Understanding the NFPA 70E HRC Hazard Risk Category Levels
The risk levels are from 1 to 4; HRC level 1 is low risk and HRC 4 is the highest and most dangerous risk level. Level 0 is little to no risk and Level 4 is extreme risk.
Which leads to the question what is an HRC? An HRC level is determined by the minimum amount of calories per square centimeter (ATPV or Cal/cm2). Any treated garment must pass through with a 50% probability of a 2nd or 3rd degree burn occurring, which is how the protective level of the treated clothing is determined. The higher the ATPV, the higher the HRC level attained, the greater the protection that is needed.
The following HRC level chart / table /matrix shows minimum ATPV value that must be calculated to acquire the next level of HRC and typical FR apparel used to accomplish the ATPV/HRC calculation.
| Hazard Risk Category | Common FR clothing at this level | Minimum ATPV (Cal/cm^2) |
| HRC 0 |
| 0 |
| HRC 1 | FR shirt and FR pants; Or FR coveralls; Single base layer of FR protection;
| 4 |
| HRC 2 | FR under garments (undershirt, underwear), FR shirt, and FR pants; FR under garments, FR coveralls; 2 or more layers of FR protection;
| 8 |
| HRC 3 | FR under garments (undershirt, underwear), FR shirt, FR jacket, FR pants, and FR coveralls; 2-3 or more layers of FR protection;
| 25 |
| HRC 4 | FR under garments (undershirt, underwear), FR shirt, FR jacket/coat, FR pants, and FR coveralls; FR under garments (undershirt, underwear), FR shirt, FR pants, multi-layer flash suit; 3-4 or more layers of FR protection;
| 40 |
DOES IT HELP TO LAYER PROTECTIVE CLOTHING?
It is understood that layering generally gives more protection than the sum total of the ATPV values of the individual garments being layered. However, this needs to be tested for each specific garment being layered and thus is never explicitly included in layered calculations, but it is known that layering FR clothing grants you at least some extra protection.
What is NFPA 70E?
The National Fire Protection Agency (NFPA) created NFPA 70E, a Standard for Electrical Safety in the Workplace. NFPA 70E standard was the first nationally recognized standard for electrical safety in the United States, and was the reference document used for the Electrical Safety-Related Work Practices (ESRWP) regulation (OSHA 29 CFR 1910.331 through .335). The first edition was released in 1976 at the request of OSHA to help provide consensus on electrical safety standards. As of 2007 it has been revised seven times with new editions in 2008 and 2009.
Useful Terms and Definitions
Electricity
The flow of an atoms electrons through a conductor. [energy,electrical]
Calorie
The energy required to raise one gram of water one degree Celsius at one atmosphere pressure. Second-degree burns occur at 1.2 calories per centimeter squared per second (cal/cm2). [energy]
A Cigarette lighter placed under your finger for 1 second equals roughly a 1 calorie burn.
A 100 cal/cm2 blast can reach temperatures of up to 35,000 degrees Fahrenheit in the center, and 11,000 degrees on the perimeter
Arc Flash
An explosive release of energy caused by an electrical arc.
An arc flash event or arc flash blast, is a type of electrical explosion that results from a low impedance connection to ground or another voltage phase also called a “short” in an electrical system. A short circuit can occur anywhere in an electrical system, usually during maintenance work when the unexpected occurs. For instance a tool dropping, a wire slipping out of your hand a mechanical accessory falling loose and so on. A dangerous arc flash can only occur if the fault current is very high – in the range 1000 amps or more. The massive energy released in the fault instantly vaporizes the metal conductors involved, blasting molten metal and expanding plasma outward with extreme force. A typical arc flash incident can be inconsequential but could conceivably easily produce a more severe explosion. The result of the violent event can cause destruction of equipment involved, fire, injury and even death, not only to the worker but also to anyone standing nearby.
Electric Arc
The passage of substantial electric current through ionized air.
Arc Rating
A value of the energy necessary to pass through any given fabric to cause with 50% probability a second or third degree burn. This value is measured in calories/cm2. The necessary Arc Rating for an article of clothing is determined by a Hazard/Risk Assessment and the resulting HRC. Usually measured in terms of ATPV or EBT.
ATPV (Arc Thermal Performance Value)
A reported value from electric arc testing. Basically, it is the measure of how much heat can be exposed to a flame resistant garment before a second degree burn injury is expected to occur.
Electronically Safe Work Condition
When the conductor or circuit part to be worked on has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.
Flame resistant/Abbreviated as FR.
The characteristic of a fabric to resist ignition and to self extinguish if ignited.
Flame retardant
A chemical substance used to impart flame resistance – not part of the basic fibers chemistry. Flame retardant treatments can diminish overtime or with use.
Flash-fire
A sudden, unexpected and intense fire caused by ignition of flammable solids, liquids, gases or dusts.
Flash Hazard
A dangerous condition caused by the release of energy from an electric arc.
Flash Hazard Analysis
A study investigating the potential exposure to arc-flash energy that a worker faces while performing a specific job task. The data collected in a Flash Hazard Analysis is used for the purpose of injury prevention and the determination of safe work practices and the appropriated levels of FR clothing and PPE.
Flash Protection Boundary
The distance from an exposed live part within which a person could receive a second-degree burn if an electrical arc were to occur.
HRC (Hazard Risk Category)
The classification of the listed task according to the type of hazard present when performing the task. Zero represents minimal risk, four represents the greatest risk.
The five Hazard/Risk categories are specified by the chart listed in NFPA 70E. The chart, based on specific job tasks, ranges from HRC 0 (which is low risk and allows for 100% untreated cotton), up to HRC 4 (which is high risk and requires FR clothing with a minimum arc rating of 40). The HRC is used to determine the necessary arc rating of a garment worn during a given job task.
- Level 0: Little to no risk
- Level 4: extreme risk
LOTO (Lockout/Tagout)
The standard contains definitive criteria for establishing an effective program for locking out or tagging out energy isolating devices and requires training for authorized and affected employees. (Contact us to schedule training for all your employees! We specialize in ARC Flash training and making sure you are OSHA compliant)
NFPA (National Fire Protection Association)
NFPA writes voluntary compliance standards related to the Fire Service and other industries. Also works directly with OSHA for establishing legal regulations for electrical safety.
NFPA 70E
OSHA bases its electrical safety mandates on NFPA 70E®: Standard for Electrical Safety in the Workplace®. OSHA evaluates compliance with its electrical safety regulations, OSHA 1910 Subpart S and OSHA 1926 Subpart K, using the comprehensive information in NFPA 70E. While OSHA tells you what to do to avoid electrical dangers, this vital Standard tells you how.
Thermal Conductivity
Rate at which heat will flow through a material.
Thermal Protection
The resistance to flame and associated thermal transfer through the garment.
TPP (Thermal Protective Performance)
A section of fabric is exposed with a combination of radiant and convective energy. The total energy required to cause second-degree burn injury to human tissue is determined based on heat transfer through the fabric specimen and the Stoll second-degree burn criteria. Single and multiple layer fabric specimens can be tested.
Hazard Risk Assessment
By OSHA standards it is up to your employer to conduct a Hazard Risk Assessment and determine the required level of protection for the tasks you will be required to perform. However, we recommend that you are aware of the information that NFPA 70E attempts to protect you from and what HRC means so that you can be confident that you are adequately protected.
When conducting a Hazard Risk Assessment the electrical equipment being tested is assessed for the the potential of an explosion or ARC flash, which is also measured in Cal/cm2. Simply stated, the goal is to always have more protection than the potential energy that could be output during an explosion or ARC flash.
