“Can’t Rather than Don’t” — A Universal Safety Principle

The phrase “can’t rather than don’t” encompasses a universal safety principle. “Don’t” requires comprehensive vigilance, conformance to rules and regulations, and other forms of human intervention, such as inspections and preventive maintenance. Traffic safety relies almost entirely on don’t, as in “don’t run stop signs or traffic lights” and “don’t change lanes without looking first." Conformance requires constant vigilance and attention from the driver. Stop lights behind tree branches, stop signs that have faded to white octagons, worn lane markings, and potholes represent failures of the “don’t” approach.
A punch press that can easily crush or sever a worker’s hand is an application for “can’t rather than don’t.” Signs that said “Don’t put your hand in the punch press” and procedures that involved signals between workers failed to prevent the loss of thousands of fingers and hands in American workplaces. The Ford Motor Co. designed punch presses to require each worker to press two buttons, one with each hand, to operate them. Instead of warning workers, “Don’t put your hand in the punch press,” the punch press was designed so the workers’ hands can’t be in the press when it closes. The accident then becomes impossible.
This article discusses inherently safer technology (IST) and inherently safer design (ISD) in terms of the “can’t rather than don’t” principle. It then shows how starting the questions in “The Five Whys” technique with “why can’t” helps to ensure personal and process safety.