STATISTICAL INVESTIGATION IMPACT OPENING OF MINE SHAFT DETACHING HOOKS

Transcription

1 Anglo Technical Division A Division of Anglo Operations Limited STATISTICAL INVESTIGATION OF THE RISK OF ACCIDENTAL IMPACT OPENING OF MINE SHAFT DETACHING HOOKS De Wet Strydom Johann Wannenburg

2 Presentation outline Introduction Method Dynamic finite element analysis Probabilistic bili simulation Conclusion 2

3 Introduction 1995 Fatal accident at No. 2 Vaal reef shaft Locomotive fell down shaft 104 fatalities Detaching hook detached Rope elasticity was sufficient for rope to survive impact Many lives may have been saved Additional questions concerning the overall risk were raised A number of SIMRAC projects were launched to quantify the risk of an accidental opening 3

4 Introduction Detaching hook configuration Copper shear pin Pivot pin Outer plates Banana slot pin Scissor plates 4

5 Introduction Typical operation of a detachment hook 5

6 Introduction Since 1995, the South African Safety In Mining Research Council (SIMRAC) funded various projects aimed at quantifying and mitigating g these risks Work presented in this paper performed as part of SIMRAC project SIM , with aim to establish methodology for final quantification of risk for each shaft and setting of an acceptable standard. 6

7 Historical work Greenway, Hamashin and Thomas (1996) Crichton and Smith (1997) Wainwright (1997) Wainwright (2001) 7

8 Method Survey Actual hook resistance Monte Carlo Simulation Required minimum Hook resistance Head Impact Analysis 8

9 Dynamic FEA: Model 10 different hooks were modelled d Meshed only with Hex elements Contact was modelled in between all contacting surfaces Rope stiffness to simulate 160m of rope 9

10 Dynamic FEA: Strain rate model Johnson Cook strain rate model: σ y = ( ) ε n & A + Bε + p 1 Cln ε& 0 A=Static ti yield strength th B=Hardening parameter n=hardening exponent C=strain rate parameter Nominal shear stre ess (Pa) Plastic behaviour 7 x M Elastic behaviour Failure point Displacement (mm) x 10-3 Split hopkinson bar 10

11 Dynamic FEA: Friction testing Moving SHB Bolt hole for pretension Stationary SHB 0.18 SHB test set-up 0.16 μk=0.05; μs=0.1 friction coefficient TC061008i - greased - normal = 1618 N - p_max = 752 MPa TC061008h - greased - normal = 4267 N - p_max = 1222 MPa TC061008f - greased - normal = 6718 N - p_max = 1533 MPa shear displacement [mm] 11

12 Dynamic FEA: Failure criteria UCT dynamic ultimate shear tests Plastic strain in FEA is mesh size dependent Use a pragmatic approach: 20-30% shear displacement to diameter ratio resulted in failure Shear displacement 12

13 13 Dynamic FEA: Results

14 14 Dynamic FEA: Results

15 Dynamic FEA: Results Hook Type Size Anti-opening mechanism Velocity of falling mass Kinetic energy of falling mass at impact after impact Energy transferred to hook tons m/s kj kj kj Hook 1 10 Yes Hook 2 10 Yes Hook 3 20 No Hook 4 20 No Hook 5 20 Yes Hook 6 20 Yes Hook 7 20 Yes Hook 8 20 Yes Hook 9 20 Yes Hook Yes

16 Dynamic FEA: Model verification Buxton Tests: Rocket, 750 kg, 20.6 m/s, Buxton #13 Partially released 16

17 Probabilistic Assessment: Modelling logic h? Source Category No. Description No. Descript 1 Rocks coming loose from the sidewalls 2 3 Rocks falling from overloaded skips (spillage), or during tipping at headgear Objects breaking off / coming loose from cages/skips 1 small roc 2 medium r 3 large roc 4 small roc 5 medium r 6 large roc 7 dolley wh 8 guide wh Questionnaire Included mines from Anglo Platinum, AGA and Harmony Information supplied by shaft engineers Analytical solution No numerical integration Included the effect of drag 17

18 Probabilistic Assessment: Modelling logic Energy transfer calculation: Analytical l solution Conservation of linear and angular momentum Conservation of Energy Included friction, angle and point of impact and object angle 18

19 Probabilistic Assessment: Results Probability of cage being released while carrying passengers over a 1 year period for a 20 ton hook Unmodified Anti-opening mechanism 1 Anti-opening mechanism 2 Probability of accidental release over a 1 year period (with persons in cage) Hook # Probability e e e e e e e e e e-6 19

20 Probabilistic Assessment: Results Annual loss of life (according to Cole) Degree of risk Attitude of the voluntary Attitude of the involuntary Typical example Very risky Very concerned Totally Deep sea diving, 1e -2 unacceptable rock climbing Risky Concerned Not acceptable Deep sea diving, rock climbing Some risk Circumspect Very concerned Car accident 1e -4 Slight chance Of little concern Concerned Aeroplane, home accident Unlikely Of no concern Circumspect Public transport accident Very unlikely Of no concern Of little concern Fatality in public place Practically impossible Of no concern Of no concern Failure of nuclear plant Probability 1e -3 1e -5 1e -6 1e -7 1e -8 Worst hook: 44e-6 Best hook: 0.4e-6 20

21 Probabilistic Assessment Anglo Technical Division A Division of Anglo Operations Limited Typical Anglo American fatality statistics

22 Probabilistic Assessment Anglo Technical Division A Division of Anglo Operations Limited South African vehicle accident statistics

23 Probabilistic Assessment Anglo Technical Division A Division of Anglo Operations Limited USA vehicle accident statistics

24 Probabilistic Assessment Anglo Technical Division A Division of Anglo Operations Limited USA vehicle accident statistics

25 Probabilistic Assessment Anglo Technical Division A Division of Anglo Operations Limited Fatal vehicle accident statistics

26 Probabilistic Assessment Anglo Technical Division A Division of Anglo Operations Limited FiF and Probability does not change if number of vehicle changes FiF of 0.15 higher than average FiF for Anglo for all activities

27 Probabilistic Assessment Anglo Technical Division A Division of Anglo Operations Limited From previous assessment: risk to individual of being killed in accident which could have been survived with adequate ROPS = 1.2 e-4 According to Cole: for involuntary => very concerned

28 Probabilistic Assessment ROPS saves lives 28

29 Probabilistic Assessment: Results An average annual probability bilit of a fatal accidental detachment t of a cage per shaft for unmodified hooks is 3.4e-5 The probable number of fatal events that would have occurred over a period of 50 years and 200 shafts: Estimated number of fatal events = 3.4e-5 events/year/shaft x 50 years x 200 shafts Estimated number of fatal events = 0.34 One fatal event happened in SA in the past 50 years, which could be construed as verification for the analysis, but incident involved a locomotive which was not included in the assessment Result is not overly conservative 29

30 Probabilistic Assessment: Interpretation Risk assessments should be done per shaft Illustrative example: Typical value for FIFR = 0.01 fatalities per man hours Improvement factor of 5 Contribution factor of 0.1 Improve overall safety of shaft Don t want shaft travel to be amongst higher risk operations Accidental opening not the only risk associated with shaft travel Target FIFR for accidental openings = FIFR 5 x 0.1 =

31 Probabilistic Assessment: Interpretation Illustrative ti example (continued): Max. allow. annual prob. = x x 0.2 x Max. allow. annual prob. = 3.5e-6 Hook # Probability Anti-opening mechanism Target Number FIFR Number of for people accidental of people Assumed travelling travelling Number hours a cage Normalize of in in a working shaft cage per daily result days person in to a 200 year openings at a time typical 1 shaft per day 0.88e man hours Yes e-6 Yes e-6 No e-6 No e-6 Yes e-6 Yes e-6 Yes e-6 Yes e-6 Yes e-6 Yes 31

32 Conclusion A method has been developed d to determine the probability bilit of accidental opening of safety detaching hooks and the probable number of consequent fatalities over any given period and for any given shaft. The risk of accidental opening of a detaching hook in any shaft, with possible consequential deaths, can now be evaluated. The risk of a falling object accidentally opening a detaching hook and causing the cage can be minimised and managed. A limit on the acceptable level of risk has been proposed. The probability of a cage being accidentally released with persons in it over a 1 year period for any shaft should not be more than typically 3.5e-6 (subjected to site specific assessment). The specification cat for detaching hooks has been updated to include the findings of this study. Based on this study, some hooks will have to be modified to comply with the new spec, depending on the shaft configuration. 32