Heinrich's Law

Almost everyone has tripped on a rock while walking and nearly fallen. If you catch your balance in time, you usually breathe a sigh of relief and shrug it off. Nothing was damaged, and you weren't hurt at all.

But if you look closely at accident records from workplaces, those heart-stopping moments don't just pass by at random. Heinrich looked at 330 accidents of the same kind. One ended in a serious injury, 29 ended in minor injuries, and a full 300 ended with no one hurt, just a lot of sighs of relief. In other words, behind one big accident lie many more small accidents and close calls.

This is the 1-to-29-to-300 rule, widely used in the field of safety management. A major disaster doesn't strike out of the blue like a bolt of lightning. It's the result of many small, invisible warning signs piling up and being ignored until they finally burst into the open.

When you see a thin crack in a wall or hear a strange noise from a machine, it's easy to think, "It's probably fine for now," and move on. The factory hasn't stopped and no one has been hurt, so it gets written off as a minor problem.

But leaving a hazard alone is like rolling a dangerous die over and over without ever stopping. If a close call happens hundreds of times and no one finds and fixes the cause, the odds will eventually catch up with you, and it can turn into a catastrophe that can't be undone.

So the key starting point for preventing big accidents is to find the causes in the many accidents that ended without injury (the 300 at the bottom of the pyramid) and remove them early. That said, the steps that cut down minor accidents aren't always the same as the steps that prevent major ones, so risks that could lead to serious harm need to be examined separately. Above all, it matters to build an open environment where small mistakes aren't hidden or overlooked, and where anyone can report them freely and get them fixed right away.

The numbers 1, 29, and 300 in Heinrich's Law are not an absolute formula that fits every workplace exactly. The real ratios can vary a lot depending on the kind of workplace and the tools being used. Many researchers also doubt the numbers themselves, because Heinrich never made his underlying data public.

To put it more precisely, the heart of the law isn't the exactness of the numbers. It's the statistical tendency that in many accidents, warning signs show up before the big one. If you spot a flaw that looks minor, or a small mistake, early and fix it, you can head off enormous losses and tragedy. But a low count of minor accidents doesn't mean the risk of a major one is low too. Sometimes a big accident has causes that are entirely different from those of small ones.

Today this idea has spread well beyond safety management in places like factories and construction sites. It's used to catch frequent hiccups in an online service before the servers go down, or to analyze small customer complaints so a company can avoid a major crisis.