Guyed towers, lightning strikes and peopleÆs safety 1

[fa2070]

I’m in the early stages of planning and coordinating the project of a 160 ft. communications guyed tower (steel tubing) for a 9-mile point-to-point 5.7/5.8 GHz wireless link. The final location of the tower is still being discussed, and therefore subject to change if circumstances demand it. Due to space and some other project constraints, we have decided to build the tower as close as feasible to the servers room. My primary concern has to do with people’s safety in the event a lightning strikes the tower while the employees are in their workplaces in the nearby offices (buildings A, B and C) and the warehouses (W1, W2 and W3). Please see the following sketch. Around 200 people work in this campus in an average working day. Of course, we will outsource the design of the tower grounding system to an engineering firm.
Having said that, my questions are:
[ol 1]
[li]Considering the tower legs and guys are properly grounded (hopefully in a unified fashion), do you think the lives of the people working in buildings A, B, C and the warehouses W1, W2 and W3 will be at risk if a lightning strike hits the tower? Is the proposed site to erect the tower (point P in the sketch) too close to buildings A, B, C and the warehouses such that the people working there could be affected by lightnings or their radiation? Or, to put it another way, can the distances in the sketch be considered “safe”? Bear in mind that buildings A, B, C, W1, W2 and W3 exist. It’s the tower that’s not been built yet.
To complicate things even further, the are a dozen and a half trees at the tower site with heights ranging from 50 to 100 ft. As far as I know, trees tend to attract lightnings. In this case, however, there’ll be a lightning rod at the top of the tower. That is, 60 ft or so above the tallest trees. The tower is expected to be 160 ft.[/li]
[li]Then I have a couple of secondary concerns. Assuming the guyed tower is erected at point P and people’s safety is guaranteed during a lightning event, what about the electronic equipment in the servers room (building A), in the offices (buildings B and C) and in the warehouses? Will the lightning-derived electromagnetic fields damage the servers, notebooks, desktop computers, switches and other electronic equipment?[/li]
[li]And in the third place comes fire risk: Could a lightning strike on the tower cause a fire in any of the buildings?[/li]
[/ol]

If point P is not the ideal location to build the tower, what are the minimum safe distances to the nearest office?

Last but not least. It’s our goal to ground not only the tower legs and its guys, but also the power lines and the rest of the equipment that’s going to be installed on the tower. The data cables will be fiber, so there won’t be any risks on that front.

I will highly appreciate if someone can answer these questions. I will also welcome any comments, insights, guidelines, best practices, horror stories or personal experiences you would like to share with regard to guyed towers built in the vicinity of office buildings and their exposure to lightnings.

Thank you in advance.
fa2070

 

[djs]

Human Safety is one of the reasons to hire a Professional Engineer. Raise your concerns with your Engineering Firm. They need to handle this.

 

[OperaHouse]

At the age of 14 I remember sitting in the basement reading durring a storm. All I remember waqs seeing this blue streak coming twards me from the bulkhead door. Next thing I knew it was an hour later and I was 20 feet away from where I was sitting against a concrete wall. Every bone in my body hurt. Lightning had hit a backyard fence 100 feet away. No section of that fence came any closer to the house. Fourty years of hearing stories always end in the same conclusion. Lightning has a mind of its own.

 

[itsmoked]

While not a tower specialist I would expect no issues with your installation. It's a HUGE plus you're using fiber to the tower from the server room. If your guys weren't correctly grounded you could expect a lateral arc from guy #2 into the corner of the server room. Since you will have that guy grounded that isn't going to be an issue.

I would hazard a guess that the entire facility will actually inherit greater lightning safety by having a 160ft lightning rod providing a cone of safety by attracting and conducting any strikes to earth. I'd prefer to be in the server room during a storm.

I would not expect any problems in the server room from this layout. There are probably some specific aspects related to grounding practices that a specialist should guide you on. I'd look for one who understands data centers and how to ground them in lightning zones.

A properly grounded antenna like yours should reduce the chance of fire caused by lightning in any of the surrounding buildings.

It would be appreciated here if you let us know about any specific things you're asked to do by the tower specialists.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TomDOT]

I'm used to radio towers with significant grounding. There are experts in this specialty.

 

[fa2070]

Thanks everybody for the comments. They're much appreciated.
I'm the project manager and also will be involved with the structural aspects of the tower. I'll outsource the design of the grounding system to a specialized firm.

fa2070

 

[paskee]

Rat Bait Stations .... In my field to protect our main crop (say corn or rice) we set up along the periphery rat bait stations, so when they come looking for food they are stopped from infesting the main crop !

Perhaps... if you build 1 to 4 taller, more conductive towers around your main TOWER/structures... it would attract the lightning.

 

[MikeHalloran]

Guyed towers do fall down occasionally. A search suggests the incidence may be underreported.

Whether or not the local AHJ requires a 'fall zone', I personally think it's irresponsible to put a guyed tower near an occupied building unless the building is specifically designed to protect its occupants from a falling tower.




Mike Halloran
Pembroke Pines, FL, USA

 

[fa2070]

Guyed towers do fall down occasionally. A search suggests the incidence may be underreported.

Whether or not the local AHJ requires a 'fall zone', I personally think it's irresponsible to put a guyed tower near an occupied building unless the building is specifically designed to protect its occupants from a falling tower.

Yes, you're right. I was aware of this since the very beginning. The buildings are within falling distance of the tower. I didn't choose the tower erection site nonetheless.

In my view, lightnings are much worse than the tower failing due to wind loading. In the latter case, people might have early hints of the coming storm/strong winds and therefore could take additional safety measures. But yes, boths risks add up. I'll ask the tower designers to increase the safety factor or use four guys instead of three.

Thanks.
fa2070