Fire Safety

What We Know

UL 9540A Testing

Tesla states the Megapack 3 is designed to meet UL 9540A, the standard fire test for battery energy storage systems. The test forces a cell into thermal runaway, then a module, then a full unit, and measures whether the fire spreads and what heat and gases come off. Fire officials use the results to set spacing and decide what protection a site needs. We will post the test report for this equipment when Tesla releases it.

Built-In Detection and Thermal Management

Every Megapack unit includes integrated fire detection and thermal management. The design relies on the cabinet itself, cell spacing and monitoring rather than on sprinklers inside the unit. Key features include:

• 24/7 thermal monitoring: sensors detect temperature anomalies in real time
• Automatic shutdown: the system isolates affected cells before conditions escalate
• Liquid cooling: active thermal management keeps batteries within safe operating ranges
• Designed not to spread: the cabinet and the spacing between units are designed to keep a failure in one unit from reaching the next. The fire protection engineering report for the earlier Megapack 2 and 2XL, in the Document Library, found no spread between units at the tested spacing. In the US record, the Megapack fires at older sites stayed within one or two units.

What the US Record Shows

Residents ask whether a battery fire would mean an evacuation. The record of US grid battery fires since 2019 is in the Slide Library (slides 41 and 42) and the Cumulative Impact Analysis. In short: at the outdoor lithium iron phosphate fires on record, nobody was asked to leave home; one closed the schools next door for a day. Every shelter or evacuation order at an outdoor unit was lifted within a day except one that ran about two days, and the multi-day orders were at batteries inside buildings. Where air was sampled at outdoor fires, hydrogen fluoride was not detected at the perimeter. That is the record, not a promise; the incident commander decides the response here.

NFPA 855 Compliance

We designed the project to meet NFPA 855 (Standard for the Installation of Stationary Energy Storage Systems). This standard covers siting, spacing, fire suppression, ventilation, and emergency response, setting clear requirements for:

• Minimum separation distances between units and property lines
• Fire department access roads and hydrant placement
• Hazardous material containment
• Ventilation to prevent gas accumulation

Emergency Response Planning

We are working directly with Charlton Fire Chief Rob Barton on a site-specific emergency response plan. This includes:

• Pre-incident planning with the fire department
• On-site familiarization visits for first responders
• Specialized training on battery storage fire response
• Clear protocols for notification and evacuation if ever needed

What We're Still Studying

• Final fire suppression system specifications: our engineers are developing detailed system specifications, which we will include in the consolidated permit application
• Mutual aid coordination: we are holding discussions with surrounding fire departments to coordinate mutual aid
• Detailed thermal runaway modeling: we will complete a site-specific analysis as part of the EFSB filing

What You Can Influence

• Emergency response priorities: tell us what matters most to you about fire safety. The August 19, 2026 Fire Safety Webinar with Jim McDowall is recorded in the Engagement Log.
• Information requests: if you have a specific safety question, submit it through Share Your Voice and we will answer it publicly
• Ask the Chief: questions for Charlton Fire about the Emergency Action Plan can go through the comment form, and we pass them on and publish the answers