How does safety work? That is, given a hazardous situation, how do we prevent injury from that situation? At first, these questions seem far too abstract to even begin to formulate an answer. So, let’s consider some real situations.
Consider a pot of boiling water on the stove. Clearly, if we were to touch the pot or the water, we would incur a burn. So, we don’t touch the pot, and we don’t put a finger in the water.
Consider similar situations where we are careful to avoid the hazardous situation. Consider the process of crossing a street. We avoid crossing in front of a nearby moving car. Consider the Chernobyl nuclear power plant disaster. We avoid getting within 20 miles of that site.
We simply stay away from the hot pot, the boiling water, the moving car, and the radiation-emitting power plant. We interpose distance between us and the hazardous situation. In some cases, that distance is small as in avoiding a burn from a pot of boiling water. In other cases, the distance is large as in avoiding the radiation from Chernobyl.
And, we avoid putting a finger into an empty Edison-base light socket.
So, one means of protection against injury is personal avoidance. Personal avoidance is usually accomplished by putting distance between us and the hazardous situation.
How much distance?
That depends on the nature of the situation. If we are considering the pot of boiling water, then the distance need only be a few inches. If we are considering glass-making, then the distance from the furnace needs to be quite a few feet. In these two cases, the distance can be predicted from the fall-off of heat and temperature with distance.
If we are considering crossing the street, then we do some mental vector analysis of our velocity and the moving car velocity. Again, we could predict the distance through vector analysis.
If we are considering the Chernobyl incident, then we can consider high-altitude winds to predict the direction and distance of wind-born fall-out.
If we consider the Edison-base light socket, then the distance can be very small, provided we don’t actually touch the metal conductors.
What does this have to do with product safety?
One way in which safety works is by personal avoidance. Individually, we make personal avoidance work by interposing sufficient distance between us and the hazardous situation.
Now, let’s consider that we want to pick up the pot of boiling water. To do so, we commonly use a “hot pad” or “mit” or some thing between our hand and the pot. This “thing” prevents the pot from burning our hand.
Consider also that, in the summer, to avoid sunburn, we anoint our body with a lotion which prevents the hazardous sun rays from reaching the skin.
Or, at Chernobyl, the workers dress in protective clothing that prevents the nuclear energy from reaching the body.
So, another way in which safety works is by personally interposing some device which attenuates or deflects the energy before it reaches the body. For the purposes of this discussion, such devices, e.g., the hot pad, the sunburn-preventing lotion, and the protective clothing are personal safeguards.
A safeguard is a protective device interposed between the hazardous situation and the body. It is a personal safeguard because it is attached to the body.
Individually, we make personal safeguards work by interposing them between us and the hazardous situation.
We have discussed two means of safety, personal avoidance and personal safeguards.
Note the use of the word “personal.” Such safeguards are effective only if we know when and how to use them.
In most cases, someone will need to tell us when one is needed, and sometimes how to use it. For the hot-pad, we probably learned from our parents. For the sunburn-preventing lotion, the instructions on the label tell us these things.
Note that for both personal avoidance and personal safeguards, safety is accomplished by interposing something, either distance or a device, between the hazardous situation and the body.
We said that a safeguard is a protective device interposed between the hazardous situation and the body. If we attach that safeguard to the equipment or product, we now have an equipment safeguard.
Note that an equipment safeguard works just as a personal safeguard except that instead of being attached to the body, it is attached to the equipment.
For example, the equipment enclosure commonly provides protection against electric shock. It is interposed between the hazardous situation and the body. But, it is attached to the equipment.
There is a big difference between personal safeguards and equipment safeguards.
A personal safeguard is only effective if the individual chooses to use it, and uses it in accordance with instructions.
On the other hand, equipment safeguards are independent of the person using the equipment. The only caveat is that the safeguard must be sufficiently robust to withstand normal use of the equipment for the lifetime of the equipment. (Sometimes, the safeguard must be sufficiently robust to withstand abnormal use.)
A manufacturer controls equipment safeguards. He cannot control personal safeguards or even personal avoidance.
However, every manufacturer at various times does attempt to invoke personal avoidance and personal safeguards through the use of warnings. A warning is an instruction to either avoid a situation, or to employ a personal safeguard. Therefore, a manufacturer should understand that use of a warning is a poor substitute for an equipment safeguard.
I have described three models for protection against injury, personal avoidance, personal safeguard, and equipment safeguard.
Each is used every day by each one of us.
Safety is accomplished by interposing a safeguard between the hazardous situation and the body.
An equipment manufacturer cannot control
safety by means of personal avoidance or personal safeguards. Therefore, his only avenue for making safe products is to provide equipment safeguards for every hazardous situation.
Copyright 1996 by Richard Nute Originally published in the Product Safety Newsletter, Vol. 9, No. 2, April – June, 1996
Richard Nute is a product safety consultant engaged in safety design, safety manufacturing, safety certification, safety standards, and forensic investigations.