Understanding the Risk From Loss of Supply HTM 06-01

Health Technical Memorandum  06-01- Electrical Services Supply and  Distribution Update 


Changes in application, design and statutory  requirements have led to the introduction of a new generation of equipment and new standards of reliability, hence, the need for an update to Health Technical Memorandum 06-01.

This current review and update of Health Technical Memorandum 06-01 builds on the previous version of the Health Technical Memorandum by enabling users of the revised guidance to provide safer, more resilient electrical systems within their healthcare premises that support the requirements of regulators and ensure a safe environment for patients and staff.

Chart showing grading of loss of supply in a hospital
Grading of Risk in relation to loss of supply 

Understanding the Risk

An electrical system failure can occur at any point or at any time in any electrical system, regardless of the design standards employed. The design and installation of electrical systems inherently allows failure (by operation of a protective device) to minimise the risk of danger and/or risk of injury. This is true of internal PEI systems as well as the wider primary electrical supply (PES) network delivered by the distribution network operator (DNO). 

The effects of accidental damage and the need for maintenance and training should not be 
overlooked. It is essential that an appropriate level of risk management is considered and practical emergency contingency plans are always available and ready to implement. 

The design approach should be mindful of the need to maintain an electrical supply within specific time periods for the safety of patients and staff 

These times can be defined as a supply restored within:

  • greater than 15 s
  • less than 15 s, but greater than 5 s
  • less than 5 s, but greater than 0.5 s
  • less than 0.5 s
  • no-break.

The above times need to be aligned with the distribution strategy and final circuit


The design process should verify that single points of failure leading to loss of electricity supply are minimised by providing the appropriate level of resilience at the point of use. 

All potential points of failure should be considered during the design process. Failures 

of the PEI system are commonly considered as a consequential effect of the failure of the 
incoming DNO supply, main transformer, main switchboard, etc. In all of these scenarios, it is assumed that the SPS (secondary and/or tertiary power supply) becomes available. 

However, failure of the PEI itself is also possible. The SPS design may be different for each type of failure.

Risk to Loss of Supply

This Health Technical Memorandum considers risk of loss of supply in two main elements:

  • Clinical risk (subdivided into patient and non-patient areas); and
  • Non-clinical business continuity risks (subdivided into medical services and engineering services).

Designers and stakeholders should consult with clinical and technical staff by way of the 

Electrical Safety Group (especially clinical engineers, Authorising Engineers and Authorised Persons, where already appointed) to evaluate the overall risk and the measures proposed to address the perceived outcomes. Most critical within this assessment is the mobility and degree of healthcare support provided to the patient, including clinical procedures, critical care and continuity of treatment.

Small healthcare premises such as GP practices and health clinics/centres may have 

areas that fall into the lower grades of risk. Community hospitals may have departments in 
the low- and mid-grading of risk, but are unlikely to be in the higher grades of an acute hospital. Large acute healthcare premises and above may well have departments in all grades. There is no rule that definitively places healthcare premises in any one grade or defines one grade for a particular healthcare site.

The assessment and application of risk can be a simple or complex approach depending 

on size and nature of the services being provided. Each step change in the supply resilience needed will identify a response from the supply infrastructure. This may also be 
associated with a business continuity risk which may alter the risk being assessed. 

diagrammatical representation of the process is shown in the above figure  where a change in colour from green to red represents the movement from very low (where there is no alternative supply in the event of a power failure) to very high (where there should be several layers of support to sustain an uninterrupted supply in the event of a power failure or distribution fault) for clinical risk and similarly for business continuity risk. The graduation of the assessment should be associated with the step changes identified either in clinical risk or business continuity risk terms, together with the distribution structure available.

Assessment process

The business and clinical/patient elements described below are not definitive nor exhaustive but are given to guide the selection process. While the text may suggest five clinical risk grades (A–E) and four business risk grades (I–IV), it is not unreasonable to either simplify these or make them more extensive. In each case it should aid the assessment process, not stifle it. The final assessment may also be influenced by the available supply and distribution solutions.

Consideration of the categories should 
establish a minimum acceptable risk option at 

the point of treatment or care. For the purpose of this guidance, the patient levels described 
are not intended to be exhaustive, but rather an aid to consider the issues. 

Each healthcare facility will have a mixture of grades (clinical risks and non-clinical 

business continuity risks) in varying ratios. The assessed higher clinical or non-clinical and 
business continuity risk for any particular area will determine the adopted electrical 
infrastructure strategy for that area. Designers, stakeholders and the Electrical Safety Group should evaluate the economics of providing different distribution strategies for each area or of applying an appropriate distribution strategy for the highest-order risk to many or all areas.

Within any healthcare environment, there are wide ranges of departments with complex requirements and potential risks. The risk management process should assess each department in terms of susceptibility to risk from total (or partial) loss of the electrical supply.

The consequence of a power failure

The consequence of a power failure is assessed and graded against some broad 
clinical patient groups and patient care plans. This is on a scale from ambulant through to 
critical care. Consequence is also related to the organisation in terms of contingency 
arrangements, emergency preparedness and business continuity, all of which have a financial implication. There is also the operational consequence of the electrical system in terms of the operation and maintenance of the infrastructure from the point of view of both its physical construction and installation, and the managerial and technical staff structure in place to operate the electrical infrastructure.

The level of consequence of a power failure may be evaluated as increasing with the 

level of dependency upon the electrical supply that a patient’s care requires, and will be equally dependent on the duration and extent of the failure.

It is important to assess the dependence certain healthcare departments have on the 

sustainability of the electrical supply. It relates to the reliability of electrical supplies and their subsequent safety requirements. The resilience options can be ranked in time performance (seconds) to re-establishing a supply following an interruption, whether controlled or otherwise.

Within a GP practice or health centre, it may be assessed as acceptable to have single points of failure in a system, given that ambulant patients are likely to be more mobile than patients in critical care areas and staff will be able to move away from the affected area in the event of a power failure. At the other end of the scale, for example in critical care areas or operating theatres, the consequence of a prolonged, or even a very short, power failure could result in serious health disabilities or, in the worst cases, fatality. In this instance, a more resilient infrastructure with additional levels of secondary and/or tertiary power supplies is appropriate.

This article has been extracted from the "Health Technical Memorandum  06-01- Electrical Services Supply and  Distribution " published by the UK government. 

The full detailed document can be downloaded using the below link. 

Download the full Document Here

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