Humans Make Mistakes

One frustration many of the public experience in reading about chemical plant accidents is that often the company will report: “human error was the cause.” Although this may be in part true, we must look further into what system or equipment failed to prevent the human error from escalating into an undesirable incident.

As professionals in Process Safety, we must recognize the fact that people will not always follow procedures, read the instructions, or be in the places we expect them to be. We put in place many layers of prevention activities that should minimize the impact of the human performance error. I always like to use the following graphic to show how this works.

In this case, as in real life, the “lightning” is bad for processing operations. The layers of prevention activities should be tight enough and overlap so that no holes line up, keeping the lightning from striking the plant.

So what are some techniques that can be used to ensure that we look beyond why the human failed? Is there more than “let’s fire that person and be on with business”? There are several good techniques that force the investigation team to look beyond the most obvious answer. Most of them have their background in the Department of Energy techniques used at nuclear plants.

A simple technique is to actually put yourself in the operator’s shoes. That means repeating the task or situation as it actually happened. This may require reporting in on the night shift with the same exposures to temperatures and noise. At the same time, the investigators should conduct a formal analysis of the task or instructions for criticality. This is not unlike a HAZOP study considering each step in the task or operation as a “node.” Consider the implications of making a small error in each step. They may compound a small problem or be the real underlying cause of the incident.

A good investigation protocol will have checklists and question points to ensure that the human factors have been addressed as potential causes. Some areas that should always be examined are:

The Machine Interface - labels and controls
The Environment - Lighting, noise, temperature
System Complexity - especially in moments of panic

One of the difficult things for the investigator is to overcome the tendency to say: “People have done this correctly thousands of times without making a mistake, why can’t this person?” If the person made that one mistake in 1000, and the resulting consequence was catastrophic, then one of the management systems in Process Safety failed. It’s our job to find the root cause of the human mistake and ensure that our systems are tightened so that it does not happen again.