These human factors bulletins focus on how workers interact with their work environments. They are based on accident investigations that examine all the workplace factors that influence the decisions and actions of the workers involved in an accident. These factors help to identify the causes of an accident. Identifying these causes can help to prevent similar workplace accidents.

Don't forget to remember to lockout

This bulletin looks at one critical safety process that relies on human memory—lockout. If the unexpected energization or startup of machinery or equipment or the unexpected release of an energy source could cause injury, the energy source must be isolated and effectively controlled.

What happened?

A chip/n/canter operator left his work station for his regular break at 22:45 after waiting for confirmation that the chip/n/canter had powered down. When the operator returned to his work station at 23:00, he noticed that the control panel lights were active. He glanced up to the overhead monitor and saw that the trade-qualified millwright was inside the machine to install new knives. The chip/n/canter was not locked out. The millwright confirmed that he forgot to lock out before entering the machine.

From a human factors perspective, why did it happen?

There are three ways in which people's errors are brought to their attention. They can find out themselves through self-monitoring, something in the environment makes it clear that they have made a mistake, or the error is discovered by another person. In this incident, it was the chip/n/canter operator who alerted the millwright that he had forgotten to lock out. The human factor analysis reviewed what defenses were in place to help the millwright and others to remember to lock out.

The millwright was "blowing down" the area next to the chip/n/canter before the operator's scheduled break. He heard the chip/n/canter powering down. This audible feedback signaled that it was time for him to conduct the scheduled maintenance.

It is usual for millwrights to have the knives and tools needed for maintenance prepared and placed close to the chip/n/canter's entrance to save time. This meant that the millwright did not have to walk back through the main control centre (MCC) room to collect what he needed. The energy isolating devices for the chipping heads are on the main panel located in the MCC. To lock out the machine, a personal lock must be applied to the isolating device on the main panel.

On entry to the chip/n/canter at this mill, there is a wire mesh curtain strung across the point of entry. The millwrights draw back the curtain and then proceed into the machine. The chip deflector curtain's purpose is to deflect chips. It does not alert those entering as to the status of the machine, nor does it block access into the machine.

In order to be effective, a warning system must capture a worker's attention. On the path to and next to the chip/n/canter, there were no fixed signs to remind the millwright to lock out before entry. There were also no dynamic warnings such as visual or audible alarms that could have attracted the millwright's attention. There were no effective warnings to trigger his memory and remind him that he had not locked out.

When critical safety procedures rely on human memory, and a worker's memory fails—as human memory sometimes does—the outcome can be disastrous. The question that needs answering is: If a worker forgets, what is in the workplace system to help the worker remember?

Understanding human factors helps avoid workplace accidents

While there are company and regulatory requirements to lockout before conducting maintenance on equipment, usually the worker must remember to carry out the procedures. Without physical measures to block entry into a machine or to alert the operator to its status, the burden rests with the worker to remember and successfully lock out the machine.

However, memory is fallible. In this case, the millwright's memory failed, and he continued with his task. The curtain was an inadequate and ineffective means to alert him of his forgotten step, and there was nothing else in place to remind him.

A worker's memory should not be the primary line of defense for remembering to lockout. Job tasks that are potentially dangerous and life-threatening should not rely on human memory.

The workplace should be set up in such a way that effective engineering controls are in place to block onward progress when an error is made. Ideally, in situations where there is a severe risk of serious injury or death, something should be in place that prevents the action from continuing until the problem has been corrected.