Lightning risk assessment for hospitals

IEC 62305-2:2024 reports two results. The combined risk R takes in injury to people and physical damage, and the frequency of damage F counts how often a strike could put the internal systems out of action. Its three types of loss are injury to human beings (L1), physical damage (L2) and failure of internal systems (L3). The 2010 edition had four, among them loss of service to the public and economic loss, and the 2024 edition now handles those through F. In a hospital R leads by a wide margin. Many people are inside around the clock, and some of them cannot move and rely on equipment that must not stop.

So injury to people, within the combined risk R, leads a hospital study and carries weight an ordinary building does not place on it. The representative tolerable risk of IEC 62305-2:2024 (Ed.3) clause 7.3 NOTE 1 is the same for a hospital as for any building, although that note allows a different value after a detailed study that weighs how vulnerable the occupants are. The method mainly raises the stakes on the other side: intensive care and operating theatres fall in the highest loss class of Table C.2, and wards of patients who cannot move on their own fall in the next one, so the same strike counts for more and the risk climbs toward the tolerable limit faster. A strike that injures people through touch and step voltages, or starts a fire in an occupied ward, is the outcome the assessment is built to drive down. This is close to the reverse of an unmanned data centre, where the availability of the internal systems leads and life safety is rarely the deciding risk, and it sets the whole tone of the hospital assessment.

For how R and F are put together from their components, read the IEC 62305-2 risk method. For the damage and loss model beneath them, start with what is IEC 62305.

Life safety leads, but it is not the only risk a hospital has to answer for. A hospital is critical public infrastructure for the area it serves: emergency departments, surgery, diagnostics and inpatient care that the surrounding population relies on and that cannot simply pause. A lightning event that takes part of that capability offline, even briefly, affects far more people than the ones inside the building at the time.

That is the loss of service to the public that a hospital study has to weigh. An outage in power, in the clinical network, or in a system a ward depends on interrupts a service the public needs, and the frequency of damage F to those internal systems captures how often a strike would cause it. It rarely overtakes the life-safety risk as the deciding one, but it raises the consequence of an internal-system failure beyond the immediate clinical danger, and it is part of why a hospital is held to a higher standard of continuity than an ordinary occupied building. NFPA 780-2026 and AS 1768:2021 score this as a separate risk of its own, R2, against a typical tolerable value of 10⁻³ per year (NFPA 780-2026 Table L.6.2, AS 1768:2021 Table 2.1).

IEC 62305-2:2024 (Ed.3) clause 5.2 groups what a strike can do into four causes of damage: shock to people from a direct flash (D1D) or from touch and step voltages (D1T), physical damage such as fire or explosion (D2), and the failure of electrical and electronic systems caused by the lightning electromagnetic pulse, or LEMP (D3). In a hospital every one of them carries real weight. Shock and physical damage are the direct threats to life that the assessment always weighs, but D3, the loss of internal systems, is unusually important because so much of the building's safety depends on electronics that fail easily.

Trace where a surge would go. On the power side it can reach the main switchboard, the essential supply boards and the isolated supplies in theatres and critical care. On the signal side it can reach the patient monitoring network, nurse-call, the imaging department and the laboratory systems. Each of those ends in equipment that is either attached to a patient or relied on to decide what happens to one, so a failure in the wrong room at the wrong moment is a clinical event, not only a repair job.

The assessment credits measures along each of those paths. Surge protective devices where every service enters take the bulk of the energy, and further devices on the boards feeding theatres and critical care take what passes. Bonding the building steel, cable trays and metallic services, medical gas pipework included, keeps patients and apparatus at one potential. Screened routes and a lightning protection zone (LPZ) scheme with theatres and intensive care innermost cut the surge before it reaches the bedside. IEC 62305-4 sets out how these measures work against LEMP, and the risk method lowers the probability of internal-system failure for each one in place.

For how surge devices are graded and coordinated, see SPD types under IEC 62305. For the zone scheme, see lightning protection zones (LPZ).

Few buildings are connected to as many conductive services as a hospital. Beyond its power feeds it takes in multiple data and telecom lines, nurse-call and fire alarm wiring, building management cabling, and in many cases metallic medical gas pipework running between a central plant and the wards and theatres. Every conductive service entering the building is a potential surge path, which is why the services, rather than the roof alone, are usually where the assessment finds much of the line-related risk.

On a hospital campus the services are long as well as many. Feeds run between buildings to a central energy centre, a separate imaging block or a remote car park, and each run is exposed for its whole length. A buried, screened cable bonded where it enters lets far less through than an unscreened one on poles. The metallic services need the closest look: a medical gas line or a long signal run that is not bonded and protected where it enters can carry a surge straight into a clinical area, so it is entered as the conductive path it is.

The inputs that decide much of the answer are therefore the list of services, the length, installation and screening of each, the bonding of every metallic one, and the protection at each entry. Getting that list complete matters more in a hospital than almost anywhere else.

Hospitals are built to keep running through a fault. Standby generation, dual power paths and protected distribution to clinical areas exist so that care does not stop when something fails. Lightning is one threat the standby and redundancy do not fully answer, because an induced surge can reach equipment on more than one power path at once and can disrupt the low-voltage signal and data systems the generators do nothing for.

A lightning risk assessment supports the continuity the building is designed for by putting a number on the lightning part of it. It estimates how often a strike-related event could injure someone or take a clinical system offline, and shows that the external protection, surge protection, bonding, shielding and zoning bring those frequencies below an acceptable level. It does not replace the standby power and protected distribution that clinical resilience is built on. What it gives is the recognised evidence that the lightning threat to both safety and continuity has been assessed on the numbers and controlled, rather than left as an assumption that the building is probably fine.

Lumex^™ runs the assessment under the standard your project uses: the IEC 62305-2:2024 method, the NFPA 780-2026 Annex L simplified risk assessment and detailed R1 to R4, or AS 1768:2021 with R1 to R4 each against its own tolerable value. For a hospital you set out the clinical zones, record who is in each and what equipment they rely on, and enter the incoming services in the form the chosen method asks for. Add a surge device or an external system and the risk to life and the internal-system result move with it.

Every figure shows its working and the clause behind it, and the signed report records the assessment for the authority, the accreditation body or the insurer. Lumex^™ does not design the protection system or certify an installation; that stays with your designer. New to the subject? Start with what is IEC 62305, then see the Lumex^™ platform.