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Home / Resources / DRAFT for industry consultation: Safety of Alternatives to Onsite Diesel: Things to Consider - Onsite Li-ion batteries (BESS)

DRAFT for industry consultation: Safety of Alternatives to Onsite Diesel: Things to Consider - Onsite Li-ion batteries (BESS)

Date Posted: 3 March 2023

The drive to reduce carbon and other airborne emissions from onsite diesel requires alternative sources of energy onsite. In the context of safety, a series of 'Things to Consider' guides are being produced for various alternatives. These are currently drafts, for industry input. This draft covers onsite use of Li-ion batteries.

The following information is currently a draft for industry consultation* – the deadline for comments (to is 1 September 2023.

Li-ion battery storage (BESS)

Li-ion and other battery energy storage systems (BESSs) increasingly provide site energy, along with support for site renewables. Li-ion is a leading type of onsite BESS but other battery types, e.g. flow batteries, have their own practical and safety considerations. BESS should be subject of a pre-site risk assessment (RA) which should consider design and planning, transportation, installation and commissioning, operation and maintenance (O&M), emergency situations and end-of-service life.


Li-ion batteries do not commonly present or fail to danger, but the main operational hazards can be:

  • Electrical failure or contact
  • Mechanical damage (may include impact or vibration)
  • Heat stress – ambient overheating
  • Charging stress – overcharging/incorrect charging practice


Li-ion batteries may hold significant electrical potential. If terminals short-circuit, e.g. with an uninsulated object or due to damage, electrical energy may be released rapidly and unexpectedly.

  • Protection against electric shock must align with BS 7671/IET Electrical Energy Storage Systems CoP for the prevalent site and application, including adequate fault protection.
  • Consider the risk of DC arc flash (Appendix E, IET EESS COP)
  • Have a clearly communicated, safe system of work for battery fault-finding, O&M, replacement, commissioning and decommissioning.
  • Electrical isolation procedures must be clearly communicated to competent staff/contractors, including regard for any battery-reliant critical systems.

To protect from electric shock:

  • Ensure that live conductors are effectively insulated/protected
  • Control personnel proximity to dangerous voltages
  • Prevent any objects from falling onto a battery and its terminals.

In addition to the risk of electric shock, the hazards above can lead thermal runaway, fire/explosion, and chemical leakage. Spitting or explosion may produce hot shrapnel.

Thermal runaway, fire/explosion

  • Thermal runaway may release toxic/flammable ‘off gas’ and lead to vigorous fire/explosion/hot projectiles. Heating can spread quickly, cascading runaway in adjacent battery cells
  • Flammable and toxic ‘white vapour’ is produced (which can be confused with steam)

Early intervention can prevent dangerous thermal runaway. When cell temperature/pressures rise, the detection of ‘off gas’ can provide a vital early warning of runaway. While Li-ion battery failure may also produce detectable smoke, this is normally after thermal runaway has begun.


Li-ion electrolyte mainly comprises flammable organic carbonates (e.g. ethylene and dimethyl carbonate). In normal situations Li-ion batteries are not prone to leakage, but leakage may occur due to:

  • mechanical damage
  • cell breach due to thermal runaway

An emergency clean-up plan should consider health, fire and environmental hazards, in addition to safety hazards. If leakage occurs in an enclosed space, there may be harmful and/or flammable vapours.

Control measures


BESSs are typically bulky, and the internal battery system may be fragile:

  • Do not attempt to manually lift onsite BESS units - use suitable mechanical lifting equipment and ensuring a clear pathway for battery movement
  • Prompt relocation of undamaged (or even damaged) units may be needed, to prevent fire spread.


Separation of BESS from people and (notably flammable) surroundings is a key risk control measure.

The risk of BESS heat stress or thermal runaway can be greatly reduced if batteries are:

  • carrying moderate charge (less than 50%, and lower if possible)
  • not subjected to excessive ambient heat (e.g. strong direct sunlight)
  • in a protected location to prevent crush, puncture, or external heating that can lead to cell thermal runaway/fire. Space battery cells where possible to reduce the risk of heat transfer.
  • separated from any flammable materials.

Indoor BESS storage areas should be sufficiently spacious and ventilated, with suitable routes of emergency personnel egress.

The equipment

  • Poor BESS design/manufacture may lead to unsafe operational failure: BESS should be designed, manufactured and tested in line with relevant product safety Standards and component compatibility. Designs must enable safe routine and emergency isolation.
  • Li-ion batteries typically require electrical management systems to ensure operation within controlled parameters e.g. voltages, temperature and charge states (which adjusts as battery cells age), to prevent thermal runaway/fire.
  • Automatic/sensor detection of ‘off-gases’/prompt battery shut down can prevent thermal runaway and fire/explosion.
  • Establish effective technical contact with your BESS supplier and refer to the manufacturer’s operating manual. Consult the manufacturer regarding safe transport, storage and use, and on emergency measures.
  • Test the BESS promptly when it arrives onsite – cycle (charge/discharge) battery cells as prescribed by the manufacturer.
  • Any fire suppression measures should be compatible with BESS components.

Site planning

  • Ensure the BESS and your procedures meet any site insurance requirements.
  • Consider available battery siting as part of site RA – is there enough: separation from people and surroundings; access for installation and maintenance; protection from accidental site impacts, vibration and flooding? 
  • Would you be able to create a fire exclusion zone if necessary?
  • Is the bedding (the base) for the BESS suitable?
  • Walls and floors must be capable of supporting the weight of any mounted components
  • Establish access to sufficient site cooling/fire-fighting water supply before BESS delivery.
  • Ensure other required fire safety measures and PPE are available onsite.

Contained site batteries

Thermal, flammability and respiratory hazards may be greatly increased in enclosed spaces: specific planning, RA, safety and emergency measures are needed to deal with the risk of leakage and thermal runaway in any enclosed environment (such as a container). Ensure suitable enclosure monitoring and have an emergency runaway/fire procedure in place before starting battery operation.

Emergency planning

Create onsite hazard emergency control plans:

  • a battery damage plan to include how to safely move batteries (which may include damaged batteries)
  • a fire emergency plan to include:
    • equipment isolation/contained battery venting/personnel separation/evacuation – enabling a rapid call to the fire services (note the risk of fire escalation)
    • essential information for the fire services
    • initial cooling/flame fighting measures - avoiding/protecting against combustion products/fume inhalation
  • a clear-up plan to include how any electrolyte leakage will be safely cleared up, including reporting of spillage/firewater.

Competency, training and information

Only suitably trained and competent personnel should:

  • work with a BESS; or
  • engage in BESS emergency measures.

Ensure that anyone involved in testing, connection, isolation and/or charging/discharging, knows safe operational practice and is sufficiently competent (e.g. level 3 electrical/battery trained (e.g. Level 3 Award in Design, Installation and Commissioning of Electrical Energy Storage Systems).

  • Display suitable hazard warning signs, notices and labels for all personnel
  • Communicate BESS operational and emergency safety information with all relevant staff and contractors, e.g. during O&M and RA discussions, toolbox talks.

Operational safety

  • Charge/discharge Li-ion batteries in a suitable, dedicated area
  • Conduct local BESS temperature monitoring wherever possible. Consider thermal imaging/ thermometers/probes, and ‘off gas’ detection - noting smoke detection may be too late to prevent thermal runaway.

Protective equipment (PPE)

For any interaction with a suspect/damaged or leaking battery, properly trained staff and safe working procedures are essential. In addition, provide and use suitable:

  • PPE (to protect the eyes and skin) and insulated gloves
  • If the risk of arc flash is significant - PPE based on IET CoP EESS E3.5
  • Respiratory protection in the event of an electrolyte leak or battery heating/offgassing.
  • If tackling an outdoor fire - fire-resistant PPE, including self-contained BA to protect against heat, gas and smoke.

Emergency measures

Fire can spread to adjacent cells/materials and become uncontrollable. In case of a significant Li-ion battery fire:


Be aware of live battery and any surrounding electrical hazards.

Overheating/early-stage fire

  • Enable equipment isolation/cordoning/evacuation
  • Rapid call to fire services, with essential information to hand (note ongoing risk of fire escalation)
  • Cooling/flame extinguishing with copious water if safe to do so, preventing exposure to combustion products/fume inhalation
  • Trained staff should enable cell cooling where possible (using copious water)
  • Do not open a battery to attempt cooling/firefighting
  • If sufficient water is not initially available use CO2, dry chemical, aqueous vermiculite dispersion (AVD) or other fire-extinguishing agent to help contain fire until copious water is available. Foam is not recommended.
  • A controlled burn with personnel exclusion zone may be an option.

More significant fire

  • Isolate the equipment if possible
  • Rapid call to the fire services, with essential information
  • Cordoning/evacuation, ensuring safety of all personnel and public.
  • If competent fire-fighting personnel are available and it is safe to do so, apply copious water for cooling and to prevent fire spread.

Note: it may take tens of thousands of liters of water, applied directly to the battery, to fully extinguish and cool down a sizable battery fire. This will result in considerable contaminated water run-off.

  • MONITOR BESS TEMPERATURE FOR AT LEAST 24 HOURS - and longer if necessary (e.g. thermal imaging)

Contained site batteries

In the event of an enclosed battery fire, cordon the area and do not enter. Vent if possible, create an exclusion zone and wait for the fire services.

References/sources of further information

(to develop - examples below, should include links).

  • IET Code of Practice for Electrical Energy Storage Systems (EESS)
  • Need to Know Guides RE1 BESS: commercial Li-ion installations v1
  • Need to Know RE2 Li-ion Battery Use and Storage v1
  • National Operational Guidance at:
  • HSE Using electric storage batteries safely INDG139 (rev1)
  • BS EN IEC 62485-2 2018: Safety requirements Part 2: Stationary batteries
  • DSEAR 2002, L138 ACoP
  • IET BS 7671 (Current Wiring Regulations)


To follow at end of consultation.

©2023 CONIAC: *draft - not for reproduction or adaptation without written permission. This content is solely to highlight various safety issues for consideration. None of this content constitutes official/industry guidance or in any way seeks to replace or supersede existing official/industry guidance.