Hazard Knowledge

Rechargeable batteries are used in a wide range of contexts. Newer-style high energy density batteries, such as the lithium ion (Li-ion) type, are very common and a growing risk. Services should be aware that traditional types, such as nickel metal hydride and older style lead acid, are still in use and that future developments could see the introduction of newer kinds, like lithium iron phosphate (LFP). Uses include:

• Domestic energy storage systems can be charged by renewables, such as solar cells, and then used either by the consumer or for feeding into the National Grid
• Industrial scale energy storage systems are now being used commercially; such systems may consist of many modular units constructed from ISO containers housing thousands of rechargeable batteries
• Portable devices such as:
  • Smartphones
  • Game consoles
  • Torches
  • E-cigarettes
  • Video or digital cameras
  • Laptops and tablets
• Power tools such as:
  • Cordless drills
  • Sanders
• Gardening tools such as:
  • Strimmers
  • Hedge cutters
  • Lawn mowers
• Uninterruptible power supplies (UPS)
• Leisure and mobility scooters
• Hover boards
• A wide range of transport uses (refer to Hazard: Roadways alternative fuel vehicles)

All battery types have a hazard of stored chemical energy. This can cause an increased risk of:

• Release of electrical energy without warning as large electrical currents, which can cause injury, ignition, or localised high temperatures
• Sparking, arcing, or flashing if terminals are short circuited or touch other conductors

Traditional rechargeable batteries can be heavier and have lower energy densities. Most are made from tough non-reactive plastics that contain a water based electrolyte. Only a small number have an open design. Some rechargeable batteries allow user access to inner parts for electrolyte inspection.

Hazards associated with lower energy density rechargeable batteries include:

• Toxic or irritating water based liquid electrolytes, such as copper sulphate
• Corrosive acidic electrolytes, such as sulphuric acid
• Poisonous alkaline electrolytes, such as potassium hydroxide
• Very high discharge or surge currents, for example in a road vehicle battery
• Non-precious metals like lead or copper; elevated temperatures and fires can cause these metals, when in the presence of electrolytes, to react or release vapours
• Release of hydrogen gas or oxygen gas during charging, which can ignite or explode

Newer style, high energy density rechargeable batteries are made from precious metals and organic electrolytes. The metals used often react very readily with water or air and the electrolytes can be highly flammable. These batteries are often carefully sealed so that water cannot enter making it difficult to cool or extinguish fires.

Sensitivity to charging and discharging regimes, mechanical shock, and localised temperature gradients can lead to thermal runaway, rapid unexpected release of flammable gases and liquids under pressure, release of toxic and corrosive materials.

Thermal runaway, an accelerating increase in temperature caused by chemical reactions, can lead to fire, explosion, release of highly combustible organic electrolyte under pressure and unpredictable fire behaviour. This can be the result of temperature variations limited to only one or a small number of damaged cells, and can cause ignition that occurs spontaneously over varying time frames.

Hazards associated with higher energy density rechargeable batteries include:

• Explosive gases produced by reactive metals, such as lithium. Possible chemical reduction of water by a highly reactive metal can produce an alkaline solution and an explosive gas, for example lithium hydroxide (LiOH) and hydrogen (H2)
• Rapid unexpected release of flammable gases and liquids under pressure
• Release of toxic and corrosive materials
• Fire water run-off containing poisonous metals, such as nickel or cadmium, which can release hazardous materials to their surroundings.
• Toxic and explosive gases released can have the appearance of steam

Refer to the 'Health and Safety Executive publication 'Using electric storage batteries safely' for further information.