High-energy hazards and Direct Controls
Not every hazard can kill you. Work out which ones can, and make sure those have a control that still works when someone makes a mistake.
The threshold
Research summarised in Dr Matthew Hallowell's book Energy-Based Safety links the energy in a hazard to the likely severity of injury:
- Under about 500 joulesFirst-aid injuries
- About 500 to 1,500 joulesMedical treatment or lost-time injuries
- Over about 1,500 joulesSerious injuries and fatalities
Nobody needs a calculator on site. The threshold trains judgement. Crews learn which situations are almost always high-energy, and learn to question the less obvious ones, like stored pressure and stored mechanical energy.
The stuff that kills you
Hallowell's book writes STKY, Stuff That Kills You, and uses it interchangeably with high-energy hazard: joules for engineers and executives, STKY and the icons for crews. It is the list a crew should be able to name before work starts. Common high-energy situations:
- A person at height above about 1.2 metres with no guardrail or anchored fall arrest
- A suspended load, or anything heavy that can fall
- A vehicle, rail vehicle or mobile plant moving near people on foot
- Electrical contact at 50 volts or more, including overhead lines
- An unsupported trench deeper than about 1.5 metres
- High-pressure hydraulic, pneumatic or steam lines
- Rotating or pinching machinery with guards removed
- Hot materials, flammable vapours, toxic gases
Most sites have several at once.
These match the critical risks many New Zealand and Australian organisations already list: struck by mobile plant, failed lifting operations, fall from height, vehicle collision or rollover, loss of containment, contact with electricity or other hazardous energy, fire and explosion. See EBS and critical risk.
Why the threshold matters
If every hazard is treated as equal, the few that can kill compete for attention with the many that cannot. In US construction, low-severity injury rates fell steadily from 2010 to 2023 while the fatality rate stayed flat. The explanation that drove energy-based safety is that the two have different causes:
Minor injuries
- Come from low-energy events
- Ordinary controls manage them
Most serious injuries
- Come from high-energy releases
- Only a Direct Control works
In Hallowell's case analysis, whether a high-energy hazard was controlled was the strongest factor separating serious injuries from lesser ones, though not every serious injury involves high energy.
The 3Ts: is it a control at all?
- Timely
- In place before the exposure and active while the hazard is present.
- Tangible
- Physically present and observable on site. Not a policy, a plan or a training record.
- Targeted
- Designed and installed for that specific high-energy hazard.
A measure that fails any of the three is not a control.
Direct Controls: Strong and Forgiving
A Direct Control passes the 3Ts and two more tests:
- Strong
- It effectively mitigates the exposure when installed, verified and used properly.
- Forgiving
- It still works when there is unintentional human error during the work.
It acts on the energy by eliminating it, reducing it below the threshold, or isolating it.
Is a Direct Control
- A lockout with verified isolation
- Properly installed and used fall arrest
- A guardrail
Is not
- A sign
- Any control that fails the moment someone makes a mistake
Alternative Controls
Where no Direct Control is feasible, an Alternative Control system uses at least two complementary and independent error-reduction measures from more than one category:
- A physical obstacle
- Dedicated monitoring
- A visual reminder
Each still has to pass the 3Ts. Alternative Controls are not counted as a success in a control assessment, but they are required wherever a Direct Control cannot be put in place.
What the research found about controls
65 to 75%of the high-energy hazards observed at leading companies had a Direct Control, in Hallowell's research. That is the gap control assessment measures.