By Chris Vagasky
Lightning is one of the most common natural hazards that people encounter in their daily lives. It occurs more than 200 million times around the United States and more than 2 billion times around the world every year. Hotter than the surface of the sun and transferring thousands of Amperes of electricity from the cloud to the ground, lightning is a significant risk to anybody outdoors during a thunderstorm.
With more than 183 million visitors to zoos and aquariums in the United States every year, there is always potential for a lightning-related incident to occur at these facilities. The National Lightning Safety Council recognizes June 20-26, 2021 as National Lightning Safety Awareness Week, so let’s explore this topic in more detail to find out how you can mitigate the risks of lightning at your facility.
Lightning and Lightning Safety Basics
Lightning is a giant electrical spark in the atmosphere that can be as hot as 50,000°F and thousands of times more powerful than the electricity running through the walls of your house. Lightning occurs in every thunderstorm, and is caused by the collision of ice crystals, raindrops, and soft hail in a cloud. These collisions cause a separation of electric charge in the cloud, and when the charge builds up enough, lightning occurs. There is no way to predict when or where lightning will hit the ground, so every thunderstorm needs to be taken seriously to protect guests, staff, and animals.
The basic principle of lightning safety is that there is no safe place outdoors when thunderstorms are in the area. Most lightning victims are struck before the rain starts or after it ends, as lightning can strike even when there is no precipitation in the area. Most people are inside to avoid getting wet by the time the rain arrives, but it is important to remember that the absence of rain does not equate to the absence of risk of a lightning strike. A simple phrase to remember is “when thunder roars, go indoors” – even if the rain hasn’t reached you yet.
Figure 1: Graph showing the threat of lightning casualties. The greatest threat is as a storm approaches or departs, because by the time the storm is overhead, most people are inside to avoid getting rained on.
However, “dry” still does not necessarily mean “safe.” Picnic shelters, pavilions, and other canopies do not provide adequate protection from lightning. When lightning is in the area, the only lightning-safe places are substantial buildings with electricity and plumbing in the walls, like indoor exhibits, restaurants, gift shops, and office spaces, or a fully-enclosed, metal-topped vehicle. Golf carts, open-sided trailers, and open-sided trains do not provide protection.
Who is at risk?
Lightning can occur anywhere around the world at any time of the year, as long as the weather conditions are right. To quantify the risk, you can consider the Zoo Lightning Risk Index (ZLRI) that accounts for the amount of lightning that occurs near a zoo and the number of visitors each year. ZLRI is calculated using the following formula:
ZLRI = (Lightning Density x Number of Visitors)/1000
Figure 2 shows the average annual lightning density for each county in the continental United States. Find the county where your facility is located and use the upper and lower bounds of the lightning density in the above formula to quickly estimate your ZLRI. From there, you can use your ZLRI to estimate your risk of a lightning-related incident using Table 1.
Figure 2: Average annual lightning density by county from 2015-2019, courtesy of Vaisala.
|
Risk Rating |
ZLRI |
|
Very High |
> 100,000 |
|
High |
40,000 – 100,000 |
|
Medium |
10,000 – 40,000 |
|
Low |
1,000 – 10,000 |
| Very Low |
< 1,000 |
Table 1: Qualitative lightning risk based on ZLRI
No matter the average annual lightning density in your area, it is important to have a lightning safety plan in place. Facilities located in more lightning-prone regions of the United States are at a higher risk of a lightning-related incident and therefore should ensure that proper safety and preparedness measures are taken. However, facilities located in areas with less lightning density are still at risk. In fact, the lower likelihood of lightning strikes may mean guests are less aware of the threat that lightning poses, and may be less likely to take safety precautions should thunderstorms approach.
The National Weather Service has two programs that can help zoos and aquariums improve their preparedness for hazardous weather and lightning: StormReady and the Lightning Safety Toolkit. These programs will help you review and enhance your weather plans to be better prepared when hazardous weather strikes. As we are now in the peak of lightning season, take the opportunity to consider where your lightning safe places are and how you will keep people and assets safe in the event of a thunderstorm.
Chris Vagasky is a guest contributor and the owner and chief meteorologist of Tallgrass Weather Solutions, LLC.