Addressing Potential Firefighting Hazards Around Photovoltaic Systems

Underwriters Laboratories publishes standard to protect firefighters from the shock hazards of damaged solar panels

ANSI/CAN/UL 3741: Standard for Safety for Photovoltaic Hazard Control, first published in December 2020, provides a means of evaluation for photovoltaic (PV) hazard control components, equipment and systems that reduce shock hazards from energized PV system equipment and circuits in a PV array. It is specifically intended to establish and expand requirements for the evaluation of a rapid-shutdown PV array that can keep firefighters out of hazardous current paths when responding to emergency situations in homes and buildings with PV systems. Because damaged PV arrays present a risk of shock to first responders, a means of PV hazard control or hazard reduction is required to provide assurance and protection. Systems that comply with UL 3741 should also decrease potential hazards for others working in and around the PV array.

In developing the Standard, UL utilized empirical data collected by its own Firefighter Safety Research Institute in a 2011 research project on the unique safety considerations and hazards presented by PV installations during fire mitigation. Additionally, in 2017, UL collaborated with Sandia National Laboratories under a US Department of Energy research project to gather additional data for the development of the Standard. The research evaluated electric shock parameters for ungrounded and grounded PV arrays, defined hazard-controlled states for PV system operation under emergency conditions, determined body impedance models and corresponding shock thresholds for male and female firefighters with PPE and tools, and harmonized safety standards and committee work. 

The Standard is nationally recognized and approved by the American National Standards Institute (ANSI) and the Standards Council of Canada (SCC), offering greater consistency in safety of photovoltaic hazard control across both countries and jurisdictions. The binational Standard eliminates the risk of de-harmonization as updates are implemented, while also allowing manufacturers to design and evaluate products for both countries.

Standards Technical Panel Membership

The Standards Technical Panel (STP) for UL 3741 is comprised of subject matter experts from firefighters’ associations, as well as representatives from the fields of hazard control equipment manufacturing and PV equipment manufacturing. Other participants represent state and federal government authorities and organizations dedicated to energy research and development.

The STP has strong binational participation with representatives from the U.S. and Canada. The development effort also received considerable support from a broad set of stakeholders. These partners provided significant time and effort, and Underwriters Laboratories is grateful for their contributions. 

The knowledge shared and questions asked by this diverse group of panel members and stakeholders is conducive to an effective and comprehensive standard thanks to the unique perspectives each participant brings to the process. 

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Fast Facts

  • The first edition of UL 3741 was published on December 8, 2020.
  • UL 3741 addresses safety principles and processes for evaluating rapid-shutdown PV arrays that can protect firefighters from shock hazards on homes and buildings with solar panels.
  • Researchers analyzed body impedance models and corresponding shock thresholds for both male and female firefighters with PPE and tools.
  • In addition to protecting firefighters, systems that comply with UL 3741 can also decrease potential hazards for others working in and around the PV array.
  • The Standard can be purchased or viewed digitally for free at ShopULstandards.com (registration required).

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