Why does human error occur?

To come up with ways to safeguard against human error, let’s first consider the underlying reasons why human error happens.

【１】The 12 Categories of Human Error

(Reference *3)

According to Motoya Takagi (National Institute of Occupational Safety and Health), human error can be divided into the 12 categories described below.

From categories 1 through 12, are there any cases that come to mind that actually affected you personally?
Even mistakes, which tend to get lumped into the category of “careless errors,” have a variety of causes when you peer beneath the surface.
Now, let’s take a look at categories 1 through 12, sharing example cases of accidents at construction sites as we go.

Category 1　　Ignorance, Lack of Experience, Unfamiliarity

・Workers that are unaccustomed to a task do not know where the dangers of the task lie
・Even experienced workers cannot properly predict risks when engaging in a task for the first time or shortly after being assigned to a work site

On the first day on the job, one worker assisted in erecting the framework for a building without receiving training for new entrants to the site, and fell to his death along with an unsecured scaffolding board.

Category 2　　Disregard for Risk/Being Accustomed to Risk

・Engaging in unsafe behavior despite being aware of the risks and committing errors

While assembling a three-level scaffolding, one worker lost his balance and fell without a safety harness, thinking that he would be alright from such a height.

Category 3　　Lack of Attention

・Focusing on a task and losing awareness of anything else
・Being distracted and not able to focus on a task because the work changes from day to day

While doing live electric work wearing protective gear, one worker’s exposed backside came in contact with an electrically-charged section, electrocuting him.

Category 4　　Lack of Communication

・Errors occur due to safety instructions not being properly communicated
・This includes: not providing necessary safety instructions, ambiguous instructions, instructions that miss the point, failure by workers to listen to instructions, and workers not being able to comprehend the instructions.

While assembling a scaffolding near a high-voltage wire, one worker who was working on a task not related to electric work mistakenly came in contact with the high-voltage wire and was electrocuted

Category 5　　Group Flaws

・Errors occur when construction deadlines are tight and the work site as a whole takes on an atmosphere of “Deadline first, safety second.”

On a rush job, a team was overexerting themselves doing work on both the top and bottom of a scaffolding when the worker on the top accidentally dropped a tool, hitting and injuring the worker on the bottom.

Category 6　　Shortcut/Omission Instinct

・Engaging in unsafe behavior as the result of favoring efficiency and cutting out any cumbersome procedures.

On the way to the material stock yard, one worker crossed over a support beam which provided a shortcut relative to any of the safe passages, mistakenly falling.

Category 7　　Situational Behavior Instinct

・The instinct to focus your attention on a single point for an instant and act without taking in your surroundings.

While working on a stepladder, one worker leaned forward to prevent dropping a board he had in his hand and lost his balance, falling head first.

Category 8　　Panic

・When you are extremely surprised or panicked, your brain fails to function properly and you lose the ability to calmly take proper actions for safety.

While chipping concrete, one worker became panicked when he failed to successfully press the stop button on the jackhammer because of the shock-resistant gloves he was wearing, injuring the man as the jackhammer moved about on its own.

Category 9　　Misperception

・Failing to see or hear signals or instructions, misconceptions

One worker walked along a scaffolding under the mistaken impression that it had a scaffolding board where it did not, falling from the scaffolding

Category 10　Decline of Function in Middle-to-Old Age

・Working without being aware that your physical abilities have declined leads to errors

Unaware of the decline in his physical abilities, one worker continued work in which he carried heavy objects, placing strain on his lower back and leading to back pain.

Category 11　Fatigue, etc.

・People become more susceptible to making errors when they are tired
・Work under harsh conditions, such as long working hours or work under the scorching summer sun, makes workers more susceptible to fatigue.

One worker who was overcome with fatigue due to the deadline on a construction project was driving a company vehicle to return to the office from the job site when he collided head-on with a passenger vehicle at a flashing yellow light, causing injuries.

Category 12　Drops in Alertness Due to Monotonous Work, etc.

・Alertness drops when people continue monotonous, repetitive tasks, causing them to be more susceptible to making errors.

While banding together a large amount of rebar, one worker lost his balance. The floor the worker leaned back against was lined with joint bars which the worker’s leg came in contact with, injuring him.

【２】Take a look at latent causes, too

The 12 categories of human error are, in a manner of speaking, the direct causes of human error. However, there are also cases in which there are also causes (latent causes) that triggered the direct cause.

For instance, take the example of the worker crossing over the support beam that provided a shortcut relative to the safe passages and accidentally fell when heading to the material stock area. The direct cause was the shortcut/omission instinct. On top of that, upon looking into why the worker engaged in unsafe behavior due to the shortcut/omission instinct, latent causes such as having to go out of the way when using the safe passages, being in a hurry since there was no set timeframe, and the failure to set up an adequate number of safe passages due to a small safety budget became evident.

In a case such as this, safeguards such as increasing training to enhance workers’ awareness of safety with respect to direct causes of human error come to mind. With respect to the latent causes, safeguards such as reviewing where safe passages have been set up, increasing the number of workers, and increasing the safety budget are conceivable.

Focusing not only on the direct causes, but also the latent causes, allows us to uncover more effective safeguards against human error.

（Reference *３,*４,*５）