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HomeMy WebLinkAbout04201994I City of Sebastian 1225 MAiN STREET n SEBASTIAN, FLORIDA 32958 TELEPHONE (407) 589-5330 n FAX (407) 589-5570 I AGENDA I SEBASTIAN CITY COUNCIL SPECIAL MEETING WEDNESDAY, APRIL 20, 1994 - 7:00 P.M. CITY COUNCIL CHAMBERS 1225 MAIN STREET, SEBASTIAN, FLORIDA ALL PROPOSED ORDINANCES AND INFORMATION ON ITEMS BELOW MAY BE INSPECTED IN THE OFFICE OF THE CITY CLERK, CITY HALL, 1225 MAIN STREET, SEBASTIAN, FLORIDA. PURPOSE: 1) VICKERS GROVE SUBDIVISION - MAJOR MODIFICATION TO PRELIMINARY PLAT - CONTINUATION OF 3/26/94 HEARING 2) BID AWARD - LIGHTNING PROTECTION - P.D. 3) JULIAN PROPERTY PURCHASE AGREEMENT 2. 3. 4. 94. 073 PG i 94.112 PGS 3-12 CALL TO ORDER PLEDGE OF ALLEGIANCE ROLL CALL SPECIAL MEETING ITEM Vickers Grove Subdivision - Major Modification to Preliminary Plat - Continuation of 3/16/94 Hearing (Utilities Director Transmittal dated 4/14/94) Bid Award - Lightning Protection for Police Department (City Engineer Transmittal dated 4/14/94, Bid Tabulation, City Engineer Memo dated 4/14/94, Excerpt NFPA78) 94.108 C. Julian Property Purchase Agreement (No Backup) 5. ADJOURN ANY PERSON WHO DECIDES TO APPEAL ANY DECISION MADE BY THE CITY COUNCIL WITH RESPECT TO ANY MATTER CONSIDERED AT THIS MEETING (OR HEARING) WILL NEED A RECORD OF THE PROCEEDINGS AND MAY NEED TO ENSURE THAT A VERBATIM RECORD OF THE PROCEEDINGS IS MADE, WHICH RECORD INCLUDES THE TESTIMONY AND EVIDENCE UPON WHICH THE APPEAL IS TO BE HEARD. (286.0105 F.S.) IN COMPLIANCE WITH THE AMERICANS WITH DISABILITIES ACT (ADA), ANYONE WHO NEEDS A SPECIAL ACCOMMODATION FOR THIS MEETING SHOULD CONTACT THE CITY'S ADA COORDINATOR AT 589-5330 AT LEAST 48 HOURS IN ADVANCE OF THiS MEETING. 2 I I I I I I i I I I I I I I I I I I City of Sebastian 1225 MAIN STREET g SEBASTIAN, FLORIDA 32958 TELEPHONE (407) 589-5330 n FAX (407) 589-5570 SUBJECT: Vicker's Grove S/D Preliminary Plat Approval City Manager, Dept. of Origin Utilities Utilities Director Date Submitted: April 14, 1994 For Agenda Of: April 20, 1994 Exhibits: None EXPENDITURE REQUIRED: N/A AMOUNT BUDGETBD, N/A APPROPRIATION RBQUIRED, N/A SUMMARY STATEMENT Randy Mosby of Mosby and Associates, Inc., engineer for the Vicker's Grove Subdivision, has requested an extension of time for submittal of the preliminary plat for Council approval, pending the completion of the redesign of the water and sewer systems. Me has not requested a time certain at present, but estimates that the revised plans for the water and sewer systems should be completed in approximately two to three weeks. The Utilities Department would request two to three days for review and comment after the plans are submitted. RECOMMENDED ACTION Since a hearing must be held on this quasi-judicial matter, it is recommended that Council call a special meeting for May 18. 1994 to continue this item. City of Sebastian I 1225 MAIN STREET [] SEBASTIAN, FLORIDA 32958 TELEPHONE (407) 589-5330 [] FAX (407) 589-5570 SUBJECT: Lightning Protection ) System for Police Department) ) ) ) ) Approved for Submittal By: ) ) ) City Manager .~_d/V~ ) / ) Agenda No. Dept. Origin Date Submitted {74/.//2. ENG/P~ 04-14-94 For Agenda of 04-20-94 Exhibits: Bid Tabulation Eckis Memo 4-14-94 Excerpt NFPA78 EXPENDITURE AMOUNT REQUIRED: BUDGETED: $ 7,160.00 $0 APPROPRIATION REQUIRED: S 7,160.00 SUMMARY STATEMENT Four bids for the lightning protection system for the Police Department were received on March 21, 1994 and read aloud at 2:00pm in the City Managers conference room. See attached bid tabulation list. Ail four bids were reviewed and it was determined that ARK, Bonded and Premiere lightning protection companies met the bidding specifications. However, McLean does not have a state certification or does not hold a competency card to install the lightning protection system pursuant to City's licensing requirements. I requested all licenses held by the contractors to be submitted to the city for review with a list of projects that each company has completed within the last two years. It was apparent from the list that McLean Lightning Protection had installed lightning protection for mostly residential homes. However, he had subcontracted once to install lightning protection for the blimp hanger at the Daytona Airport. He identified that he is using the electrical license of Harvest Electric, ER#0012355. He has submitted an exemption of workmans comp insurance because he is a one man operation and does not have any employees. Page 2 Lightning Protection Police Department April 7, 1994 The second low bidder was Premiere Lightning Protection located in Altmonte Springs, Florida. The company is registered with the Department of Professional Regulations through the electrical contractors licensing board as an electrical contractor and is currently licensed in the City of Sebastian. The lightning protection system at the Police Station was not a budgeted item for fiscal year 93/94. However, funds are available through the capital pro3ects fund which has allocated $50,000.00 to the Police Station for either repairs or replacement of the cooling system. From the reports received to date, it is apparent that the cost will fall way below the $50,000.00 allocated. Therefore, funds would be available to install the lightning protection system with adequate reserves to make the necessary repairs and/or replacement to the Police Departments cooling system. The approved bids were determined to be fair and competitive and that the contractors are qualified to install the lightning protection systems. RECOMMENDED ACTION Move to award the lightning protection installation for the Police Department to Premiere Lightning Protection Company of Altmonte Springs, Florida for $ 7,160.00. I I I I I I i I i I I I I I I I I i City of Sebastian 1225 MAIN STREET ~ SEBASTIAN, FLORIDA 32958 TELEPHONE (407) 589-5330 n FAX (407) 589-5570 BID TABULATION CITY OF SEBASTIAN BIDS DUE MARCH 21 1994 2:00 P.M. CONTRACTOR/VENDOR ARK Electric of Veto Beach Bonded Lightning Protection Systems Premiere Lightning Protection McLean Lightning Protection AMOUNT S 9,728.00 $ 7,995.00 S 7,160.00 $ 6,700.00 DATE: TO: 'FROM: RE: City of Sebastian 1225 MAIN STREET n SEBASTIAN, FLORIDA 32958 TELEPHONE (407) 589-5330 ~ FAX (407) 589-5570 MEMORANDUM April 14, 1994 Joel Koford Manager City Engineer, Public-Works Director Lightning Protection System Sebastian Municipal Police Station As you requested, I am filing this report to respond to several comments and concerns which had occurred at the regular city council meeting of April 13, 1994. it is my understanding there was concern that the police antenna tower had not been properly grounded and reference was made to a memo from Ed Gilcher dated September 27, 1993. I contacted our consultant, R. J. Vadimsky, who designed the lightning protection system for the police station and he assure me that the plans would indicate proper grounding for the antenna tower. I have reviewed the plans and note "G" states the following: "NFPA 78 Lightning Protection Code is the minimum standard for this installation. Ail components, equipment and the installation itself shall meet the intent of this code." The lightning protection code does identify a class of materials that are acceptable for the lightning protection installation and the consultant will make a final inspection of the entire system to assure that the materials and installation meet the requirements of the code. The construction drawing is available in the City Engineer's office for review. I I' I i I I I I i I I I I I I I I I I Page 2 Lightning Protection System April 14, 1994 Mr. Vadimsky has twenty years of experience as a mechanical/electrical type engineer. My association with him has always been professional and I personally know that he is qualified to design the lightning protection for the police department. We had worked on several pro3ects together, including the Trident Missile Assembly Facility located at Kennedy Space Center. The lightning protection system for this facility consisting of eight buildings and it was his responsibility to design the lightning protection system. The drawings that he has prepared for the Police Department lists NFPA 78 Lightning Protection Code as the minimum standard for this installation and materials. I have review portions of that code and have circled paragraphs that are relevant and show compliance · with the code for the protection of the tower. The paragraphs are as follows: 3-22 Common Grounding - All grounding medians shall be bonded together. This shall include lightning protection, electric, telephone, antenna system, grounds and underground metallic piping systems which enter the structure. This paragraph specifically identifies a requirement, that separate systems be bonded together, which allows them to act as one. 3-26 Antennas - Radio and television masts of metal located on a protected building shall be bonded to the lightning protection system with a main size connector and fittings. The antenna tower that is located on top of City Hall is connected to the loop on the top of the roof. This loop is connected to a ground loop under the ground by down runs at various points along the outside of the building. 4.2 Mast, Spires, Flags, Polls - These slender structures require one air terminal down conductor and a ground terminal. Electrically continuous metal structures do not require air terminals or down conductors, but do require ground terminals. In this case the tower is considered a metal structure and does not require an air terminal. 4.4 Metal Towers & Tanks - Metal towers and tanks constructed so as to receive a stroke of lightning without damage need only bonding to ground terminals as required in Chapter 3, except as provided in Chapter 6. Page 3 Lightning Protection System April 14, 1994 Here again reference is made that metal towers need only be bonded to ground terminals and that an air terminal is not required. 6-3.3.5 Masts of Wood - Used either separately or with ground wires shall have an air terminal securely mounted to the top of the poll and connected to the grounding system. This paragraph identifies that some structures that are not electronically continuous be required to have an air terminal, a main connection to a ground terminal. As shown and indicated on the plans, the tower is bonded to the grounding system and is connected to a ground terminal. It is apparent that it meets the requirements of the NFPA 78 Lightning Protection Code as identified from the above reference paragraphs. I am not a lightning protection expert but based on my review of the NFPA 78 Lightning Protection Code and the conversation that I had with the consultant, I can safely say that the antenna tower is protected from lightning and meets the requirements of this code. If it is the desire of the City Council, staff can investigate this matter further to be positive that we are doing everything that is to be considered state of the art lightning protection for the antenna tower by having a short report prepared by our consultant. I feel that the bids received by the contractors are fair and competitive and that the lightning protection system is in accordance with the NFPA 78 Lightning Protection Code. The bid should be awarded to commence the installation of the system on the police building to insure that it is protected. Staff can continue to investigate this matter further and if it is determined later that additional protection can be obtained for a reasonable cost, then the City could decide to enter into a change order with the contractor, install it ourselves, or seek the services of a another installer. I would suggest to move forward with this project without causing delay for the protection to the Police Department. lig-pd I i i I I I I I I i I I I i I I I I I I I i I I I i I I I I I I I I I I.ICIVI'NING PROTF. t:TION (0.6 m) from the foundation or exterior footing and ter- minate by attachment to a buried copper ground plate at least .032 in. (0.8 mm) thick and having a minimum sue: face area of 2 sq ft (0.15 m~). 3-21.4 Soil Less than One Foot (0.3 m) Deep. If soll is less ti, an Ift (0.S m) in depth, down conductors shall be connected to an encircling (coonterpoise) conductor in- stalled in a trench or in rock crevices around the struc. ture. The counterpoise conductor shall be not less than the equivalent of a main size lightning conductor. Op- tional ground plates may be attached to the counterpoise conductor to enhance its earth contact, where the measured grounding resistance is found to be too high to provide effective grounding. Grounding in soil less than 1' (0.3m) deep lrig'ure 3-21.4 protected structure, gas piping, undergTound conduits, underground liquefied petroleum-gas piping systems, etc. Main size conductors shall be used for bonding other grounding systems to the lightning p/'otection system. 3-22.1 Common Ground Bofidlngs. If electric, telephone or other systems are grounded to a metallic water pipe, only one bonding connection to the water pipe system is required provided the water pipe is elec- trically continuous between all systems. If it is not elec- trically continuous due to the use of plastic pipe sections or for other reasons, the non-conductive sections shall be bridged with main size conductors, or the bonding Con- nections shall be made at a point where electrical con. tinuity is assured. $-23 Bonding of Metal Bodie~. Certain metal bodies located ttside or inside a building contribute to light. nj,- -is because they are grounded or assist in pro- th to ground for lightning currents. Such shall be bonded to the lightning protection ' metal bodies are further .defini;d as primary or secondary metal bodies in 5-23, I and 3.2:5.2. 3-25.1 Primary Metal Bodies. Primary metal bodies are those grounded metal objects located at or above roof lev(-! that are not within a zone of protection. These primar.y metal bodies shall be bonded to the lightning protection system. Required bondings shall be made using main size conductors, if the primary metal body is subject to direct strikes and the metal thickness is less than g, in. (4.8 mm). air terminals are required in accor- dance with Section ~-9. ~-23.2 Secondary Metal Bodies. Secondary metal bodies are those located anywhere within a zone of pro- tection or below roof level. 8-28.8 Bonding Requirements for Secondary Metal Bodies. in determining the necessity of bonding a sec- ondary metal body to the lightning protection system, the following factors shall be considered: (a) Bonding is only required if a side-flash to the light- ning protection system or to another independently grounded body is possible. (b) The iflfluence of a non-grounded metallic body, such as a metal window hame in a nonconductive medium~ is limited to its effectiveness as a short circuit conductor, should a side.flash occur, and therefore does not nece?sarily require bonding to the. lightning protec- tion system. (c) Bonding distance ~equiremems depend on a tech- nical evaluation of the number of down conductors, the interconnection of grbUnding systems, and conductor resistance and inductive factors. 3-24 Determination of Bonding Distances. Sections $.24.1 and 3-24.2 present a basic and a technical method by which bonding disiances rhay be determined. In general, much less bonding will be required if one uses the technical method making a careful evaluation of the grounding system and reducing the inductive effect in the down conductors. The bonding distance (D,) is the sum of the resistive (D,) and inductive components (D~). (Dr= D. + Dr) 8-24.1 Determining the Resistive Component for an Independently Grounded Metallic Body. if the grounded metallic body in question is directly bonded to the lightning protection system within 12 ft (3.6 m) of the lowest point of the closest down lead conductor (measured length of the down lead, not the bonding con- ductor), the resistive component shall be considered to be effectively zero. If the grounded metallic body is not bonded to the lightning protection system as above, the resistive component of the bonding distance shall be calculated from a forrhula involving the ground resistance of the lightning protection system (R ohms). This ground resistance shall be measured with a tech- nique similar to that described in Appendix J, and shall be measured independently of the effect of any other ground such as a utility company'k ground. (a) Basic Method. Interconnect all separately bgrounded systems within 12 ft (3.6 m) of the base of the uilding and assume the resistive component (D,) to be I ~.i second grounded object, is less than the bonding distance with care. tloles to receive the shank of the fastener sO.r?n -. ~; be made between the lightning protection system and the I preferab y .... . ..... h il ~i grounded object but need not run through, or connect to I motor joints, when me .anc.nors are ms,ta~.mo, t.ne llt. s a _ :~'~ the isolated conductive body (see Figure 9-24.9). Ibe tight so as tn exclude tad accu.m, ulat,.on, ut mo,sture1 landreduce the possible resultant effect o, ,rust. I i'; Illghtnt.g conductor I $-2g Connections. Connector fittings shall be used on ~i: I I all lightning conductors at "end.to-end" 'tee" or "Y"m : I II . I splices. They shall be attached so as to withstand a pull' I a b II I testof 200 lb (890 N). Fittings for connection to metall ?'~ I ..... ~ ..... II I tracks, gutters, downspouts, ventilators, chimney exten- i ^ I U t~ I stuns, or other metal parts about the structure shall bern T ~ I made tight to the object by compression under bolt' !3 [ Il / heads. Crimp type, high compression bolted or weldedl ~_~ [ 11 gro~mded object / connectors are acceptable. Crimp type connectors are not ~': / Il(water pipe. etc.) ] acceptable as Class II materials. · ~: .J_L_ -~_ I may be required, disconnectors shall be installed on all ~i? - ' but' one ground terminal of the system. · f'i If,. ~,c.~,cul.ated. b.o,di,..g .~.i,t~.,.ce. S-~! Concealed S,stems Reouirements covering ex-I ~:. then O0~d A tO ~ ulreclly. ~. posed systems also apply to concealed systems except con- ~.~ If a + b > calculated bonding distance, ductors may be coursed under roofing materials, under,a, ~. bonds not required, roof framing behind exterior wall facing, between wall, ~'f: i studding, in ~onduit chases, or embedded directly in co.nll Fi ,, -.,,.?, crete,or mpo.ry a co,.ducto,, ~i Bodie~, Such as Window Frame. in Non-~,onaueti-e Morea. meta~ conuuit, it snail De oonaec~ to me conduit at mem~ ~ i~oints where it enters and where it emertes from the con-' ~:' 3-25 Water Pipe Bond. If a metal water pipe sYStem is ~lu~t, ~ 1 ~-~. 5-24 shall be connected either to the metal a pipe or may be attached to the outside of a chimney and car-· s stem the nearest h htnln conductor or to another ~'~ y . 'g ' g , tied through the roof to the main concealed conductor. ~: metal body already connected to the sysltermu~tuWrah~no~he:r , ['i. metal bodies are bonded through their s ' 3-31.2 Concealment sn Concrete. In a concealed in-i uon to the metal water t s stem no addmonal bonding I~i ' p'pe Y '' ' stallation where conductors are embedded in concrete,~ ~ is recluire the reinforcing Steel shall be bonded to the cable with a t~~ ~ .' '~ main size conductor. Reinforcing steel shall be b?nded atm ~[:, ~ ~~ ~o_ _t~ .rn_et.[,: N the top and bottom of each embedded down lead. ~f room :I~! jr ~"_~_~_J~_'J:~. I conductors are similarly embedded, connections to rein-~ ]~i~ [ I~ a mum a,ze conuu~,~,~,~ forcing ,reel shall be made at intervals not exceeding 100 .~..!: · ft (SO mt. ' I ~i' - g ' g 3-$1 $ Grounding. Ground terminals may be Iocatec~ $ 27 Ls htmn Attesters, Protectors, and Antenna .~.! Dischar~,e Units. Lightning arrestors, protector~, or at tl~e nerimeter ~f buildings and structures below the ~"ii antenna discharge units shallbe installed on electric and basement floor level or may be carried out at grade level.. ~i!'' telephone service entrances and on radio and television and made as required for'exposed systems. Ifa ground~ ~' i. antenna lead-ins, terminal is located below the basement floor level, it shall~ :~i'.' ............. be in contact with earth for a distance of not less than 10 ~ ~-zls fasteners. ~onauctors snau de securely tastene~ t m a d de ex a.. . f (5 ) n not less than l0 ft ($ m) belowgra copm !" to the buiidin or other ob'oct upon which mey are [i g' J ...... r ........... ~ ~' ........ ' ..... -- placed, at intervals not exceeding 5 It (.09 mt. lne ~,,.' necessary, shall not be subject to bred g nd $-32 Structural Steel Framing. The structural steel · .~i. the same material as the conductor or of a material framework of a buildin£ may be utilized as the main con~ ~' "~' · uall as resistant to corrosion as that of the conductor ductor of a lightning pr~otection system if it is electricall~ , 2 '; q Y ' an ' ' No combination of materials shall be used that forms continuous or ~s made so. ~ electrolytic couple of such nature that, in the presence of , ~: moisture, corrosion will be accelerated. 3-32.1 A~r Terminals. Air terminals shall be bondec~ ~.. directly to the steel framework or by conductors leadlnl~ '~,,;' ~ $-28.1 Anchors. Masonry anchors shall have a through the ridge, roof, or coping walls, or connecte~II '~0 ) diameterofnotlessthan¼in-(6,'Imm) andshallbeset togetherwithaconductorontheexteriorofthebuilding ti:sat is bonded to the steel fra.ncwork. It' :~uch a conductor is employed, it shall be bonded to the steel framework at intervals of not morc than 100 ft (50 m). wire type system in accordance with Chapter 6 or with lightning protection system in accordance with Chapter 5-$2.2 Connections. Connections shall be made on cleaned areas of the steel framework by use of bonding plates with bolt pressure cable connectors having a sur- face contact area of not less than 8 sq in. (5200 bolted, welded or brazed securely to the steel so as to maintain electrical continuity. 3-32.3 Grounding. Ground connections shall be made at approximately every other steel column around the perimeter, and shall not average over 60 ft (18 m) apart. Ground terminals shall be attached to such steel columns. at the lowest available point, with bonding plates having a surface contact area of not less than 8 sq in. (5200 mm'), bolted or welded securely to cleaned areas of the structural steel. 3-32.4 interconnections. Where metal bodies are re- quired to be·bonded elsewhere in this code. the)' need not Chapter ii Protection for Heavy-dury Stacks ii-I General. A smoke or vent stack is classified as heavy-duty if the cross-sectional area of thc flue is greater than 500 sq in. (0,32 m~) and the height is greater than 75 it (25 m). 5-2 Materiah. Materials shall be Class II as shown in Table 3.5 except as described and modified in this chapter. 5-2.1 Corrosion Protection. Copper and bronze materials used on thc upper 25 ft (7.6 m) of a stack shall separately bonded if they are electrically continuous have a continuous covering of lead having minimum thickness of ~, in. (1.6 mm) to resist corrosion by flue bw~th the lightning protection system through the steel framework, gases. Such materials include conductors, air terminals, · connectors, splicers, and cable holders. Stacks that ex- tend through a roof less than 9-5 ft (7,6 m) shall have a lead covering only on those materials above the roof level. ii-3 Air Terminals. Air terminals shall be made of solid copper, stainless steel, or monel metal. They shall be uniformly distributed around the top of cylindrical stacks at intervals not exceeding 8 ft (2.4 m). On square Chapter 4 Protection for Miscellaneous Structures or rectangular stacks air terminals shall be located not and Special Occupancies more than 24 in. (0,6 m) from the corners and shall be spaced not more than 8 ft (2.4 m) apart around the perimeter, 4-1 General. Special consideration shall be given to the miscellaneous structures and special occupancies 3-3.1 Air Terminal Heights. Thc height of air ret- covered in this chapter. All requirements of Chapter S minals above the stacks shall be not less than 18 in. (0.46 m) nor more than 30 in. (0.76 mi. They shall be at least st in. (15 mm) in diameter, exclusive of the corrosion pro- tection. Top-mounted air terminals shall not extend more than 18 in. (0.46 m) above the top of the stack. 5-3.9 Mountings. The air terminals shall be secured to the stack and shall be connected together at their lower end with a lead-covered copper conductor forming a ~--3 Grain, Coal, and Coke Handling and Proce~ing closed loop around the stack. Side-mounted air terminals Structures. On wood frame elevators, provision shall be shall be secured to the stack at not less than two locations. made to allow for the settling and rising of the structure The anchored base shall be considered as one fastening. as grain is loaded and unloaded. For protection from hazards of possible ignition of combustible dust or mix- $-4 Conductors. Conductors shall be copper, weighing tures, refer to NFPA 6lB, Standard for Grain Elet~ators not less than 575 pounds per 1000 ft {558 grams per and BuI~ Grain Handling Facih'ties, and NFPA 65S, meter) without thc lead covering. The size of any wire in Standard for the Prevention of Dust F_~plosion~ t'n Coal the conductor shall be not less than 15 AWG. tXre~aratton Plants. _ ........ ,5-4.1 Down Conductors. Not less than two down con- ~. Metal towers and tanks ~ductors shall be provided. They shall be located on op- ~~ming without ~posite sides of thc stack, and lead from the encircling ~r in'Is as re- ~conductor at the top to ground terminals. Down conduc- ~ided in Chapter 6. ~' tors shall be interconnected at the base of the stack unless individually connected to a common water pipe or metal 4-5 Air=Inflated Structures. structures breeching that will assure the interconnection. Conduc- shall be protected with a mast type or overhead ground tofs shall also be interconnected at intervals of mid- 78 I.It:iiTNINC I,R¢ITI~C'I'-It)N 1' (inF. '1 I I I I I I Fil~rc The striking distance is related to the peak stroke cur- rent lad thus to the severity of the lightning stroke: the c~reater the severity of the stroke, the greater the Striking istance. In the vast majority of cases, the striking distance exceeds 100 ft (30 m). Accordingly. the zone based on a striking distance of 100 ft (30 m) is considered to be adequately protected, The zone of protection afforded by any configuration of masts ot other elevated, conductive grounded objects can readily be determined graphically. Increasing the height of a mast above the striking distance will not in- crease the zone of protection, 6-3.$.3 The zone of protection of an overhead ground wire not over 50 ft (1.5 m) above ground may be taken as a triangular prism or wedge. A prism with a base equal to twice the height (H) of the lowest point of the overhead ground wire is considered to provide protection. (See Figure 6.3.$.1. ) For a ground wire more than 50 ft (15 m) above ground, the zone of protection is based on a strik- ing distance of 100 ft (30 m) and is defined by 100 ft (30 m) radius arcs concave upward. (See Figure 6.3.3.2, ) The supporting masts shall have a clearance from the pro- tected structure as under 6-3,3.4. The ground wire material shall be noncorrosive for the conditions existing at the site and shall not be smaller in diameter than No, 6 6-$.3.4 To prevent side flashes, the minimum distance between a mast or overhead ground wire and the struc- ture to be protected shall be not less than the bonding distance or side-flash distance as determined in accor- dance with Sections 3-23 and 3-!~4. The masts or overhead ground wires shall be grounded and intercon. nected with the grounding system of the structure to be protected. The grounding requirements of Chapter 3 shall apply. 6-3.3.5 Masts of wood, used either separately or with~ ground wires, shall have an air terminal securelyI Zone of Protection for Mast Height 'It" Exceeding 50 Feet (15 m). mounted to the top of the pole (~ Figur~ 6-~. 3.~) and connected to the oundin s stem. As an alternative, an above or across the top of the pole, may be used as the air I terminal, In case of an overhead ground-wire system, the pole guy wire may be used as the down conductor F~ure 6-3.3.5). For metallic masts, the air terminal and the down conductor shall not be required. Air T~mlnll / I Air TTtnll ? Prot~d Stfu~ure Grounding System Interconnlction Figure 6-3.~.5 Alternate Groundin$ Method for Overhead Ground Wire Protection, 6-4 Protection of Specific Classes of Structures. 6-4.1 Aboveground Tanks Containing Flammable Liquids at Atmospheric Pressure. 6-4.1.1 Fixed Roof Tanks. The contents of metallic tanks with steel roofs of riveted, bolted, or welded con- struction, with or without supporting members, used for the storage of flammable liquids at atmospheric pressure are considered to be protected against lightning (in- herently self. protecting) if the following requirements are met: