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Accident risks and the effect of performance feedback with industrial CO2 lasers
Accident risks and the effect with performance feedback industrial CO2 lasers H. LAITINEN,
of
T. J;iRVINEN
A safety survey of seven industrial CO2 lasers was carried out in order to discover the hazards, the incidents which have occurred, and perceived safety risks. A safety behaviour modification programme was developed and implemented in one laser workshop. Beam related incidents were not as rare as was expected on the basis of earlier analyses and reported accidents. Most incidents, however, related to the materials handling in the workstation. The performance feedback improved safety behaviour effectively. The baseline safety level was 50%, and during the feedback it rose up to 90%, while two months after the feedback it was 72%. KEYWORDS:
laser safety, risks, performance
Introduction There are safety and health risks connected with the laser beam that traditional technology lacks. The invisible beam can not only process metals but can also burn skin, damage the eye and cause fire. For example, an unfocused raw beam of a typical 1.5 kW laser is dangerously effective up to a distance of more than 100 m. A focused and reflected beam diffuses more quickly, but is still effective up to 10 m from the lens’. A beam reflecting from a glossy surface burns skin into blisters and, for example, sets cotton on fire in less than a second. Except for invisible infra-red light, ultra-violet and wide-band light radiation generated when processing with the CO, lasers, the radiation density may exceed the safe recommended maximum radiation doses even at distances of 1 m from the workpiece’. Laser safety standards are aimed especially at preventing the escape of beams. The beam may escape for a number of reasons: there is a dirty surface (mirror, lens) in the beam delivery system; there is mechanical or heat damage in the delivery system; there is an error function in the software or other control system, human error in maintenance, and a defective or missing workpiece3. With fault tree
HL is at The Finnish Institute of Occupational Health, Laajaniityntie 1, FIN-01 620 Vantaa, Finland. TJ is at Lappeenranta University of Technology, Box 20, FIN-53851 Lappeenranta, Flnland. Received 13 April 1994.
0030-3992/95/$10.00 Optics & Laser Technology Vol 27 No 1 1995
@ 1995
feedback,
lasers (CO,)
analysis, it has been calculated that the escape probability per laser unit is 1 x 10m2 - 1 x 10m3; in other words one occurrence per hundred years, at the most4. One can only guess the number of accidents related to the use of lasers. In the reported couple of hundred cases, the majority of accidents have involved eye injuries, most of which were caused by lasers other than the CO, laser. In addition, at least four deaths caused by electric shock were reported ten years ago’. In practice, the number of beam incidents seems to be much higher, with most of the incidents not reported2,6. The users of CO, lasers do not subjectively consider the beam as a great hazard, neither do they usually use safety goggles during normal processing’. It is no wonder, that negligence in using goggles is often mentioned in laser accident reports. Safety training for new laser operators and updated training programmes for all personnel are recommended to minimize human errors. The effect of safety training for laser personnel has not been studied, however. Studies in some other fields of safety show that training and giving information alone has no (or only minimal) effect on performance 8-9. In changing behaviour, good results have been achieved by giving positive feedback (reinforcement) of desired, safe behaviour. A positive reinforcement can modify behaviour; for instance, the use of personal protective devices, the use of safety equipment, working postures, using working tools, driving a forklift truck and industrial housekeeping’“~’ ‘. Elsevier
Science.
All rights
reserved
25
Accident
risks and the effect of performance
feedback:
The aim of this study was to survey the safety situation in Finnish laser workshops. In particular, the main focus was to find out which kinds of laser accidents and incidents have occurred. These results were compared with earlier analyses in the laser laboratory of Lappeenranta University of Technology (LUT)‘. The question was whether the same risks exist in industrial laser workshops, and also whether there are some additional risks that are different from the laboratory use of the laser. A secondary aim was to study the subjective risk assessment and safety behaviour of laser operators, while it was also desired to develop and test a safety programme for laser workshops, based on the principles of positive feedback. Material Target
and
methods
enterprises
and lasers
The analyses were carried out in three laser workshops and an Adult Training Centre (ATC). In all, five CO, lasers were analysed. The three workshops mainly subcontracted laser processing, mostly metal cutting. The number of the workers in the workshops varied from two to six. The ATC used lasers for teaching laser users. but it also leased a laser for production use. The results were compared with the earlier analyses of two lasers in LUT, which are used for research (Table I). The lasers analysed represented a wide range of laser producers, there were German, English, Swiss, American and Japanese devices. Their powers varied from 0.85 kW to 2.5 kW. In one case, the workstation was based on a stable beam and a mobile workpiece. while in all the others the situation was reversed. Methods
H Laitinen and T. Jarvinen particularly asked whether the near accidents and hazards found in the LUT laboratory were also relevant in each workshop. Interviews and group works were carried out to discover the incidents and perceived problems in laser workshops. Technical and organizational improvements were also developed in group works. All the group works lasted about l-l.5 hours. The agenda for each group work was as follows: (1) everybody generated ideas independently; (2) the ideas were presented; (3) additional ideas were generated; (4) the additional ideas were presented; (5) there was voting for the most important ideas (only one ‘own idea’ could be voted for) and (6) the ideas were grouped in order of importance. In the Adult Training Centre two laser teachers and a class of laser students took part in the group work. In Workshop 2 and Workshop 3 all the laser personnel participated. An experiment to develop the laser safety behaviour programme was carried out in Workshop 2. A group work involving all personnel was used to set the performance targets. The checklist for measuring the performance was prepared by the researchers, who also carried out all the observations. The number of items in the checklist was 89. Each item observed was marked as being either correct or incorrect (the third alternative was ‘not observed’, if the item temporarily could not be observed). The result was calculated as a performance index, which was the percentage of items observed to be correct from all items observed. To measure the baseline. four observation tours were done without any feedback. After that, a large index chart was posted on the wall with the results of baseline observations. The observations were performed once or twice a week and the new results were marked on the chart immediately. Results
In LUT. a hazard and operability study of the beam delivery system, and work safety analyses of cutting, welding and alloying. were carried out. The staff was also interviewed, and they reported near accidents with a report form (Table 2). Observations and informal interviews were carried in the laser workshops. In interviews it was Table 1. Target
enterprises
and their
out
Near accidents Laser beams had caused near accidents and problems in all enterprises (Table 3). The most common incidents
involved
slight damage
to the workstation
due to the reflected beam. Finger injuries caused by the straight beam, and potentially severe accidental starting of the laser beams had also occurred.
laser devices
Enterprise
Laser
Workstation
Use of the laser
LUT
Conrol Laser CLL 2500, 2.5 kW Rofin Sinar RS6000, 6 kW Coherent Everlaser S 48 0.82 kW Bylas BL 1500, 1.5 kW Mazak L32 1.5 kW Trumpf TLF 2000, 2 kW Photon sources P2500 2.5 kW
Control Laser, 2500 x 3500, Linear Station, 1500 ASEA 1 FIB2000 Robot station Trumpf-sheet workstation: Stable beam - mobile sheet Bylas 1500 x 3000 Mazak 1225, 1250 x 2500 Trumatic L3003, 1500 x 1000 Laser Work LW 2000 x 6000
2D and 3D cutting, welding and surface treatment; research and training 2D cutting in two shifts, 1 worker / shift 2D cutting, 3 workers 2D and 3D cutting and welding, 6 workers 2D and 3D cutting and welding; training of designers and users, operating time is leased to enterprises
Workshop
1
Workshop Workshop
2 3
Adult Training Centre (ATC)
Optics & Laser 26
Technology
Vol 27 No 1 1995
Accident
Table
2. The methods
risks and the effect
of performance
feedback:
H. Laitinen
and T. Jirvinen
of the study
Methods
LUT
ATC
Workshop
1
Workshop
2
Workshop
3
Analyses HAZOP of the beam delivery system Work Safety Analysis Near accident reporting form Interviews Problem and incident analysis, group work
Planning l
group
technical
l l l
X
X
X X
X
X
X
X
X
X
X
X
X
X
measures
work
Laser safety l
X
performance
programme
setting performance targets, group work preparing a check list for observations measuring the base line giving feedback
In all the laser workshops, the beam was reflected back to the mirror system and the resonator when trying to cut copper, aluminium or brass. The beam is reflected back if it does not pierce the sheet quickly enough. This leads to damage to the resonator mirror. Either splashes of molten metal or the reflected beam had caused small fires in the workstation, thus damaging the equipment. The relay of the temperature controller of the resonator oven was stuck twice and caused overheating of the oven. Staff noticed all the fire incidents in time and used extinguishers to prevent a fire. In some cases, the focusing lenses were worn out, which eventually melted and vaporized the lenses. With one of the lasers, the maintenance man had received an electric shock when servicing the resonator. Although he was said to have been quiet that day, there were no other more serious consequences.
Table Type
Many near accidents and problems connected with workstations had occurred. With all l.he workstations using a stable workpiece and a mobile beam, the vertical turning of the cut-off workpieces was a problem. The cut-off workpieces often turned into the upright position and so caused a risk of a collision between the cutting head and the workpiece. When this problem occurred, the worker had to stop cutting and remove the workpiece. This often required stepping on the worktable, which may have led to accidents. In order not to interrupt production. cuttmg was sometimes left on while removing the workpiece, and there was the risk of becoming crushed between the automatically moving parts. This type of near accident had also occurred. The handling of the sheet was automated at one workstation, where the beam was stable and the workpiece moved. Due to the automation, the laser
3. Laser incidents of incident
Number LUT
Beam related l l l l l l
l
related
Materials handling related incidents the cut piece of the sheet turns into an upright
l
workshops
near accident when from the workstation, near accident while
Optics & Laser Technology Vol 27 No 1 1995
8 10 3
1
1 severa I 1 2 4 1
incidents
electric shock to the service man overheating the resonator oven due to the fault in the relay
l l
ATC and three
incidents
focused beam burns finger, hair, or safety mask reflections burn tracks to the equipment in workstation accidental start-up of the beam small fire caused by the reflections or splashes of molten metal in the workstation the beam reflects back to the resonator explosion or vaporization of the lens
Resonator l
of incidents
position the user is removing the workpiece while the machine runs lifting or moving the sheet
1
2
daily incident several several
27
Accident
risks and the effect of performance
feedback:
could function for long periods of time, even without personnel. However, some disturbances occurred. Sometimes, the cut workpiece got stuck in the sheet, and the worker had to release it. On one of these occasions, the automatically closed hatch had squeezed the hand of the worker, and if the sheet had started to move, it might have severed the hand. Fortunately. another worker, who happened to be in the same room, stopped the machine.
Subjective
risk assessment
The largest safety problems were how to handle the sheets safely and without scratching them, and also how to remove the workpieces from the workstation. Suction cup lifters, for example, were considered hazardous, especially for lifting the remnant sheet after cutting. In addition, the case when a piece of sheet had turned into the upright position, such that the worker had to step on the worktable to remove it, was a problem (Tables 4 and 5).
H. Laitinen and T. Jtirvinen Table 5. The perceived the Workshop 3 Occupational problems
I. High voltage parts in the resonator 2. Sheet handling manually and with the sucker cup lifter 3. Removing the cut workpiece while the machine runs 4. Risks during adjustment of the beam 5. Air impurities 6. Splashes of molten metal 7. Reflection of the beam when cutting Al, Cu and MS
The following Technical
safety
technical
in
1. Handling of sheets (lifts and transportation) safely and without scratching them 2. Marking and packing the completed workpieces 3. Adjustment times, should be shortened by better planning 4. Keeping tools and materials in order 5. Lacking documentation of disturbances 6. Allocation of the work between separate lasers 7. Cleaning when the shift finishes
measures
were implemented:
improvements
Nine improvements were developed Workshop 3, five of them had been nine months after the group work. improvements were developed and
priority
Workshop
Adult
2
tool chests for necessary tools; containers for waste pieces of sheet; new lifting and moving equipment for sheets; repair of the exhaust ventilation; new personal protective devices (safety masks); a guide for new laser users (ATC).
by the group in implemented In the ATC, seven six implemented.
Table 4. The perceived the work
of problems
in Effects
Training
Centre
(ATC) I. Ventilation 2. Problems in handling of sheet and workpiece 3. Wear and tear of safety devices and other laser equipment 4. Lacking documentation of maintenance and disturbances 5. Adjustment of the laser, when the shift changes 6. Problems in finding tools, spare parts and documents 7. Failure to user personal protective devices
Lack of easy instructions for the beginner Lack of information of correct processing parameters and cutting gas for different materials Lack of instructions for disturbance removal Difficult procedure for teach-in programming Problems in sheet handling Risk of the cutting head bumping into the upright turned piece of sheet Removing the cut workpiece while the machine runs
of the performance
The performance follows:
targets
feedback
in the Workshop
2 were as
(1) return the tools after use to their own places; (2) put the left-over pieces and scraps in their own places; put the spare parts in their own places; keep documents and disks in order; keep workplaces clean; use the personal protective devices, when needed; set the laser controllers into the normal position when the operator stops working; actions and (8) keep a record book of maintenance disturbances. (3) (4) (5) (6) (7)
The baseline performance measurements indicated that the performance level was very constant, slightly below 50% (Fig. 1). The overall index started to rise immediately after the feedback. The average index was 80% during the 13 weeks of feedback. The increase was highly significant when tested with the chi-square test using the frequencies of ‘correct’ and ‘incorrect’ observations (p = 7 x 10-40). When the feedback was discontinued, the average index of the follow-up
Optics
28
of problems
Problems with the fluency of work
safety
Inefficient ventilation, air impurities and electric hazards were also problematic. Laser users also felt that the documentation of disturbances and maintenance was not being done as it should be and that the tools and materials should be kept in better order.
priority
& Laser Technology Vol 27 No 1 1995
Accident 100
-
90
.-
80
.-
risks and the effect of performance
0
follow-up
:
:
:
:
:
:
:
.
:
:
:
f
2
4
6
R
10
12
14
16
I8
20
22
24
week
Fig
H. Laitinen and T. Jtirvinen
The removal of air impurities worked well in a stable beam workstation, and also when the workstation was totally enclosed, but only if the doors and covers were closed. Otherwise air impurities were considered a problem. The target ventilation systems are being studied and developed in the EU-643 project.
feedback
07
feedback:
1 The performance
index
in laser Workshop
2
observations was 74X-significantly higher than the baseline (p = 1 x lo- “). One reason for the slight decrease from the highest level was the installation of one new machine in the laser room during the follow-up period. Discussion Laser beams had caused incidents and problems in all the target laser workshops. The incidents covered all the escape possibilities of the beam-which Green3 has listed. The number of near accidents exceeded the probabilities that have been calculated with fault tree analysis4 approximately a hundred times. The reason for this may be underestimating or ignoring the significance of human factors in the fault tree analysis. It was surprising that, despite the risk situations, the hazards of the beam were not considered a significant problem in any of the enterprises. In particular, the reflected beam was not even considered dangerous to the eyes. This was probably why safety goggles were not used when cutting (except in the Adult Training Centre). The same observation has also been made in Germany7. The fact that the beam is considered harmless, may be partly due to the information given by the manufacturers, who emphasize that the infra-red ray of a CO, laser is harmless to the eyes compared with other lasers. However, when it comes to high power lasers. this statement is misleading. Either splashes of molten metal or the reflected beam had caused small fires in a workstation and damaged the equipment. This indicated that materials that are too flammable are used in workstation construction. The component faults of the laser itself can also cause fire hazards. The service work and documentation of disturbances was considered a problem in the workshops; nothing was done to rectify the situation. In the laser workshops, problems in material handling from the point of view of occupational safety and the smooth flow of the work were emphasized. In every workshop there were problems with the workpieces, which had been cut from the sheet. Little workpieces often turned into an upright position, and this was the biggest single problem connected with the workstation. Trials were carried out to form a better lamella construction under the sheet but with limited results.
Optics & Laser Technology Vol 27 No 1 1995
Noise was not considered a problem in any of the places of employment within this survey. Compared with a conventional machine workshop the laser halls were very quiet. Thus, the laser for its part solves the problem of noise, which is one of the major problems of occupational safety in machine workshops.
The feedback improved performance effectively, as it has done in earlier studies”. It is obvious that the feedback procedure was the agent for change, and no other contributing factors were simultaneously present. The feedback programme is a promising tool for laser workshops in improving the safety behaviour, maintenance performance and industrial housekeeping. Problems in these areas are known to cause accidents, production disturbances, material damage, quality problems, waste of time, and dissatisfaction among workers. Better performance should simultaneously improve the safety and productivity.
Conclusions The following this study.
conclusions
are made on the basis of
(1) A proper enclosure
of the workstation can solve several safety problems effectively: the reflections of the beam are stopped by the enclosure; air impurities are contained and the local ventilation can be cheaply solved; the enclosure can be fire protected by automatic fire extinguishers. (2) The worktable should be improved so that there is no possibility of the workpiece turning into an upright position. (3) An effective machine would also require better planning and mechanization in sheet handling. Materials handling has not been sufficiently taken into consideration in the research of laser safety, nor has it been dealt with in the EU-643 project. (4) The training of laser users has been mainly organized by the manufacturers and import companies. This is insufficient when it comes to safety. The dangers of reflections are underrated and there is little information about air impurities. Training materials for laser users are needed. The hazards of the beam and reflections, as well as the hazards of air impurities have to be presented simply and dependably. (5) More studies should be carried out to standardize and test the laser safety performance feedback programme for laser workshops. The behaviour modification approach should be covered in the syllabus of laser safety officer courses.
29
Accident
risks and the effect of performance
feedback:
H. Laitinen and T. Jarvinen
References 1 Rockwell, R. James, Jr., Moss, C.E. Optical radiation hazards of laser welding processes. Part II: CO, laser, Am Ind Hyg Assoc J W(8) (1989) 419427 2 Hietanen, M., Honkasalo, A., Laitinen, H., Lindroos, L., Welling, 1. and Nandelstadh P. van. Evaluation of hazards in CO, laser welding and related processes, Ann Occup Hyg, 2 (1992) 183-188 3 Green, J.M. Design consideration for laser guards. In Procerdinqs qf SecondEUREKA Industrial Laser Safety Forum ‘93, Coventry UK (1993) 161-167 4 Edwards, S.A., Bandle, A.M. Risk analysis as applied to high average power industrial laser systems. In Lasers in Manufacturing, Proceedings of the Fourth International Conference, Birmingham, edited by W.M. Steen (1987) 139 I52 5 Bandle, A.M., Holyoak, B. Laser incidents. In Mediurl Laser Safety: edited by H. Moseley and J.K. Haywood, Institute of Physical Sciences in Medicine, Report no. 48 (1987) 47- 57 6 Brusl, H. Typical risk situations when working with laser
7
X
9
IO
II
light-results of an analysis of accident statistics. In International Colloquium on the Safety in the Application of Laser Equipment in Research, Industry and Medicine. ISSA, Xi An, China (1991) 95-103 Frevel, A., Stelfensen, B., Vassie, L. Safe laser application requires more than laser safety. In Proceedings of Second EUREKA Industrial Laser Safety Forum ‘93, Coventry UK (1993) 2833295 Schneider, W., Heim, H. and Katzmann, H. Entwicklung und erfolgsvergleich von Massnahmen zur Beinflussung des Sicherheitsbewusstseins im Betrieb. Forschungsbericht Nr. 114, Bundesanstalt fiir Arbeitschutz und Unfallforschung, Dortmund (1974) Chaffin, D.B., Callay, L.S., Woolley, C.B., Kucienba, S.R. An evaluation of the effect of a training program on worker lifting postures, Ini J Industrial Ergonomics, 1 (I 986) 1127-l 136 Sulzer-Azaroff, B. The modification of occupational safety behavior. J Occupational Accidents, 9 (1987) 177 197 Saari, J. The effect of positive feedback on industrial housekeeping and accidents; a long-term study at a shipyard. In/ .I Indusirial Ergonomics, 4 (1989) 201~ 2 11
Optics & Laser Technology
Optics
30
& Laser Technology Vol 27 No 1 1995
of
T. J;iRVINEN
A safety survey of seven industrial CO2 lasers was carried out in order to discover the hazards, the incidents which have occurred, and perceived safety risks. A safety behaviour modification programme was developed and implemented in one laser workshop. Beam related incidents were not as rare as was expected on the basis of earlier analyses and reported accidents. Most incidents, however, related to the materials handling in the workstation. The performance feedback improved safety behaviour effectively. The baseline safety level was 50%, and during the feedback it rose up to 90%, while two months after the feedback it was 72%. KEYWORDS:
laser safety, risks, performance
Introduction There are safety and health risks connected with the laser beam that traditional technology lacks. The invisible beam can not only process metals but can also burn skin, damage the eye and cause fire. For example, an unfocused raw beam of a typical 1.5 kW laser is dangerously effective up to a distance of more than 100 m. A focused and reflected beam diffuses more quickly, but is still effective up to 10 m from the lens’. A beam reflecting from a glossy surface burns skin into blisters and, for example, sets cotton on fire in less than a second. Except for invisible infra-red light, ultra-violet and wide-band light radiation generated when processing with the CO, lasers, the radiation density may exceed the safe recommended maximum radiation doses even at distances of 1 m from the workpiece’. Laser safety standards are aimed especially at preventing the escape of beams. The beam may escape for a number of reasons: there is a dirty surface (mirror, lens) in the beam delivery system; there is mechanical or heat damage in the delivery system; there is an error function in the software or other control system, human error in maintenance, and a defective or missing workpiece3. With fault tree
HL is at The Finnish Institute of Occupational Health, Laajaniityntie 1, FIN-01 620 Vantaa, Finland. TJ is at Lappeenranta University of Technology, Box 20, FIN-53851 Lappeenranta, Flnland. Received 13 April 1994.
0030-3992/95/$10.00 Optics & Laser Technology Vol 27 No 1 1995
@ 1995
feedback,
lasers (CO,)
analysis, it has been calculated that the escape probability per laser unit is 1 x 10m2 - 1 x 10m3; in other words one occurrence per hundred years, at the most4. One can only guess the number of accidents related to the use of lasers. In the reported couple of hundred cases, the majority of accidents have involved eye injuries, most of which were caused by lasers other than the CO, laser. In addition, at least four deaths caused by electric shock were reported ten years ago’. In practice, the number of beam incidents seems to be much higher, with most of the incidents not reported2,6. The users of CO, lasers do not subjectively consider the beam as a great hazard, neither do they usually use safety goggles during normal processing’. It is no wonder, that negligence in using goggles is often mentioned in laser accident reports. Safety training for new laser operators and updated training programmes for all personnel are recommended to minimize human errors. The effect of safety training for laser personnel has not been studied, however. Studies in some other fields of safety show that training and giving information alone has no (or only minimal) effect on performance 8-9. In changing behaviour, good results have been achieved by giving positive feedback (reinforcement) of desired, safe behaviour. A positive reinforcement can modify behaviour; for instance, the use of personal protective devices, the use of safety equipment, working postures, using working tools, driving a forklift truck and industrial housekeeping’“~’ ‘. Elsevier
Science.
All rights
reserved
25
Accident
risks and the effect of performance
feedback:
The aim of this study was to survey the safety situation in Finnish laser workshops. In particular, the main focus was to find out which kinds of laser accidents and incidents have occurred. These results were compared with earlier analyses in the laser laboratory of Lappeenranta University of Technology (LUT)‘. The question was whether the same risks exist in industrial laser workshops, and also whether there are some additional risks that are different from the laboratory use of the laser. A secondary aim was to study the subjective risk assessment and safety behaviour of laser operators, while it was also desired to develop and test a safety programme for laser workshops, based on the principles of positive feedback. Material Target
and
methods
enterprises
and lasers
The analyses were carried out in three laser workshops and an Adult Training Centre (ATC). In all, five CO, lasers were analysed. The three workshops mainly subcontracted laser processing, mostly metal cutting. The number of the workers in the workshops varied from two to six. The ATC used lasers for teaching laser users. but it also leased a laser for production use. The results were compared with the earlier analyses of two lasers in LUT, which are used for research (Table I). The lasers analysed represented a wide range of laser producers, there were German, English, Swiss, American and Japanese devices. Their powers varied from 0.85 kW to 2.5 kW. In one case, the workstation was based on a stable beam and a mobile workpiece. while in all the others the situation was reversed. Methods
H Laitinen and T. Jarvinen particularly asked whether the near accidents and hazards found in the LUT laboratory were also relevant in each workshop. Interviews and group works were carried out to discover the incidents and perceived problems in laser workshops. Technical and organizational improvements were also developed in group works. All the group works lasted about l-l.5 hours. The agenda for each group work was as follows: (1) everybody generated ideas independently; (2) the ideas were presented; (3) additional ideas were generated; (4) the additional ideas were presented; (5) there was voting for the most important ideas (only one ‘own idea’ could be voted for) and (6) the ideas were grouped in order of importance. In the Adult Training Centre two laser teachers and a class of laser students took part in the group work. In Workshop 2 and Workshop 3 all the laser personnel participated. An experiment to develop the laser safety behaviour programme was carried out in Workshop 2. A group work involving all personnel was used to set the performance targets. The checklist for measuring the performance was prepared by the researchers, who also carried out all the observations. The number of items in the checklist was 89. Each item observed was marked as being either correct or incorrect (the third alternative was ‘not observed’, if the item temporarily could not be observed). The result was calculated as a performance index, which was the percentage of items observed to be correct from all items observed. To measure the baseline. four observation tours were done without any feedback. After that, a large index chart was posted on the wall with the results of baseline observations. The observations were performed once or twice a week and the new results were marked on the chart immediately. Results
In LUT. a hazard and operability study of the beam delivery system, and work safety analyses of cutting, welding and alloying. were carried out. The staff was also interviewed, and they reported near accidents with a report form (Table 2). Observations and informal interviews were carried in the laser workshops. In interviews it was Table 1. Target
enterprises
and their
out
Near accidents Laser beams had caused near accidents and problems in all enterprises (Table 3). The most common incidents
involved
slight damage
to the workstation
due to the reflected beam. Finger injuries caused by the straight beam, and potentially severe accidental starting of the laser beams had also occurred.
laser devices
Enterprise
Laser
Workstation
Use of the laser
LUT
Conrol Laser CLL 2500, 2.5 kW Rofin Sinar RS6000, 6 kW Coherent Everlaser S 48 0.82 kW Bylas BL 1500, 1.5 kW Mazak L32 1.5 kW Trumpf TLF 2000, 2 kW Photon sources P2500 2.5 kW
Control Laser, 2500 x 3500, Linear Station, 1500 ASEA 1 FIB2000 Robot station Trumpf-sheet workstation: Stable beam - mobile sheet Bylas 1500 x 3000 Mazak 1225, 1250 x 2500 Trumatic L3003, 1500 x 1000 Laser Work LW 2000 x 6000
2D and 3D cutting, welding and surface treatment; research and training 2D cutting in two shifts, 1 worker / shift 2D cutting, 3 workers 2D and 3D cutting and welding, 6 workers 2D and 3D cutting and welding; training of designers and users, operating time is leased to enterprises
Workshop
1
Workshop Workshop
2 3
Adult Training Centre (ATC)
Optics & Laser 26
Technology
Vol 27 No 1 1995
Accident
Table
2. The methods
risks and the effect
of performance
feedback:
H. Laitinen
and T. Jirvinen
of the study
Methods
LUT
ATC
Workshop
1
Workshop
2
Workshop
3
Analyses HAZOP of the beam delivery system Work Safety Analysis Near accident reporting form Interviews Problem and incident analysis, group work
Planning l
group
technical
l l l
X
X
X X
X
X
X
X
X
X
X
X
X
X
measures
work
Laser safety l
X
performance
programme
setting performance targets, group work preparing a check list for observations measuring the base line giving feedback
In all the laser workshops, the beam was reflected back to the mirror system and the resonator when trying to cut copper, aluminium or brass. The beam is reflected back if it does not pierce the sheet quickly enough. This leads to damage to the resonator mirror. Either splashes of molten metal or the reflected beam had caused small fires in the workstation, thus damaging the equipment. The relay of the temperature controller of the resonator oven was stuck twice and caused overheating of the oven. Staff noticed all the fire incidents in time and used extinguishers to prevent a fire. In some cases, the focusing lenses were worn out, which eventually melted and vaporized the lenses. With one of the lasers, the maintenance man had received an electric shock when servicing the resonator. Although he was said to have been quiet that day, there were no other more serious consequences.
Table Type
Many near accidents and problems connected with workstations had occurred. With all l.he workstations using a stable workpiece and a mobile beam, the vertical turning of the cut-off workpieces was a problem. The cut-off workpieces often turned into the upright position and so caused a risk of a collision between the cutting head and the workpiece. When this problem occurred, the worker had to stop cutting and remove the workpiece. This often required stepping on the worktable, which may have led to accidents. In order not to interrupt production. cuttmg was sometimes left on while removing the workpiece, and there was the risk of becoming crushed between the automatically moving parts. This type of near accident had also occurred. The handling of the sheet was automated at one workstation, where the beam was stable and the workpiece moved. Due to the automation, the laser
3. Laser incidents of incident
Number LUT
Beam related l l l l l l
l
related
Materials handling related incidents the cut piece of the sheet turns into an upright
l
workshops
near accident when from the workstation, near accident while
Optics & Laser Technology Vol 27 No 1 1995
8 10 3
1
1 severa I 1 2 4 1
incidents
electric shock to the service man overheating the resonator oven due to the fault in the relay
l l
ATC and three
incidents
focused beam burns finger, hair, or safety mask reflections burn tracks to the equipment in workstation accidental start-up of the beam small fire caused by the reflections or splashes of molten metal in the workstation the beam reflects back to the resonator explosion or vaporization of the lens
Resonator l
of incidents
position the user is removing the workpiece while the machine runs lifting or moving the sheet
1
2
daily incident several several
27
Accident
risks and the effect of performance
feedback:
could function for long periods of time, even without personnel. However, some disturbances occurred. Sometimes, the cut workpiece got stuck in the sheet, and the worker had to release it. On one of these occasions, the automatically closed hatch had squeezed the hand of the worker, and if the sheet had started to move, it might have severed the hand. Fortunately. another worker, who happened to be in the same room, stopped the machine.
Subjective
risk assessment
The largest safety problems were how to handle the sheets safely and without scratching them, and also how to remove the workpieces from the workstation. Suction cup lifters, for example, were considered hazardous, especially for lifting the remnant sheet after cutting. In addition, the case when a piece of sheet had turned into the upright position, such that the worker had to step on the worktable to remove it, was a problem (Tables 4 and 5).
H. Laitinen and T. Jtirvinen Table 5. The perceived the Workshop 3 Occupational problems
I. High voltage parts in the resonator 2. Sheet handling manually and with the sucker cup lifter 3. Removing the cut workpiece while the machine runs 4. Risks during adjustment of the beam 5. Air impurities 6. Splashes of molten metal 7. Reflection of the beam when cutting Al, Cu and MS
The following Technical
safety
technical
in
1. Handling of sheets (lifts and transportation) safely and without scratching them 2. Marking and packing the completed workpieces 3. Adjustment times, should be shortened by better planning 4. Keeping tools and materials in order 5. Lacking documentation of disturbances 6. Allocation of the work between separate lasers 7. Cleaning when the shift finishes
measures
were implemented:
improvements
Nine improvements were developed Workshop 3, five of them had been nine months after the group work. improvements were developed and
priority
Workshop
Adult
2
tool chests for necessary tools; containers for waste pieces of sheet; new lifting and moving equipment for sheets; repair of the exhaust ventilation; new personal protective devices (safety masks); a guide for new laser users (ATC).
by the group in implemented In the ATC, seven six implemented.
Table 4. The perceived the work
of problems
in Effects
Training
Centre
(ATC) I. Ventilation 2. Problems in handling of sheet and workpiece 3. Wear and tear of safety devices and other laser equipment 4. Lacking documentation of maintenance and disturbances 5. Adjustment of the laser, when the shift changes 6. Problems in finding tools, spare parts and documents 7. Failure to user personal protective devices
Lack of easy instructions for the beginner Lack of information of correct processing parameters and cutting gas for different materials Lack of instructions for disturbance removal Difficult procedure for teach-in programming Problems in sheet handling Risk of the cutting head bumping into the upright turned piece of sheet Removing the cut workpiece while the machine runs
of the performance
The performance follows:
targets
feedback
in the Workshop
2 were as
(1) return the tools after use to their own places; (2) put the left-over pieces and scraps in their own places; put the spare parts in their own places; keep documents and disks in order; keep workplaces clean; use the personal protective devices, when needed; set the laser controllers into the normal position when the operator stops working; actions and (8) keep a record book of maintenance disturbances. (3) (4) (5) (6) (7)
The baseline performance measurements indicated that the performance level was very constant, slightly below 50% (Fig. 1). The overall index started to rise immediately after the feedback. The average index was 80% during the 13 weeks of feedback. The increase was highly significant when tested with the chi-square test using the frequencies of ‘correct’ and ‘incorrect’ observations (p = 7 x 10-40). When the feedback was discontinued, the average index of the follow-up
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of problems
Problems with the fluency of work
safety
Inefficient ventilation, air impurities and electric hazards were also problematic. Laser users also felt that the documentation of disturbances and maintenance was not being done as it should be and that the tools and materials should be kept in better order.
priority
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Accident 100
-
90
.-
80
.-
risks and the effect of performance
0
follow-up
:
:
:
:
:
:
:
.
:
:
:
f
2
4
6
R
10
12
14
16
I8
20
22
24
week
Fig
H. Laitinen and T. Jtirvinen
The removal of air impurities worked well in a stable beam workstation, and also when the workstation was totally enclosed, but only if the doors and covers were closed. Otherwise air impurities were considered a problem. The target ventilation systems are being studied and developed in the EU-643 project.
feedback
07
feedback:
1 The performance
index
in laser Workshop
2
observations was 74X-significantly higher than the baseline (p = 1 x lo- “). One reason for the slight decrease from the highest level was the installation of one new machine in the laser room during the follow-up period. Discussion Laser beams had caused incidents and problems in all the target laser workshops. The incidents covered all the escape possibilities of the beam-which Green3 has listed. The number of near accidents exceeded the probabilities that have been calculated with fault tree analysis4 approximately a hundred times. The reason for this may be underestimating or ignoring the significance of human factors in the fault tree analysis. It was surprising that, despite the risk situations, the hazards of the beam were not considered a significant problem in any of the enterprises. In particular, the reflected beam was not even considered dangerous to the eyes. This was probably why safety goggles were not used when cutting (except in the Adult Training Centre). The same observation has also been made in Germany7. The fact that the beam is considered harmless, may be partly due to the information given by the manufacturers, who emphasize that the infra-red ray of a CO, laser is harmless to the eyes compared with other lasers. However, when it comes to high power lasers. this statement is misleading. Either splashes of molten metal or the reflected beam had caused small fires in a workstation and damaged the equipment. This indicated that materials that are too flammable are used in workstation construction. The component faults of the laser itself can also cause fire hazards. The service work and documentation of disturbances was considered a problem in the workshops; nothing was done to rectify the situation. In the laser workshops, problems in material handling from the point of view of occupational safety and the smooth flow of the work were emphasized. In every workshop there were problems with the workpieces, which had been cut from the sheet. Little workpieces often turned into an upright position, and this was the biggest single problem connected with the workstation. Trials were carried out to form a better lamella construction under the sheet but with limited results.
Optics & Laser Technology Vol 27 No 1 1995
Noise was not considered a problem in any of the places of employment within this survey. Compared with a conventional machine workshop the laser halls were very quiet. Thus, the laser for its part solves the problem of noise, which is one of the major problems of occupational safety in machine workshops.
The feedback improved performance effectively, as it has done in earlier studies”. It is obvious that the feedback procedure was the agent for change, and no other contributing factors were simultaneously present. The feedback programme is a promising tool for laser workshops in improving the safety behaviour, maintenance performance and industrial housekeeping. Problems in these areas are known to cause accidents, production disturbances, material damage, quality problems, waste of time, and dissatisfaction among workers. Better performance should simultaneously improve the safety and productivity.
Conclusions The following this study.
conclusions
are made on the basis of
(1) A proper enclosure
of the workstation can solve several safety problems effectively: the reflections of the beam are stopped by the enclosure; air impurities are contained and the local ventilation can be cheaply solved; the enclosure can be fire protected by automatic fire extinguishers. (2) The worktable should be improved so that there is no possibility of the workpiece turning into an upright position. (3) An effective machine would also require better planning and mechanization in sheet handling. Materials handling has not been sufficiently taken into consideration in the research of laser safety, nor has it been dealt with in the EU-643 project. (4) The training of laser users has been mainly organized by the manufacturers and import companies. This is insufficient when it comes to safety. The dangers of reflections are underrated and there is little information about air impurities. Training materials for laser users are needed. The hazards of the beam and reflections, as well as the hazards of air impurities have to be presented simply and dependably. (5) More studies should be carried out to standardize and test the laser safety performance feedback programme for laser workshops. The behaviour modification approach should be covered in the syllabus of laser safety officer courses.
29
Accident
risks and the effect of performance
feedback:
H. Laitinen and T. Jarvinen
References 1 Rockwell, R. James, Jr., Moss, C.E. Optical radiation hazards of laser welding processes. Part II: CO, laser, Am Ind Hyg Assoc J W(8) (1989) 419427 2 Hietanen, M., Honkasalo, A., Laitinen, H., Lindroos, L., Welling, 1. and Nandelstadh P. van. Evaluation of hazards in CO, laser welding and related processes, Ann Occup Hyg, 2 (1992) 183-188 3 Green, J.M. Design consideration for laser guards. In Procerdinqs qf SecondEUREKA Industrial Laser Safety Forum ‘93, Coventry UK (1993) 161-167 4 Edwards, S.A., Bandle, A.M. Risk analysis as applied to high average power industrial laser systems. In Lasers in Manufacturing, Proceedings of the Fourth International Conference, Birmingham, edited by W.M. Steen (1987) 139 I52 5 Bandle, A.M., Holyoak, B. Laser incidents. In Mediurl Laser Safety: edited by H. Moseley and J.K. Haywood, Institute of Physical Sciences in Medicine, Report no. 48 (1987) 47- 57 6 Brusl, H. Typical risk situations when working with laser
7
X
9
IO
II
light-results of an analysis of accident statistics. In International Colloquium on the Safety in the Application of Laser Equipment in Research, Industry and Medicine. ISSA, Xi An, China (1991) 95-103 Frevel, A., Stelfensen, B., Vassie, L. Safe laser application requires more than laser safety. In Proceedings of Second EUREKA Industrial Laser Safety Forum ‘93, Coventry UK (1993) 2833295 Schneider, W., Heim, H. and Katzmann, H. Entwicklung und erfolgsvergleich von Massnahmen zur Beinflussung des Sicherheitsbewusstseins im Betrieb. Forschungsbericht Nr. 114, Bundesanstalt fiir Arbeitschutz und Unfallforschung, Dortmund (1974) Chaffin, D.B., Callay, L.S., Woolley, C.B., Kucienba, S.R. An evaluation of the effect of a training program on worker lifting postures, Ini J Industrial Ergonomics, 1 (I 986) 1127-l 136 Sulzer-Azaroff, B. The modification of occupational safety behavior. J Occupational Accidents, 9 (1987) 177 197 Saari, J. The effect of positive feedback on industrial housekeeping and accidents; a long-term study at a shipyard. In/ .I Indusirial Ergonomics, 4 (1989) 201~ 2 11
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