August 12, 2026
What Does cal/cm² Mean for Arc Flash Safety?
September 12, 2025
When it comes to arc flash protection, one small unit of measurement makes a big difference: cal/cm² (calories per square centimeter). If you’ve ever looked at the label on an arc-rated (AR) garment, you’ve likely seen this number—but what does it really mean? Our Vice President of Technical, Scott Margolin, is here to help break it down:
Definition
Cal/cm² stands for calories per square centimeter.
- It’s a unit of incident energy commonly used in arc flash safety, and crucial in determining the protective capabilities of AR/FR clothing.
- It measures the amount of thermal energy (heat) that could be received on a surface area (like a worker’s skin) during an arc flash event.
- It’s important to understand that cal/cm² doesn’t measure the arc’s temperature — it measures heat flux. The impact of an arc flash on skin depends on both the duration of exposure (time) and the intensity of energy delivered over a given surface area.
Why It Matters
- Cal/cm² directly links the hazard level of an electrical task with the protective clothing required to keep workers safe. The higher the cal/cm² rating, the greater the protection needed.
- AR/FR clothing is tested and labeled with a cal/cm² value. This value indicates the level of thermal protection the garment provides before there is a 50% probability of causing the onset of a second-degree burn.
From Basics to Best Practices: Arc Flash Explained
Arc flash injuries among electricians remain a serious—and preventable—problem. With demand for electricians rising, so does the risk of injuries and fatalities.
In November 2024, OSHA released new guidance to strengthen arc flash safety for electricians, operators, maintenance staff, and others working near energized parts.
Whether you’re refreshing your knowledge or learning for the first time, our Fundamentals of Arc Flash series gives you the foundation you need for compliance and real protection.
