Why a tertiary backup power system such as a UPS should be installed in compliance with the HTM in healthcare facilities
The supply of safe, clean electricity is critical to safeguarding lives within healthcare estates. The introduction of more sophisticated clinical and surgical equipment means that any power disturbances would disrupt patient care and could have severe consequences. Equipment failure must be avoided and to assist, the industry has seen the release of more regulations, legislations and codes of practice specific to electrical infrastructure. All of these need to be observed to prevent hospitals and other care facilities from catastrophic outcomes in the event of any power disruption.
The HTM 06-01 Memoranda
A key document that addresses electrical power supply is the government prepared HTM (Healthcare Technical Memoranda), which was prepared to provide comprehensive guidance on best practice design, installation and operation of specialised building and engineering technology used in the delivery of healthcare.
HTM 06-01 focuses on the supply and distribution of electrical services, highlighting the importance of reducing the probability of equipment failure during a primary mains power outage through secondary and tertiary power backup systems.
Although adhering to the HTM 06-01 is not a legal requirement, the memorandum forms the base of a hierarchy, whereby legislation and common law is outlined and therefore an injury or death as a result of failure to implement specific design steps and measures is enforceable by law. A healthcare facility will be held accountable if, in the event its backup power fails, it cannot provide evidence that it has taken every precaution to ensure the power stability of its critical environment. Every effort should be made to meet the recommendations within the HTM so as not to disrupt the delivery of healthcare or put patients at an unnecessary risk.
The recent UK power outage highlighted the importance of applying best practice within hospitals when it was reported that a prominent hospital and a number of other critical care facilities were left without power after a backup diesel generator failed to start. It could be assumed that these sites had not recognised the best practice guidance within the HTM 06-01 as they were left vulnerable to the power failure.
Potential failures of a secondary power supplies are clearly overlooked compared to primary power supply failures. Business ignore the possibility of a concurrent failure to mains power (primary) and the backup generator (secondary) only to be thrown into darkness when a power cut happens. To be HTM compliant a tertiary power solution, such as UPS (Uninterruptible Power Supply) must be installed.
HTM 06-01 Complaint UPS Components
For those with tertiary backup power provisions, it is important that the internal components meet the design set out in the HTM. It is not enough to simply plug in a basic UPS system. Careful consideration must be given to the size, location, configuration and internal structure of the UPS to meet best practice and guarantee patient safety.
Starting with the most obvious component, the batteries which control the reliability of the entire system. To adhere with the HTM guidelines, the batteries should have a 10 year life expectancy to ensure the long-term security of function.
UPS batteries require a suitable environment which will be detailed in the manufacturer’s operating manual, a guideline that is also reflected in the HTM, to fulfil their life expectancy. Typically, the ambient temperature around the UPS should be 20⁰C with adequate ventilation and cooling. At 30⁰C the life expectancy of a typical VRLA battery is reduced to 50% and 25% at 40⁰C.
A VRLA battery is recognised as being a near-zero-gassing battery by the HTM and so presents a lower environmental hazard to the UPS and surrounding area. It is also important to note that the VRLA battery must comply with the BS EN 60896 (21 and 22) standards with threaded insert connection posts and flame retardant case materials.
Another UPS component mentioned in the HTM guidelines is the bypass switch, these should be rotary locking switches located on the input. Furthermore, external battery DC isolators are required in hospital environments. These are ideally situated on the front of the cabinet or an accessible wall.
Although isolation (zero-phase shift) transformers do not feature inside the UPS, they are essential to the overall infrastructure to prevent problems occurring when the input neutral is switched or broken. These transformers can be place on the output, however it is more beneficial for them to be installed on the UPS input. Consideration needs to be given based on the electrical infrastructure design.
The UPS system itself should conform to the following standards:
- BS EN 62040-1
- BS EN 60146-1-1
- BS EN 61439-6
- Energy Networks Association’s G514-1
To meet the minimum requirements of redundancy, an N+1 configuration must be in place. Furthermore, the HTM requires each UPS to be sized with enough capacity to individually be able to fully support the whole load. For example, where the critical load is 100kVA, two UPS systems carrying an absolute maximum of 50% load each would be necessary.
Although the updated, 2017 edition of the HTM 06-01 suggests that modular UPS systems can be used, further consideration is required. Modular redundancy is not treated as true redundancy due to there being multiple points of failure.
All too often dutyholders become complacent because a UPS is already installed. However, without regular maintenance how do you know whether it is still effective and fit for purpose? The HTM covers some of the components within a UPS, but there are many more delicate electrical parts that all need to be working in harmony to provide the power when it’s needed.
