High objects on the ground, especially at elevation, concentrate positive charges that are attracted to the base of a storm cloud’s negative charges, which explains why lightning seems to be drawn to them. The 92-ft. tower will be approximately 60 ft. above the surrounding tree line and it is not uncommon to experience several lightning strikes per day in the summer months. Unfortunately, this is the height of the public’s hiking, BBQ outings, and other activity on the escarpment.
• Colorado ranks third in the country with lightning caused deaths.
• Lightning causes over 10,000 forest, brush, and other types of fires annually.
• Lightning causes millions of dollars worth of damage annually.
• Insurance companies experience heavy lightning-related claims due to the above.
• Lightning could compromise the emergency communications and associated equipment at this location; the very reason this tower is being constructed.
• Lightning takes the path of least resistance therefore, will by-pass high resistance and stay within the thin layer of overburden soil creating potential danger.
• Increased liability,
• Park and recreation green belt is literally within touching distance of the Tower(s) and equipment.
Communication towers are typically not allowed to be constructed in residential areas, for many valid reasons, and if they are it’s usually on private property with no public access. The proposed Log Hill Verizon Tower location presents several unusual risks as the land being considered exists on a small congested lot, of which includes a park and recreation public pathway, as well as the earth being composed of mostly rock, which is resistive and not conductive to lightning dissipation. Good grounds are achieved by good conductive volumetric efficiencies. Therefore, the existing substrate consisting of a large rock mass with a thin layer of conductive overburden soil present less than ideal conditions. The path of least resistance could very possibly be a person, as the human body is made up of approximately 60 percent salt water…a great conductor.
NEC-250 describes grounding concepts including grids, rods, plates, underground water pipes (not plastic pipe), metal frames of buildings, and concrete – encased electrodes. The issue at hand is the grid has to be connected to the source and thereby that area creates exposure. NEC-250.90 to 250.104 has additional details.
NEC – 250.56 suggests a target earth resistively reading of 25 ohms, or less. That implies the lightning discharge would be within the overburden soil, and present risk to hikers and the public at large, within the greenbelt and surrounding areas including Inspiration Point. On a golf course, I have personally witnessed a person struck by lightning over 200 yards away from where the lightning hit. In that case, after striking an aspen tree, lightning took the path of least resistance within the conductive topsoil. It does happen and once is too often. Evidence of the number of potential lightning strikes on Log Hill could be equated with the number of times the Divide Ranch Golf Course sounds the siren as a warning to get off the course. Therefore, one would assume a 92-ft. high Tower would draw substantially more strikes.
The liability aspect of this project should not be taken lightly; it is the harsh reality of business risk mitigation. In the event of an incident, what entity will be responsible, … Verizon, DCWC, the Design/Engineering Firm(s), General Contractor, Subcontractors, Material Suppliers, Vendors, a third party Inspector, or the County (BOCC, Bldg. Inspector, etc.). This should raise questions as to whether or not the county has adequate, or specific, liability insurance for this purpose and if the insurance company has reviewed the final construction documents to integrate their concerns, thereby, possibly lowering the insurance premiums. Also, will the lightning protection system require on-going testing in the future to ensure the health, safety and welfare of the public?
In summary, what makes the Log Hill Tower location a high risk is it’s within a populated residential area, the public access of the green-belt, unfavorable soil conditions, 92-foot tower height at a high elevation, and an existing congested site that’s going to be augmented with an additional building, tower and equipment.
¹Codes: NFPA-99, NFPA-780, Motorola R-56, IEEE-142, IEEE-1100, and FAA STD-019D, NASA-KSC-E0012E, NEC-250, NEC-517, UL, INC.
Reference: NSLI-National Lightning Safety Institute, section 5.5.6, Lightning Protection for Telecommunications Facilities. A-C Lightning Security, Inc., Lightning Inst. Pittsfield, MA, Science Behind Lightning Strikes Nat’l Geographic Documentary 2007.