A question we’re often asked is what is the Stoll curve? It’s a fairly technical subject, but here’s a relatively non-technical explanation of the Stoll curve and how it helps protect you from Arc Flash incidents.
Explaining the Stoll Curve
The Stoll Curve was developed by Alice Mary Stoll, an American biophysicist who developed fire-resistant clothing.
It was developed as a way to predict how long pilots could tolerate G-forces during air combat. Stoll created a scale for predicting when humans would pass out based on blackening the forearms with thermal radiation.
Now used in more than just examples of flying at high altitude, the Stoll Curve is used to calculate when more protection would prevent further injury.
The curve establishes the rating of the transfer of heat energy (calories) based on the time the heat takes to transfer and the amount of heat energy produced. In an Arc Flash incident, your PPE should absorb the heat energy, which results in delaying the heat energy from reaching your body and causing injury.
The graph of the curve determines how the human body would respond to high heat for a short amount of time, and low heat for a long amount of time.
How the Stoll Curve is used in Arc Flash PPE testing
All Arc Flash PPE has to conform to IEC 61482, a set of regulations updated in 2018. When testing Arc Flash PPE, fabric is exposed to extreme heat and sophisticated equipment records how much energy passes through the material and the level of energy (energy incident) it was exposed to.
The Stoll Curve is used in testing along with a graph of heat flux exposure time. The point at which the heat flux cross the Stoll Curve is identified as the point at this a human would feel pain and be at risk of second-degree burns.
Arc Flash testing results in a Cal-rating for garments and fabric, which is defined as the incident energy level at which there is 50% probability that a person would sustain second-degree burns – the APTV rating, the level of incident energy at which the material would break open – the EBT rating.
Garments tested to the new standard are also given an ELIM rating – the rate at which there is 0% probability of a person sustaining second-degree burns.
To be sure you and your team are safe when carrying out work where there’s a risk of Arc Flash incidents, use the information from your Arc Flash study which will recommend a Cal-rating for your PPE, and ensure that everything you wear contributes to this protection.
We hope this information about what the Stoll Curve is and how helps prevent you from Arc Flash incidents has been useful – if you need advice about your own Arc Flash protection call our friendly experts on +44 (0) 1482 679600.
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