Last reviewed 1 July 2019

Mike Sopp examines the hazards associated with battery installations which provide an uninterruptible power supply (UPS).


Many organisations have safety or business critical systems and/or equipment that require a constant supply of electrical power. Failure or fluctuations in this power supply can have significant impacts including the potential for harm to building occupiers, the loss of data and business interruption.

The provision of a UPS typically in the form of a battery installation is therefore commonplace and is a critical organisational asset.

However, there are hazards associated with battery installations that if not managed appropriately could impact on the availability of the UPS and place occupiers at harm, particularly those who may require access to the battery installation.

Batteries and hazards

A battery installation is used to store electrical energy. For UPS purposes it will be in a fixed location and be permanently connected to both the load and the power supply. In addition to a UPS function, these types of system can be used for alarm systems and emergency power supply.

The type of batteries used will either be chargeable or non-rechargeable, with the former being the most hazardous. Chargeable batteries themselves will normally be lead/acid or alkaline (eg nickel-cadmium) although it should be noted that lithium i-on batteries are beginning to be utilised. In a UPS scenario, lead/acid are the most common type still being used.

The chargeable batteries will either be valve-regulated which are often described as “maintenance free” whereby gases produced do not escape (unless the internal pressure exceeds a pre-determined level) and are converted back into water, or vented that allow the gases produced to escape into the surrounding atmosphere.

The hazards associated with chargeable batteries can be summarised as follows.

  • Electrolytes are solutions containing chemicals that are corrosive (eg potassium hydroxide) capable of causing burns/damage eyes and are also poisonous (eg sulphuric acid).

  • Explosion and fire hazards can be created through the venting of hydrogen at an appropriate concentration and temperature that, if exposed to an ignition source particularly in a confined space can result in a violent explosion.

  • Electrical hazards exist through the stored energy found in batteries, which can be released quickly through both direct and indirect contact with the battery causing electric shock and potential fire hazards due to short circuits.

It should be noted that valve-regulated batteries, when being charged, still have the potential to create a fire or explosion risk if the pressure relief valves open due to overcharging.

Clearly a suitable and sufficient risk assessment will need to be completed in relation to the battery installation, taking account of various legislative requirements such as those contained in the Control of Substances Hazardous to Health Regulations (for chemical exposure) and the Dangerous Substances and Explosive Atmospheres Regulations (in relation to the release of hydrogen).

The latter will also include the need to assess the extent of any hazardous zone that may be present due to the potential venting of hydrogen.

Accommodation and ventilation protection

There will be many influences on the type of accommodation, not least the type and number of batteries required and associated ancillary equipment. BS EN IEC 62485-2:2018 Safety Requirements for Secondary Batteries and Battery Installations. Stationary Batteries states that “batteries shall be housed in protected accommodation” and suggests the factors to consider will be protection from:

  • external hazards (eg water)

  • hazards generated by the battery (eg explosion)

  • access by unauthorised persons

  • extreme environmental influences (eg temperature).

Depending upon the size of the installation, separation can be achieved through the use of dedicated rooms, cabinets or enclosures. In respect of these potential locations, the British Standard noted above makes various recommendations including ensuring the floor can take the load, is impermeable/chemically resistant (where necessary) and “shall be electrostatic dissipative” within arm’s reach of the battery.

Batteries themselves should be mounted on stands or in cabinets, designed to provide good access, particularly to prevent personnel responsible for servicing from having to reach over batteries. BS EN IEC 62485-2 suggests that to allow for emergency egress from rooms, “an unobstructed escape path shall be maintained” with a minimum width of 600mm.

One of the key design requirements relates to ventilation. Hydrogen and oxygen, when vented (either from venting batteries or due to a release valve) into the surrounding atmosphere can create an explosive mixture when the concentration of hydrogen exceeds the lower explosive limit (LEL) of 4% and up to the upper explosive limit (UEL) of 75%.

Health and Safety Executive (HSE) guidance states that “sufficient ventilation should be provided to ensure that the concentration of hydrogen is well below the LEL” with the size of the margin of safety reflecting the risk to people.

There are many factors that will impact on dilution including rate of hydrogen production, location of batteries in an area, size of the area where batteries are located and factors that could impede natural ventilation.

Both the HSE guidance and BS EN IEC 62485-2 provide the necessary formula that can be used to calculate the necessary flow-rates. In summary, because hydrogen is buoyant air inlets should be located at low level and outlets at high level. Clearly location of any battery room/enclosure will determine the need for suitable air ducting to remove gases to atmosphere.

Adequate ventilation will mean that “all but the immediate vicinity of the battery to be identified as non-hazardous when a hazardous area classification is carried out” under DSEAR.

Electrical and electrolyte protection

Similarly, to accommodation design, BS EN IEC 62485-2 states that to protect against electric shock, protection (from direct contact) can be achieved by applying protection by:

  • insulation of live parts

  • barriers or enclosures

  • obstacles

  • placing out of reach.

The standard goes on to state that “doors to battery rooms and cabinets are regarded as obstacles and shall be marked with labels accordingly”. Doors can be locked (from the outside only) while signage should consist of appropriate warning signs (eg hazardous voltage), prohibitions (eg authorised access only) and safety rule requirements (eg eye protection must be worn).

Protection from indirect contact can be achieved through various means such as the use of automatic disconnection of supply, non-conducting locations, insulation and electrical separation. It should also be noted that any stands or cabinets made from metal must also be insulated or connected to the protective conductor.

Access to the location of the batteries should also be controlled with access limited to those with the necessary authority to undertake tasks such as charging, inspection, and maintenance. Competency is another key risk control element and whether personnel are in-house or third-party contractors, competency checks should be undertaken.

The HSE guidance provides useful information on safety working practices that can be adopted for battery charging operations. In terms of maintenance, BS EN ICE 62485-2 states that personnel involved in maintenance operations should be “trained in any special procedures necessary”.

It is also essential that any instructions for use, installation and maintenance provided by the battery supplier are displayed within the vicinity of the battery so that they may be followed during maintenance cycles.

As mentioned above, electrolytes can be corrosive and/or poisonous and as such the main measures to protect persons involved in activities such as maintenance will involve the use of personal protective equipment (eg gloves and goggles) and readily available first-aid facilities in the event of any incident occurring.

Inspection and maintenance regimes should not only include the condition of the batteries and associated terminals and connections but also any safety systems such as ventilation systems and the condition of any stands, cabinets and flooring within the location where UPS batteries are located.


UPS battery installations are a key business continuity asset but present hazards, particularly to those charged with ensuring operational functionality.

Only those who are properly trained and competent should work with a battery UPS installation.

When batteries are being charged, it is essential that the manufacturer’s guidelines and instructions are followed to prevent harm and risks of explosion or fire. Further guidance is also contained in INDG 139 Using Electric Storage Batteries Safely.

Ventilation requirements for charging can be calculated following guidance contained in the British Standard noted below along with HSE guidance INDG 139.

Further information

Available from the British Standards Institution at

  • BS EN IEC 62485 series Safety Requirements for Secondary Batteries and Battery Installations

Available from the Health and Safety Executive at

  • INDG 139Using Electric Storage Batteries Safely