Lightning & Thunder

As kids, most of us heard about lightning and thunder from a sage elder trying to aid an intimidated child with a scientific explanation. When you see lightning, count the seconds between the lightning and the thunder to determine how many miles away the lightning struck.

"One-thousand-one, one-thousand-two," we found ourselves counting. Soon the inevitable question surfaced: What if the lightning and thunder come at the same time? It means there is a strike not one mile away, but very close.

Although wireless carriers would love the luxury of counting one-thousand-one, one-thousand-two between lightning and thunder to know the strike is at least two miles away, it is not that easy, and it seldom happens like that. That is why carriers include some sort of lightning protection or prevention into their cell-site plans. And with good reason.

According to the National Lightning Safety Institute (NLSI), there are more than 2,000 thunderstorms happening at any one time around the globe. These storms produce roughly 100 lightning strikes to the earth every second. The institute also reported that lightning causes more damage in the United States than floods, hurricanes or tornadoes.

Also, according to NLSI, major U.S. lightning codes and standards are "incomplete or superficial, providing more benefit to commercial vendors than to those seeking relief from a strike event." For companies promoting devices that "prevent lightning strikes," that "predict the first strike" or that "establish a dome of protection," the NLSI suggests these claims "only serve to confuse the responsible architect, engineer and facilities manager."

Depending on whom you talk to, the area of lightning protection is one of vagaries and shades of gray. According to vendors, carriers do not have the proper amount of protection. Probably the most adamant in this regard is Jerry Kerr, Lightning Eliminators & Consultants marketing manager.

"Carriers usually put in woefully inadequate coverage," Kerr said. "They typically don't provide the proper specifications for the system."

Kerr said most carriers don't consider the losses in their maintenance budgets. Because of that, his company often solves problems after the lightning damage has been done. Kerr blamed engineering firms that specify what they always have used in terms of lightning protection. According to Kerr, the technology has evolved so completely that those specifications could be akin to protecting $300,000 equipment with an 8-plug surge suppression strip.

The tragedy to this, according to Kerr, is that carriers think they have protection. "Unfortunately, they find out how inadequate it is when they receive a bill for $300,000," he said.

Points of Vulnerability According to Kerr, roughly 80% of the wireless cell sites in the United States have insufficient lightning protection from the electromagnetic pulses that come from the ground or the atmosphere.

Kerr explained that not all lightning strikes result in total blowouts. He said sites can experience moderate damage, which can occur repeatedly over extended periods of time. Of course, the result is similar: The system blows out when you need it most. Because the electromagnetic pulses can generate anything from a slight to a severe strike, a carrier can suffer damage to low-voltage equipment or PC cards that may be immediately undetectable. Over time, however, it degrades performance.

Not all vendors and carriers agreed with Kerr's 80% assessment. Mark Harger of Harger Lightning Protection, for one, said carriers are much better about providing a total systems approach to lightning protection, including RF protection, telco protection and grounding. He said this approach at best reduces the relative risk.

Louis Kao, Sprint PCS Western Region implementation manager, suggested that the 80% seemed a little high as well.

"Keep in mind that PCS is the second generation of the wireless business," Kao said. "We learned all of the mistakes from cellular already. We already paid the first time around."

Field Recommendations Kao, who has responsibility for all Sprint PCS sites west of the Mississippi, said he follows three basic tenets in preparing sites for lightning.

"The most important thing to be aware of is that designing a grounding system is just like buying insurance for your investment," he said. "One lightning strike hits you, and all of your equipment will be gone. So, don't be stingy."

Tim Crawford, Andrew product marketing specialist, agreed with Kao. He said the amount of money you invest in lightning protection as insurance can be made up easily if you compare it to the loss of revenue you wouldexperience with downtime.

Second, carriers should hire an expert to evaluate soil characteristics. Kevin Leary, managing director for The Avoca Group, an engineering planning and consulting firm, agreed that testing the soil at the site is critical. The company typically tests the soil resistivity to determine how good or bad it is for grounding purposes. Sand, rocks and a ground water table that fluctuates from season to season can change your grounding requirements.

Finally, Kao said the grounding system must be designed according to what you find out about the soil characteristics. Grounding rods run from eight to 10 feet. However, if the soil has an unusually high saturation of sand, Kao said, it may require a much longer grounding rod to have any effect.

Last Stroke Given the advances in lightning protection equipment, is it possible for a wireless carrier to achieve 100% protection at a site? According to Avoca Group's Leary, probably not. He recommended that wireless carriers take a broad systems approach to protecting their sites. That is, protect the three points of lightning entry -- down the signal cable of the tower structure, through the power lines and through the telco lines. Then, he said, back that up with a good grounding system.

"You'll never get 100% protection. After all, lightning is an act of God," Leary said. "If lightning is going to strike, it is going to strike. The best you can do is allow it to happen and dissipate it the best you can."

One-thousand-one, one-thousand-two, one thousand-three...

Lightning Preparedness On its web site, the National Lightning Safety Institute (NLSI) concludes that lightning is capricious, random and unpredictable. The best solution is a lightning preparedness plan to "mitigate" the consequences of lightning.

NLSI provides an 8-step guideline for preparing your site for lightning. The premise of the guideline is that lightning will strike your site. The steps provided here will help reduce your site's risk.

1. Strike probability study

* Historic 5-year lightning data from the archives

* Future strike estimates via simulation

2. Site inspection

* Identify safe/not safe personnel zones

* Identify potential coupling (dc, capacitive and inductive) to critical and non-critical areas

3. Lightning detection & personnel notification

* Define criteria for cessation of activities

* Acquire appropriate lightning detection and signaling devices

* Integrate decisions into overall safety program

4. Comprehensive employee safety information

* Provide all affected personnel with defensive preparedness information

5. Grounding analysis

* Complete electrogeological model

* Review merits of various grounding options

* Ensure grounds meet target resistance

6. Air terminal/downconductor/bonding/shielding evaluation

* Evaluate existing system

* Consider design options

* Select and install appropriate devices

7. Transient voltage suppression

* Study all conductive penetrations

* Identify vulnerabilities and define protective zones

* Install power and signal protection devices

8. Implement recommendations

* Verify correct installation of all devices

* Certify site as having adopted "best available technology" for lightning safety

* Establish site inspection and maintenance programs.

Assessing your risk in relation to lightning requires that you consider six key areas, according to Harger Lightning Protection.

To determine the need for protection against lightning for a given building or structure, consider the following variables:

1. Type of structure

2. Type of construction

3. Relative exposure

4. Topography

5. Occupancy & contents

6. Lightning frequency.

For more information about this risk assessment, visit Harger's web site at www.harger.com.