than in study period II (Table 6). The safety measures taken in the 12 target enterprises, e.g. new chip shields or chuck guards, explain 57% and the purchasing of new and better safeguarded lathes explain 43% of the improvement in the safeguarding of lathes. There were no changes as to the severity of accidents involving lathes from study period I to study period II. In the 12 target enterprises, the number of accidents involving lathes decreased to about one third of the previous figure, from 60 during study period I to 22 during study period II. Similarly, the accident frequency fell from 164 to 55; this drop is statistically significant (p < 0.001 ). At the same time, the overall accident frequency in the 12 target enterprises increased from 75 to 78.
4. Discussion
The number of accidents involving lathes can be decreased in many ways. The means available may include increased use of safety guards or goggles, or changes in working
22
U. Varonen / Safety Science 21 (1995) 15-22
methods and practices. Changes in workpiece material, in the complexity of workpieces or in the sizes of workpiece series may also affect the occurrence of accidents involving lathes. No significant increase in the use of goggles or face shields took place between 1980 and 1986. Thus, an increased use of personal protective equipment cannot explain the rapid decrease in the number of accidents involving lathes. There were no systematic changes in working methods other than the increased use of CNC lathes. Not only did this single factor reduce the most common types of accidents, such as those caused by flying chips, rotating workpieces and chuck; it also reduced the occurrence of many other types of accidents. The drop in occupational accidents as a result of the increased use of CNC lathes is due to the high constructional safety of CNC lathes, to the decreased use of certain dangerous working methods (e.g., grinding a workpiece with an abrasive tape or file), to the good auxiliary devices and instruments of CNC lathes, and to the fewer number of times when the lathe operator must intervene in lathe operation during working hours. On the other hand, there were no accidents caused by the risks inherent to CNC lathes (e.g., driving the tool against a rotating workpiece). Possible changes in workpiece material, the complexity of workpieces etc. were not investigated during this study. This study found that the number of accidents involving lathes decreased, while the safeguarding of lathes improved. It is thus clear that safeguards have a significant effect on lathe accidents. The safeguarding level of lathes did not, however, directly correspond to the number of occupational accidents involving lathes. This is because, in proportion to the volume of lathe work, more occupational accidents occurred in the 12 target enterprises than in the whole province of Hiime, despite the fact that the lathes in the 12 target enterprises were safegum'ded better than average. It thus seems clear that sate working with lathes cannot be guaranteed merely by safety devices, but that working methods and practices also need to be changed.
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