Lightning Pool-Closure Policy

An article that appeared in the November/December 2008 issue of Aquatics International stated that there was no longer a need to clear indoor swimming pools during a thunderstorm. The article noted that there have been no documented deaths from lightning in indoor pools and since the National Electric Code requires bonding and grounding, swimmers would be protected in the water. Unfortunately in order for this to be true, there must be two necessary prerequisites for such a change in protocol:

  • The pool area has to be completely bonded and grounded electrically
  • A complete lightning protection system is required

While current codes require bonding and grounding of the metallic elements in the pool area, most existing pools do not meet that standard because they were built under different regulations. Many new pools also do not comply because though the basic grid is bonded they have added stainless steel lifeguard chairs or metal bleachers that are not connected with the grid.

Additionally, over time concrete and the pool area environment can deteriorate bonding. Therefore, just because a pool was built to code does not necessarily mean that it remains uncompromised. There are ways that an organization can certify that a pool is presently grounded and bonded, but it is an expensive process that must be repeated periodically to ensure that deterioration has not occurred and that new metallic elements have not been introduced. The second prerequisite, a lightning protection system, is not a common component of pool buildings. Therefore, it is often still necessary to clear an indoor pools during lightning storms.

The article also states “’In fact, a pool closure policy is in violation of the National Electric Code section 250.4(A)(1) and you will be subject to regulatory enforcement.’ Dr. Weiss adds that facility operators must understand they are breaking the law by closing indoor pools.” NFPA 70 § 250.4(A)(1) says “Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.” Neither the quoted electrical code nor the more applicable National Electric Code article 680 (Swimming Pools [et al]) mentions either pool closure during electrical storms or regulatory enforcement.

The good news is that national statistics do not include any deaths from lightning to people in indoor pools. This is potentially because organization’s policies are to clear the pools. There are several documented instances of lightning striking indoor pools through glass or open windows and contacting the pool bottom, bleachers or a lifeguard chair. Pools with large expanses of glass have an additional exposure. This is because the glass can be an avenue through which lightning may enter the facility and because a close strike may shatter windows. If the structure has a lightning protection system, that potential may be increased because lightning protection systems do not repel lightning—they attract it to a specific point so the energy can be directed to ground without damaging the facility. A close strike creates a significant sonic disturbance that could cause glass to fall on those in the pool area.

The Redwoods Group, American Red Cross and National Lightning Safety Institute continue to recommend the proactive action of removing swimmers from indoor pools as a lightning storm approaches and until after it passes. This protocol includes keeping swimmers out of the showers, away from telephones and clear of metallic objects or large expanses of glass until after the storm passes. Leaving the premises is also not advised.

People come to indoor pools to have fun; however we must also remain diligent in clearing the indoor pools during thunderstorms. Make sure your organization has a policy in place, that staff know what the triggers are for the pool to be closed and communicate often to members about what your policy is.