Guidance to mitigate Li battery system fires

On the evening of Thursday 10 October, there was a small fire in the battery room on board the passenger ferry Ytterøyningen. Firefighting commenced and the ferry reached port under her own engine power. Passengers and crew were evacuated on land. In the morning of Friday 11 October, there was an explosion below deck, in or adjacent to the battery room.

In response, the NMA issued a circular (SM3-2019) on 14 October and clarified it on 18 October 2019, recommending that shipowners using battery systems review their risk assessments and emergency procedures.

Corvus issued guidance, emphasising the extreme importance that vessels do not operate without communication between the EMX (Energy management system) and the battery packs, as this may result in a breach in the transfer of important system data to the EMS/bridge.

LR made the following recommendations:

To support owners or operators reviewing their risk assessment, the following considerations are related to the mitigation of risk in case of fire adjacent to, or within, a lithium battery system space:

* Maintain fire insulation for the space in good condition.

* Do not store combustible material or flammable compounds in the space.

* Conduct regular testing to confirm that the battery management system (BMS) is fully functional and that it remains connected to the ship’s alarm system, so that temperatures can be monitored during an emergency response.

* Investigate alarms and take prompt action before clearing the alarm status, particularly where high cell or ambient temperatures develop.

* Ensure that ventilation for the extraction of gasses remains in a defined safe state during an emergency.

* Ensure that fixed fire-fighting system release instructions are clear, correct and readily available.

* Conduct crew training on the recommended instructions, with fire drills focused on actions necessary and on the timescales.

The LR guidance reiterated that, unlike conventional electrical systems, inherent risks remain even when charged lithium battery systems are disconnected from the electrical power network. The designed safe state for the battery, its electrical connections, auxiliary and ancillary systems in all operating modes needs to be defined, available and include the situations under which the safe state should be activated.

Mitigations based on the ‘fire triangle’ approach of removing ignition source, fuel or oxygen; may have limited effect when dealing with lithium battery system ‘fires’.

If thermal control is lost or if cells are damaged, an uncontrolled chemical reaction or ‘thermal runaway’ is possible, leading to rapid heat gain and the venting of potentially flammable and/or toxic gasses. Battery module designs mitigate the propagation of limited thermal events. In an emergency, reference should be made to information provided by the manufacturer on the removal of heat. Fire-fighting media need to be suited to the removal of heat from the system and the reduction of heat transfer. Water or low expansion foam are best suited to this task.

Keeping the BMS connection active during a fire event allows the propagation of an event to be monitored from outside the space.

Battery module designs may include separate ventilation ducting for gasses evolved and it is often the case that keeping these open during an emergency represents the appropriate defined safe state.