# How to protect an indoor pool from lightning?

What will happen if lightning strikes in an indoor pool while people are in the water? Is there a risk of electric shock for them? Certainly yes, but only if the structure of the building, as well as its lightning protection and grounding, are not properly designed.

When designing the pool structure, it is necessary to pay special attention to the equalization and bonding of potentials. If all parts of the building have the same potential, the risk of being hit by lightning is minimal.

The safest design option is when a building has a metal frame that is continuously connected to the reinforced concrete foundation. In this case, the correct spreading of the current along the structural elements of the building to grounding is ensured - and then into the ground through the foundation ground electrode. It is only left to supplement the lightning protection system with lightning rods. This is the option that the engineers of the ZANDZ Technical Center offered to the customer for lightning protection of the pool. Let's study the project of lightning protection and grounding of this object in more detail.

## Task

To calculate lightning protection of a multifunctional sports complex with a swimming pool. The building under protection is an ordinary structure in terms of lightning protection in accordance with the IS and is in Category 3 according to the AD.

## Solution

Calculations of lightning protection and grounding of a historical object are made in accordance with the following documents:

Protection of buildings from lightning strikes is carried out with the help of lightning rods. A lightning rod is a device rising above a facility that diverts lightning current into the ground without entering the facility. It consists of a lightning rod which directly takes the lightning discharge upon itself, a down conductor and a ground electrode.

## Lightning protection system description

Measures to meet the requirements for the lightning protection system:

1. Installation of 9 rod lightning rods with a height of 4 m on the roof of the building. Lightning rods M1-M5 are welded to the frame, and M6-M9 are mounted on the holder to the wall.
2. Protection zones corresponding to zone B of the AD are shown in Figure 1.
3. The metal frame of the building is used as a down conductor in accordance with clauses 1.6 and 2.12 of the AD.
4. Down conductors M6-M9 made of copper-bonded wire with a diameter of 8 mm are laid from the lightning rods. Then they are fixed to vertical surfaces with clamps GL-11703A and connected to the metal frame with clamps ZZ-005-064.
5. In accordance with clauses 1.8 and 2.13 of the AD, a natural grounding conductor- the foundation of the building, is used as a grounding conductor.

## Calculation of the resistance of the indoor pool grounding device

The type of soil indicated by the customer in geological engineering surveys is marl, loam and sandy loam. The calculated value of soil resistivity is assumed to be 150 Ohm ∙ m.

In accordance with Chapter 3.10 of R.N. Karyakin Reference Manual “Grounding devices of electrical installations”, the resistance to spreading of the current of reinforced concrete foundations of an industrial building is determined by the formula:

where p - soil resistivity, Ohm*m;

S - area bounded by the building perimeter,m2.

Calculated resistance of the grounding device is 1.01 ohms.

Figure 1 - The layout of the elements of lightning protection and grounding device for the historical site

Figure 2 - The facade of the elements of lightning protection and grounding device for the historical site

Components for the external lightning protection system of the pool

Table 1 - Materials requirement list

 № Fig. Product item Product Quantity Lightning protection system 1. ZZ-201-004 ZANDZ Vertical air-terminal -mast 4 m (stainless steel) 9 2. ZZ-203-001 ZANDZ Fastening for a lightning rod to the wall (stainless steel) 4 3. ZZ-202-001 ZANDZ Clamp to the lightning rod for down conductors (stainless steel) 4 4. GL-11149-20 GALMAR Copper-bonded steel wire (D8 mm; coil of 20 meters) 1 5. GL-11703A GALMAR Clamp to the facade / wall for a down conductor with elevation (15 mm high; painted galvanized steel) 20 6. ZZ-005-064 ZANDZ Clamp for connecting conductors (up to 40 mm) 4

Do you have any questions about lightning protection of a pool? Please contact our ZANDZ Technical center!

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