Machine Safety: Crossing the yellow line

Yellow line theory versus complacency: On a train platform few people cross the yellow line, without any specialized training, yet, in a manufacturing environment, accidents happen regularly after people cross the yellow line and even more formidable barriers. Why?

By JB Titus September 13, 2014

The "yellow line" in manufacturing has been around for a very long time. But, a "yellow line" is frequently tested in manufacturing versus the "yellow line" on a train platform. Do people understand the "yellow line" theory differently? Both carry high potential hazard levels.

Many of us have stood on a busy train platform and witnessed crowds conforming to standing behind the yellow line (or out of the yellow zone) along the platform, where trains pull in for people to disembark from and board the train. Typically there are no signs, roving police, training, or regulations governing these high-risk areas. The crowds of people are often distracted by children, phones, newspapers, conversations, and occasionally rushing to catch a scheduled train. Yet, very few incidents occur. Let’s face it: Those who do accidentally fall over the yellow line into an oncoming train have likely purchased their last tickets. 

Compensation theory

Is this a human risk compensation theory suggesting that people typically adjust their behavior in response to the perceived level of risk?

Industry (in my opinion) has a whole different approach to the "yellow line" theory. I believe that potential known hazards in manufacturing facilities are identified in different ways, primarily via regulations, codes, standards, and company policy. Yellow lines are one way hazards are designated in industry.

Hazards behind the yellow lines in industry are perceived differently than on a train platform. For example, people have jobs running machinery behind the yellow lines along walkways and aisles in manufacturing facilities. Some people are prohibited from crossing these yellow lines, and others are permitted. Those permitted must have special training, in some cases have special personal protective equipment (PPE) protection, and in most cases be an employee with special authorization. Yet, many more incidents occur in comparison to the train platform. [subhead]

Possible answer

Perhaps this human risk compensation theory suggests that people typically adjust behavior (complacency) in response to the perceived level of risk accompanied with frequency of exposure.

These very different characteristics of human behavior need to be considered when setting safety policies. See questions below and post your comments below.

– J.B. Titus, Certified Functional Safety Expert (CFSE), writes the Control Engineering Machine Safety Blog. Edited by Mark T. Hoske, content manager, Control Engineering,


Editor questions

1) If penalties were more severe in the workplace, would there be fewer accidents? That is, if employees knew that crossing the yellow line once meant they have punched their last time clock for that employer, would that reduce risk?

2) Do employees know what infractions, would result in dismissal?

3) Safety policies; safety markings, signs, and guards; and safety technologies: The greatest of these is…?

Reply in the comments section below. has related machine safety explanations.


ASSE — Professional Safety Journal- Near-Miss Reporting, May 2013

OSHA — search for near miss

Contact: for "Solutions for Machine Safety."

– See related articles on safety culture below.