SHOCK THERAPY

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

The Victorian lightning-rod umbrella, and the modern Lightning Hopkins (left).

Protecting Trees

Any tree whose trunk is within 10' of the house and whose branches extend above the roofline should have its own lightning-protection system to prevent side-flash to the house. You may also want to protect trees that could fall on the house or that have particular value.

Use the same material specifications for trees as you would for the house. Place air terminals as high as possible in each main branch, and interconnect the down conductors at branch intersections. If the trunk diameter is greater than 3', use two down conductors. Leave slack in the down conductors to allow for growth. Typical grounding solutions are to use three 10' radial conductors in trenches or a single radial conductor extending at least 25' or to the branch line, whichever is greater.

Personal Protection

Up to this point, lightning protection has been mainly a matter of economics. Houses, computers and trees can all be replaced, given enough time and money, so it might seem logical to forgo a $1,500 investment in lightning protection in cases where the risk is relatively low. But when it comes to loved ones, cost-benefit analysis just doesn't apply. Fortunately, protecting oneself from being struck by lightning is mostly a matter of understanding the nature of the hazard and practicing good sense.

If at all possible, stay inside a substantial building during a thunderstorm. Put as many walls as possible between you and the outdoors, stay away from windows and doors, and don't use the telephone.

If you're stuck outdoors, though, there are still good and bad places to be. The one bit of advice most people know is to stay out from under lone trees, but there's plenty more to it. For instance, a spot within a grove of trees all about the same height and growing in a depression may be very safe. Rather than rely on maxims, it's better to try to understand mechanisms. Think of lightning as a great big spark looking for an easy path to the ground. Your goal is to avoid becoming part of that path and to keep your distance from things that might. Let's study some examples.

Avoid any location where you project above the landscape. The principles are the same as for siting a house: Valleys are best; mountaintops are worst. Similarly, being in a boat without a mast is a very risky proposition in a thunderstorm. By the same token, a person sitting on a tractor in an open field can become a very effective lightning rod. On the other hand, an automobile with a solid metal roof is actually a fairly safe place to be, since the charge of a direct strike will most likely be carried through the car's skin and will arc to the ground. But avoid seeking shelter inside a shed with a metal roof supported by wooden poles. In this case, your body might look like the least resistive path from the roof to the ground. Metal objects, in general-including fences, pipes and clotheslines—are likely to be struck, so steer clear.

RSS | Comments | E-mail | Print