Safety and Safety Analysis

The picture above is a manually operated station where an operator places two metal parts into a fixture. When the second item is placed a sensor activates a press mechanism and the two pieces are pressed together. When evaluating an application like this a number of criteria have to be considered:

1. Is there another way to do this that doesn’t expose the operator to a hazard?
2. What is the potential seriousness of the hazard?
3. What measures can be taken to limit or eliminate the hazard?
4. What measures can be taken to warn the operator of the hazard?

In the picture above there are quite a few safety related aspects you may not have noticed. An operator can’t fit their hands easily into the press area. A sensor that detects only metal is used to actuate the press. The two sensors shown on the right side are arranged such that one must be blocked and the other clear before the press will operate; this ensures that only objects of the correct configuration will be pressed. (This is also used as a quality or poka-yoke tool as the sensor shoots through a location hole in the part).

Some of the safety related items are easier to see: the big Pinch Point warning label on the press, the yellow paint indicating caution and the smaller warnings on the laser photoeyes. There is also an E-Stop button within easy reach that will disable the station.

When evaluating the design of a machine or station typically you will use a form for hazard analysis. Various regulations and guidelines will be used as described here in my previous post. The form I use as part of my risk analysis at work rates hazards by how easy it is to avoid the hazard, how frequently the operator is exposed, how severe is the potential injury (minor, loss of an appendage or limb or fatal). It then rates the hazard by severity, exposure and avoidance to generate a risk reduction category from R1 (Severe) to R4 (Minor). Safeguard selection is then based on this and the system re-evaluated after implementation of safeguards.