# Question-   School Structural Characteristics

Solution-
1. ## Classroom structure & incoming power line characteristics

The school structure characteristics are shown in Table 1.

Table 1: Palabek secondary school: environment and structural characteristics for the classroom and office

 Input parameter Comment Symbol Value Reference (SANS63205) Ground flash density (1/km2/year) NG 16 Stroke density map from Viasala Structure dimensions (m) Classroom( Block A, B or E)Office( Block C or D) L, W, H 47.19, 7.05, 2.720.61, 7.05, 2.7 Layout diagram of Palabek secondary school Location factor of structure (classrooms are surrounded by tall trees) Isolated structure surrounded by higher objects CD 0.25 Table A.1 LPS None PB 1 Table B.2 Equipotential bonding None PEB 1 Table B.7 External spatial shield None KS1 1 Equation (B.5)

## Table 2: Palabek secondary school: Classroom power line characteristics

 Input parameter Comment Symbol Value Reference Length (m) a LL 1000 Installation factor Buried CI 0.5 Table A.2 Line type factor LV line CT 1 Table A.3 Environmental factor Rural CE 1 Table A.4 Shield of line Unshielded RS – Table B.8 Shielding, grounding, isolation None CLD 1 Table B.4 CLI 1 Adjacent structureFor classroom -For office - None LJ, WJ, HJ 47.19, 7.05, 2.720.61, 7.05, 2.7 Location factor of structure None CDJ 0.25 Table A.1 Withstand voltage of internal system (kV) UW 2,5 Resulting parameters KS4 0,4 Equation (B.7) PLD 1 Table B.8 PLI 0,3 Table B.9 aAs the length Lof  the line section is unknown, L =1000 m is assumed (Clause A.4 and Clause A.5)
1. ## Determining of losses

As a school is an area whereby most of the day a lot of learners and teachers are found, the only loss that will be considered for this study is the loss of human life (L1).

1. ## Definition of zones

The following zones are identified as marked on the layout diagram in Appendix A:

• Zone 1 – outside the classrooms
• Zone 2 – inside the classrooms
• Zone 3 – inside the offices

It is assumed that during a thunderstorm there will be no person in Zone 1 thus the risk component of this zone is negligible. A safety precaution procedure which will be discussed in the latter part of this study will ensure that there are no persons in Zone 1 during a thunderstorm. The distribution of people in the different zones is shown in Table 3 below.

## Table 3: Palabek secondary school: Distribution of people in zones

 Zone Number of people Time of presence Zone 1 0 - Zone 2 50 1200 hrs Zone 3 4 1200 hrs Total nt= 54 -

The factors valid for Zone 2 and Zone 3 are shown in Table 4 and Table 5 below.

Table 4: Palabek secondary school: factors valid for Zone 2

Table 5: Palabek secondary school: factors valid for Zone 3

## Table 4: Palabek secondary school: factors valid for Zone 2

 Input parameter Comment Symbol Value Reference Type of floor Concrete rt 10-2 Table C.3 Protection against shock (flash to line) None PTU 1 Table B.6 Protection against shock (flash to structure) None PTA 1 Table B.1 Probability that a flash to a the structure will cause injury to living beings by electric shock None PA 1 Equation (B.2) Probability that a flash to a line will cause injury to living beings by electric shock None PU 1 Equation (B.8) Probability that a flash to a line will cause physical damage None PV 1 Equation (B.9) Risk of fire Low rf 10-3 Table C.5 Fire protection None rp 1 Table C.4 Internal spatial shield None KS2 1 Equation (B.6) Power Internal wiring Unshielded(loop conductorsin the same conduit) KS3 0,2 Table B.5 Coordinated SPDs None PSPD 1 Table B.3 L1: Loss of human life Special hazard: none hz 1 Table C.6 D1: due to touch and step voltage LT 10-2 Table C.2 D2: due to physical damage LF 10-1 D3: due to failure of internal systems LO - Factors  for persons in zone nz/ nt´ tz/ 8 760 = 50 /54´ 1200/8760 0.12 Page 51 Resulting parameters LA 1.2 x 10-5 Equation (C.1) LU 1.2 x 10-5 Equation (C.2) LB = LV 1.2 x 10-5 Equation (C.3)

Table 5: Palabek secondary school: factors valid for Zone 3

 Input parameter Comment Symbol Value Reference Type of floor Concrete rt 10-2 Table C.3 Protection against shock (flash to line) None PTU 1 Table B.6 Protection against shock (flash to structure) None PTA 1 Table B.1 Probability that a flash to a the structure will cause injury to living beings by electric shock None PA 1 Equation (B.2) Probability that a flash to a line will cause injury to living beings by electric shock None PU 1 Equation (B.8) Probability that a flash to a line will cause physical damage None PV 1 Equation (B.9) Probability that a flash near a structure will cause failure of internal system None PM 1 Equation (B.3) Probability that a flash to a line will cause failure of internal system None PW 1 Equation (B.10) Probability that a flash near line will cause failure of internal system None PZ 1 Equation (B.9) Probability that a flash to the structure will cause failure of internal system None PC 1 Equation (B.4) Risk of fire Low rf 10-3 Table C.5 Fire protection None rp 1 Table C.4 Internal spatial shield None KS2 1 Equation (B.6) Power Internal wiring Unshielded(loop conductorsin the same conduit) KS3 0,2 Table B.5 Coordinated SPDs None PSPD 1 Table B.3 L1: Loss of human life Special hazard: none hz 1 Table C.6 D1: due to touch and step voltage LT 10-2 Table C.2 D2: due to physical damage LF 10-1 D3: due to failure of internal systems LO - Factors  for persons in zone nz/ nt´ tz/ 8 760 = 50 /54´ 1200/8760 10-2 Page 51 Resulting parameters LA 1 x 10-6 Equation (C.1) LU 1 x 10-6 Equation (C.2) LB = LV 1 x 10-6 Equation (C.3)

1.
2. ## Calculation of collection areas

The collection areas are calculated for the classroom and office block as shown in Table 6 and 7 below.

Table 6: Palabek secondary school: Classroom collection areas

 Symbol Resultm2 ReferenceEquation Equation Structure AD Block B – 978 (A.2) AD = L x W + 2 x (3 x H) x (L + W) + π x (3 x H)2 AM – (A.7) Not relevant Power line AL/P 4,00 x 104 (A.9) AL/P= 40 x LL AI/P 4,00 x 106 (A.11) AI/P= 4 000 x LL ADJ/P 978 (A.2) ADJ/P = L x W + 2 x (3 x H) x (L + W) + π x (3 x H)2

Table 7: Palabek secondary school: Office collection areas

 Symbol Resultm2 ReferenceEquation Equation Structure AD Block C - 575 (A.2) AD = L x W + 2 x (3 x H) x (L + W) + π x (3 x H)2 AM – (A.7) Not relevant Power line AL/P 4,00 x 104 (A.9) AL/P= 40 x LL AI/P 4,00 x 106 (A.11) AI/P= 4 000 x LL ADJ/P 978 (A.2) ADJ/P = L x W + 2 x (3 x H) x (L + W) + π x (3 x H)2

1. Calculation of expected annual number of events

Table 8 : Pabalek secondary school: Expected annual number of dangerous events for the classroom

 Symbol Result1/year ReferenceEquation Equation Structure ND Block B – 3.9´ 10–3 (A.4) ND= NG´ AD´ CD´ 10–6 NM – (A.6) Not relevant Power Line NL/P 64´ 10–2 (A.8) NL/P= NG´ AL/P´ CI/P´ CE/P´ CT/P´ 10–6 NI/P 16 (A.10) NI/P= NG´ AI/P´ CI/P´ CE/P´ CT/P´ 10–6 NDJ/P 3.9´ 10-3 (A.5) NDJ/T= NG´ ADJ/P´ CDJ/P´ CT/P´ 10–6

Table 9: Pabalek secondary school: Expected annual number of dangerous events for the office

 Symbol Result1/year ReferenceEquation Equation Structure ND Block D – 2.3´ 10–3 (A.4) ND= NG´ AD´ CD´ 10–6 NM – (A.6) Not relevant Power Line NL/P 64´ 10–2 (A.8) NL/P= NG´ AL/P´ CI/P´ CE/P´ CT/P´ 10–6 NI/P 16 (A.10) NI/P= NG´ AI/P´ CI/P´ CE/P´ CT/P´ 10–6 NDJ/P 3.9´ 10-3 (A.5) NDJ/T= NG´ ADJ/P´ CDJ/P´ CT/P´ 10–6

1. Calculation of Risk

Table 10: Calculation of risk components

 Type of Damage Source of Damage Risk Component Z1 Z2 Z3 Structure D1Injury Lightning flash to a structure RA=ND.PA.LA - 4.6´ 10–8 2.3´ 10–9 4.8´ 10–8 Lightning flash to an incoming line RU=(NL+NDJ).PU.LU - 7.7´ 10–6 6.4´ 10–7 8.3´ 10–6 D2Physical Damage Lightning flash to a structure RB=ND.PB.LB - 4.6´ 10–8 2.3´ 10–9 4.8´ 10–8 Lightning flash to an incoming line RV=(NL+NDJ).PV.LV - 7.7´ 10–6 6.4´ 10–7 8.3´ 10–6 Total R1= 1.6´10–5

BecauseR1= 1.6 x 10–5is higher than the tolerable risk value ofRT= 10–5 a suitable lightning protection system for the school structure is necessary.

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