Computer vision's real job isn't watching for hard hats
PPE detection is the easy, low-value use of vision. Struck-by events are among the incidents that actually kill people, and that is where vision has to prove it can see a person in the line of fire.
Walk any site running a vision pilot and you’ll find the cameras doing the same thing: flagging people without hard hats or vests. It demos well and scores easily, the object is either on the head or it isn’t. But when did a missing hard hat last kill someone on your site? PPE non-compliance is real, but it’s rarely the mechanism of a fatality. The mechanism is a person and a moving mass occupying the same space.
The value is in the line of fire
NIOSH’s work on struck-by hazards is blunt about where the deaths come from: contact between a worker and an object or equipment, with transportation incidents alone a large share of fatal struck-by injuries in construction (NIOSH struck-by resources). The contributing factors are spatial and perceptual, blind spots, noise, degraded awareness, exactly the conditions a well-placed camera could read that a human operator cannot. NIOSH frames collision prevention as two steps: early detection of risky proximity, then action to prevent contact. Detection is the part vision could own. That reframes the question from “is the PPE on” to proximity, exclusion-zone violation, and trajectory, is a person in the swing radius, the back-up path, the cone where the load is heading. This is what the ANSI/ASSP A10 construction series exists to control, and it’s the harder engineering problem: real distance and motion from a 2D image, in dust and glare, with false alarms low enough that operators don’t switch it off.
The test
For any vision deployment, ask: would this system have raised an alarm before your last serious incident, and would it have arrived early enough to act on? If the tool only detects PPE state, the honest answer is no, it was never watching the hazard that hurt people.
Measure a deployment against the incidents in your own OSHA logs, not detection accuracy on a benchmark unrelated to your fatalities. Green hard-hat metrics can coexist with a site where the real exposure, people in the path of moving equipment, is never observed at all.