When hazards seem obvious
October 2, 2006
When a hazard seems obvious, there is a strong incentive not to worry about it. After all, our workers are smart enough to see it and avoid it. From a practical point of view, our resources can be better spent elsewhere.
A good example is a knife. We all know that knives are sharp, so knife manufacturers have no legal obligation to remove or warn about the sharpness of the cutting edge. Taking steps to educate workers about knives may seem like a waste of time. But we do provide cut-resistant gloves when the job puts workersâ€™ hands at risk. How do we decide when a hazard warrants attention?
Often, the key element is context. We need to look at the specifics of the job, the environment, the workersâ€™ training and past experience, motivation and incentives. Hereâ€™s an example I was involved in recently that illustrates the importance of context. A textile worker was monitoring a roll of chemically treated fabric as it entered a pad roller that pressed the fabric at high pressure to remove the chemicals. The fabric entered the machine around waist height through a series of rollers. The entry point created a dangerous hazard because the workerâ€™s hands could be caught between the rollers and pulled into the machine, crushing the workerâ€™s arm in the process. Unfortunately, this is in fact what occurred.
The company thought the rollers were obviously dangerous and workers wouldnâ€™t put their hands too close. But my analysis identified nine contextual elements that contributed to the injury and, in combination, overwhelmed the obviousness of the hazard in protecting the worker.
Nine elements of context1 Work history: The operator had worked with similar machines in the past that did not expose him to this hazard. One had an entry point at the top, which was not accessible. Another was guarded, allowing the worker to work safely near the entry point. This history created a false impression that working with this class of machines was safe.
2 Training: When this machine was first introduced to the workplace, all of the operators were instructed by a representative from the equipment maker. One of the activities they were trained to do was to stand next to the fabric and pick off pieces of lint so they wouldnâ€™t go into the machine. The task was demonstrated by the trainer with his hands in close proximity to the entry point. It is not surprising that the operator assumed that if the trainer said to perform the task this way, it must be safe. This is true even though when he was interviewed after the accident, he admitted it looked dangerous.
3 Attention focus: The task required the operator to watch the fabric closely, and therefore left little attention to monitor his distance from the entry point of the machine. Over the course of his shift, natural variation and postural sway caused him to be unknowingly close to the entry point.
4 Workplace layout: The distance between the pad machine and the drum from which the fabric was taken determined how much time the operator had to see the lint and remove it. The distance between this location and the roller entry point hazard, combined with the average speed of the fabric, provided approximately one second from the point where he could grab the cotton before his hand would be caught by the rollers. One second is very little time for a worker to inspect the fabric, remove any observed lint, and pull away his hand.
5 Materials: The fabric that was being processed at the time of the incident was made of a material that had more friction than the operator anticipated, based on past experience. As he grabbed cotton from the surface, there was a greater probability than he expected that it could pull his hand towards the entry point, requiring a higher force than usual to pull his hand away.
6 Machine design: The speed at which the fabric moved varied considerably because the drum was situated on a platform that rotated periodically as the fabric was removed. This created a wide variation in the time available to remove lint that the operator observed on the fabric. If he grabbed the fabric just as the platform rotated, he would have had much less time to pull his hand out of the way before it contacted the entry point. This lead time was hard to predict.
7 Peer behavior: All of the workers operating this and similar machines worked near the entry point in the same way. Many of them suspected that the task was dangerous, but all continued to work as instructed. Workers develop confidence in their behavior as a result of observing their peers working the same way.
8 Shift: The operator worked 12-hour overnight shifts. Physical fatigue would have increased the sway in his standing posture. There would be many occasions in which his body was in close proximity to the entry point. Mental fatigue would also decrease the likelihood that he realized he was close to the entry point and decrease his reaction time if and when he did notice.
9 Warnings: There were warnings placed on the machine regarding the entry point hazard. However they were not designed according to ANSI standard Z535.4 Product Safety Signs and Labels. In particular, they contained the signal word â€œCaution,â€ suggesting that the hazard was not serious. Also, they were in English, which the worker did not speak very well.
Itâ€™s understandable to consider the entry point hazard of this textile machine â€œopen and obvious,â€ to use the legal term that protects equipment manufacturers from liability lawsuits. The rollers are openly visible and anyone can see that it would crush oneâ€™s fingers. However, in the context in which this operator worked, there were many factors that eliminated the protection provided by this obviousness. When deciding what hazards to focus our safety efforts on, it is important to consider these contextual issues.