Maintenance of industrial uninterruptible power supply (UPS) systems

Health and Safety Executive - Safety notice

Department name: CEMHD Electrical engineering

Bulletin number: CEMHD1-2022

Issue date: 02/22

Target audience:

  • Operators of industrial UPS systems
    (excluding non-maintainable UPS systems and diesel rotatory UPS systems powered by flywheel and diesel generator)
  • designers, manufacturers, importers and suppliers with responsibilities for providing information for maintenance (and all necessary revisions) of industrial UPS systems
  • contractors providing services that include maintenance of industrial UPS systems


Information prescribed in some original equipment manufacturer's (OEM’s) standard operating and maintenance instructions relating to industrial UPS systems may not be adequate to ensure the continued safe and reliable operation for the intended design life.

Outline of the problem

HSE has recently carried out several investigations into dangerous occurrences that resulted from a failure of industrial UPS systems at onshore major hazard establishments. These industrial UPS systems were supplied by various manufacturers. The failure of these industrial UPS systems typically resulted in a loss of power to industrial control systems, emergency shutdown systems and emergency mitigation systems. Some of these incidents have led to localised fires within industrial UPS systems due to failures of either capacitors or batteries with smoke, excessive heat resulting in failure of the static switch and a failure to provide emergency power via a second UPS. Other incidents due to component failures and outdated firmware have led to unplanned shutdown of a chemical processing plant which subsequently on start-up led to an unplanned release of toxic substances into the environment, and additional demand placed upon other safety related systems. Fortunately, no employees, contractors, or members of the public were injured in any of these incidents.

Operating and maintenance instructions

HSE investigations identified in all cases that the information for maintenance included in the OEM’s operating and maintenance instructions did not provide adequate information to allow the continued safe and reliable operation of the industrial UPS systems prior to the incident. For example, implementation of a suitable maintenance regime. In addition end users had typically not been provided with the necessary revisions of information for maintenance, based on experience in use. For example, some components had much shorter life expectancies than initially predicted. Further, end users are not made aware of any design changes or limitations on use that have a safety implication. For example, firmware upgrades might become essential to ensure continued reliability.

Sales literature typically states that the design life of the industrial UPS systems is between 15 to 20 years and systems are very reliable requiring little maintenance throughout their design life. This implies minimal periodic maintenance is required to ensure continued safe and reliable operation of the industrial UPS systems. HSE observed that the provided operating and maintenance instructions typically do not detail the need to replace all relevant components that are time limited to less than the design life of the industrial UPS system (batteries, filter capacitors, cooling fans, internal RAM batteries, power cards and control cards). Consequently, the maintenance schedules were inadequate, leading to a false sense of safety and reliability by end users.

Action required

Designers, manufacturers, importers and suppliers

Designers, manufacturers, importers and suppliers should review the information for maintenance (including inspection) you provide with your current range of industrial UPS systems to ensure that it satisfies legal requirements.

You should review information for maintenance provided historically to all end users of your industrial UPS systems and determine if you need to provide more up to date information, resulting from experience in use, design modifications, limitations on use or anything else that gives risk to a serious risk to health and safety.

Following this review, designers, manufacturers, importers and suppliers should take steps to ensure, so far as is reasonably practicable, that all affected end users are provided with all revisions of information to assure safe and reliable continued operation.

End users and maintenance contractors

End users and specialist maintenance contractors with responsibilities for ensuring the continued safe and reliable operation of industrial UPS systems should ensure that you have access to the latest revision of information for maintenance from the original equipment manufacturer (OEM). Use this information to update existing maintenance arrangements and to ensure that the installed industrial UPS system is being maintained accordingly.

Major hazard establishments

Where an industrial UPS system is installed to provide emergency power at onshore or offshore major hazard establishments or any other safety related applications, a failure of the industrial UPS system could result in a serious risk to health and safety.

Further guidance on the maintenance and the management of ageing industrial UPS systems can be found in the guidance and further information below.

Is this page useful?