The fallacy of the cracked helmet

We tend to look at a cracked helmet and assume it is “proof” it saved a life.
Actually, a cracked helmet has failed to work as intended:

“The next time you see a broken helmet, suspend belief and do the most basic check – disregard the breakages and look to see if what’s left of the styrofoam has compressed. If it hasn’t  you can be reasonably sure that it hasn’t saved anyone’s life.“

Polystyrene-based helmets protect by absorbing the energy of the impact through compressing the polystyrene. In a serious accident, polystyrene helmets tend to break into pieces. If the polystyrene has broken into pieces but not compressed, it has failed to work as intended.

soft-shell-helmet A bicycle helmet is a piece of polystyrene covered by a thin layer of plastic.
Notice how the helmet has cracked, but the polystyrene did not compress.
This indicates the helmet failed to absorb the energy of the impact.

We have a tendency to attribute causality from the timing of events. If we have a fall with a helmet, then notice that the helmet is cracked and we do not have a head injury, we tend to attribute the lack of head injury to the helmet. However, cyclists fall with and without helmets, and rarely get a serious head injury in either case.

Protection is good, except when it increases the risk of accident

Helmets can have unexpected side-effects. One surprising observation has been an increased risk of accidents. After a helmet law was introduced in Australia, cycling injuries tripled:

cycling_inury_rate_following_helmet_law_2

 After the helmet law was introduced in NSW, Australia, the risk of injury tripled.
Many of those additional injuries would have been “cracked helmet” scenarios.

How can the widespread wearing of helmets increase the risk of injuries? There is a well-known safety phenomenon called “risk compensation“, following observations that as people feel safer, they tend to take more risks. More risks means more accidents, particularly when people are lured into a false sense of safety.

Sometimes our intuition can be wrong

It is easy to forget that bicycle helmets are only designed to protect in minor impacts:

“In cases of high impact, such as most crashes that involve a motor vehicle, the initial forces absorbed by a cycle helmet before breaking are only a small part of the total force and the protection provided by a helmet is likely to be minimal in this context. In cases where serious injury is likely, the impact energy potentials are commonly of a level that would overwhelm even Grand Prix motor racing helmets. Cycle helmets provide best protection in situations involving simple, low-speed falls with no other party involved. They are unlikely to offer adequate protection in life-threatening situations.“

Dr Carwyn Hooper from St George’s University in London reports:

“Looking at evidence, it does not matter if people are wearing a helmet or not, any serious accident on a bike is likely to kill them”

Helmets increase the volume of the head, thus the chance of the head hitting the ground in an accident. Helmets also increase the risk of neck injuries, and can aggravate brain injuries. There is no guarantee that a fall with a helmet will result in less severe head, neck or brain injuries.

It is natural to assume a helmet saved us. However that doesn’t mean it is true. We don’t know what would have happened without it. Cyclists, with and without helmets, get hit by cars; the survival rates are identical. Most bicycle accidents do not result in serious head injuries, with or without helmets. We tend to overlook this, and eagerly attribute a lack of head injury to the helmet:

“see the double-standard of finding it entirely logical when helmeted cyclists who survive collisions report that wearing a helmet saved their life. It is a powerful emotional argument, but logically, statistically, and scientifically, it is erroneous for the same reasons it would be erroneous to say that not wearing a helmet saved Gene Hackman’s life. If a cyclist wears a helmet and they emerge from a collision alive, that implies correlation, not causation.”

Helmets can be deceptive

Surprisingly, wearing a helmet can increase the risk of accident and injury. Cycling is a safe activity. Statistically, we can expect a severe head injury once every 8,000 years of average cycling. Wearing a device that increases the risk of accidents may not be the most effective way to enhance safety.

A cracked helmet may indicate a cyclist not riding cautiously enough, perhaps lured into a false sense of safety. It is ironic that a cracked helmet is hailed as “proof” that it saved a life, while the accident may not have happened without it.

It is easy to be mislead, especially after a traumatic experience. It is important to be realistic about helmets capabilities, and to base that assessment on facts. Overestimating their protection can be dangerous. After a serious accident, it is too late to discover that bicycle helmets are not designed to protect in a serious impact.

Bicycle helmets can be insidious:

  1. Initially, they seem to protect.
  2. However, they tend to increase the risk of accidents.
  3. They are unlikely to offer adequate protection in a serious accident.

Does the protection compensate for additional accidents?

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