On Saturday, July 23, 2022, at about 3:39 a.m. eastern daylight time, a battery electric transit bus (BETB), owned by the Connecticut Department of Transportation and operated by public transit system CTtransit, began emitting smoke while parked inside a CTtransit maintenance facility in Hamden, New Haven County, Connecticut. The BETB had been placed out of service 2 days earlier due to an error in the bus charging system. Responding fire department personnel did not observe any visible flames, and the bus was pushed to an outdoor, isolated parking area. In the process, two CTtransit maintenance workers suffered smoke inhalation and were treated at an area hospital. Later that same morning, the bus was again emitting smoke, and fire was observed coming from the rear of the vehicle. Fire personnel returned to the site and the incident commander decided to let the bus burn in the controlled environment. The fire remained active for several hours and fully consumed the vehicle. Following the departure of fire personnel, the bus continued to smolder while remaining isolated in the parking lot. On Monday, July 25, 2022, smoke and an orange glow were observed emanating from the right rear wheel well of the burned bus. Fire department personnel responded for a third time and applied water to the smoking battery compartment. No additional injuries were reported.
We found that the probable cause of the Hamden, Connecticut, fire on a battery electric transit bus was moisture in the high voltage lithium-ion battery system, which led to battery damage resulting in the fire. Contributing to the injuries to facility personnel was the lack of a safety plan by CTtransit for mitigating risks associated with high voltage lithium-ion battery fires during emergency response.
