2017 Annual Conference. Safety Factors

Transcription

1 2017 Annual Conference Safety Factors

2 An Exploration of Safety Factors In Rope Access Systems Mike Januszkiewicz, PE (SPRAT ) (Yon-us-kay-vitch)

3 As an engineer, I am cursed with looking at things and seeing very few things in life as simple. As such, please do not hate on me. I just think a bit differently than some okay, maybe most.

4 Safety Factors In my world, to fully understand Safety Factors can make your head turn round In the world of the normal people, understanding how engineers think as a similar effect

5 Safety Factors Something to think about particularly in how we present them.

6 Safety Factor: a margin of safety, usually expressed as a ratio of material strength to an expected strain/load (Webster). -A ratio of the minimum strength of a system divided by maximum anticipated load (SPRAT Safe Practices, Section 2.35).

7 What is a reasonable SF? 20:1 10:1 8:1 5:1 2:1 3000# 5000# Who agrees? Who disagrees? Who couldn t give a rip? SF = Minimum System Strength / Maximum Anticipated Load

8 What is a reasonable SF? 20:1 10:1 8:1 5:1 2:1 3000# 5000# Who agrees? Who disagrees? Who couldn t give a rip? What does SPRAT suggest? SF = Minimum System Strength / Maximum Anticipated Load

9 What does SPRAT have to say about it? From the SPRAT Safe Practices: Section 3 Requirements for Safe Work Practices 3.4 JSA considerations 3.5 ensure anchors have been evaluated to ensure overall system safety A3.4 Anchors should have safety factors that meet or exceed those required for the ropes. The attachment of the anchorage should at least equal the strength of the system attached to it. Section 10 Rope Access Equipment Static or Low Stretch Ropes shall normally be used for ascending and descending and have a minimum breaking strength sufficient to supply the users desired calculated system safety factor. In no case shall the safety factor for a rope access system be less than 5:1 A An example of calculating system safety factors is as follows: a 68 kg (150#) worker, to achieve a 5:1 safety factor, must work on a system where the weakest link of the system is calculated to be capable of sustaining at least 340 kg (750#). Not sure this is a good example for reasons to be discussed later. Not sure this is a bad example. Section 14 Tools and Work Equipment A14.2 Every effort must be made to prevent tools and equipment from being dropped Safety factor calculations always take into consideration the weight of tools and equipment. Interesting caveat.

10 What is a reasonable SF? 20:1 10:1 8:1 5:1 2:1 3000# 5000# based on 5 X anticipated load SF = Minimum System Strength / Maximum Anticipated Load

11 Is a Safety Factor of 5:1 meaningful? A ratio of the minimum strength of a system divided by maximum anticipated load Example: 5000# / 200# = 25 Thus 25:1 All we really need is a 1K anchor right? 1. What is the minimum strength of a typical Rope Access system? 2. What is the maximum anticipated load? SF = Minimum System Strength / Maximum Anticipated Load

12 Minimum Strength for a Rope Access System Example: Simple Rappel Setup 5000# 5200# 11mm 6000 to 8000# (use 8000#) Slings at anchor 5000# Who agrees? Who disagrees? Who couldn t give a rip? Weakest Link = 5000#? Ref. Petzl

13 Minimum Strength for a Rope Access System Example: Simple Rappel Setup 5000# 5200# 11mm 6000 to 8000# (use 8000#) Slings at anchor 5000# The proverbial fly in the ointment! Spoiler Alert! Think, think, think! Weakest Link = 5000#?

14 Minimum Strength for a Rope Access System Example: Simple Rappel Setup 5000# 5200# 11mm 6000 to 8000# (use 8000#) 11mm Rope with 50%* = 4000# Slings at anchor 5000# * Figure 8: range 60 75% w/ new rope * Figure 8: about 50 % w/ good used rope Weakest Link = 4000# * Reference: Rope Test Lab, New England Rope, Cave.org

15 Minimum Strength for a Rope Access System Example: Simple Rappel Setup 5000# 5200# 11mm 6000 to 8000# (use 8000#) 11mm Rope with 50% = 4000#? Slings at anchor 5000# Slings with angles? (knots, load angles & load multipliers?) Weakest Link = 4000#

16 Load Angles and Load Multipliers Equalizing of loads is the process used to share/distribute a load between two anchors through the use one or more sling(s). Three advantages to using equalizing potential to lower the total load on any one particular anchor, having a second anchor as a backup (should one of the two fail), and the ability to reposition the load. However, care must be exercised. Equalizing inherently creates an angle within the sling(s) that could easily multiply the resultant load to the sling and the anchors. Also, shock loading will occur if one of the anchors fails. R1 R2 Angle Load 90 R1 =.7P R2 =.7P Angle P 120 R1 = P R2 = P 150 R1 = 2P R2 = 2P

17 Minimum Strength for a Rope Access System Example: Simple Rappel Setup 5000# 5200# 11mm 6000 to 8000# (use 8000#) 11mm Rope with 50% = 4000# Slings at anchor 5000# Slings with angles 5000# (by design) (knots, load angles & load multipliers?) Effect of Sling on Carabiner? Weakest Link = 4000#

18 5,200# x 0.80 = 4,160# 5,200# x 0.50 = 2,600#? Oval or Pear? Reference: Highpoint Access & Rescue

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20 Minimum Strength for a Rope Access System Example: Simple Rappel Setup 5000# 5200# 11mm 6000 to 8000# (use 8000#) 11mm Rope with 50% = 4000# Slings at anchor 5000# Slings with angles 5,000# (by design) (remember load angles & load multipliers?) Effect of Sling on Carabiner 4,160# (using 1 HS webbing) Weakest Link = 4000# (rope knot still controls) Minimum System Strength / Maximum Anticipated Load

21 Maximum Anticipated Load What are our anticipated loads? (200#, 400#, 500#?) Worker (220# OSHA 29CFR for lanyards) includes clothing/boots (5 to 15#) Ancillary equipment? (harness, helmet, descender, rope grabs, carabiners, slings...) (10 to 40#) Rope? 200 of 11mm rope = 12# for a 100 rappel (24#, 400 of rope for 200 rappel), (48#, 800 of rope for 400 rappel), (72# for 1,200 for 600 rappel) adds up quick Note: 400 to 600 rappels are not uncommon in some bridge work Maximum Anticipated Load =? SF = 4,000# /? Minimum System Strength Maximum Anticipated Load Minimum System Strength, Maximum Anticipated Load

22 Maximum Anticipated Load What are our anticipated loads? (200#, 400#, 500#?) Worker (220# OSHA 29CFR for lanyards) includes clothing/boots (5 to 15#) Ancillary equipment? (harness, helmet, descender, rope grabs, carabiners, slings...) (10 to 40#) Rope? 200 of 11mm rope = 12# for a 100 rappel (24#, 400 of rope for 200 rappel), (48#, 800 of rope for 400 rappel), (72# for for 600 rappel) adds up quick Note: 400 to 600 rappels are not uncommon in some bridge work Maximum Anticipated Load = 260# (220# + 40#) SF = 4,000# / 260# = 15:1 And we re done! Right? Minimum System Strength Safety Factor Maximum Anticipated Load Minimum System Strength, Maximum Anticipated Load

23 Maximum Anticipated Load What are our anticipated loads? (200#, 400#, 500#?) Worker (220# OSHA 29CFR for lanyards) includes clothing/boots (5 to 15#) Ancillary equipment? (harness, helmet, descender, rope grabs, carabiners, slings...) (10 to 40#) Rope? 200 of 11mm rope = 12# for a 100 rappel (24#, 400 of rope for 200 rappel), (48#, 800 of rope for 400 rappel), (72# for for 600 rappel) adds up quick Note: 400 to 600 rappels are not uncommon in some bridge work Rescue load? (220#) Maximum Anticipated Load = = 480# SF = 4,000# / 480# = 8:1 Now we re done! Right? Minimum System Strength Safety Factor Maximum Anticipated Load Minimum System Strength, Maximum Anticipated Load

24 What are our anticipated loads? (200#, 400#, 500#?) Worker (220# OSHA 29CFR for lanyards) includes clothing/boots (5 to 5#) Ancillary equipment? (harness, helmet, descender, rope grabs, carabiners, slings...) (10 to 40#) Rope? 200 of 11mm rope = 12# (400 for 200 rappel = 24#), 50# (800 of rope) adds up quick Rescue load? (220#) Maximum Anticipated Load = 480# Maximum Anticipated Load We Need To Explore Maximum Anticipated Load A Little More!!! SF = 4,000# / 480# = 8:1 Now we re done? We have a bigger fly in the ointment, there s an elephant in the room that we re ignoring, or there s an 600# gorilla in the room in the room that we re ignoring choose your metaphor. We have a backup rope for a reason. It only looks like I weigh 600#) Minimum System Strength, Maximum Anticipated Load

25 Maximum Anticipated Load Do we truly have a Static System? No Any movement within the system generates some dynamic effect Why do we have that 2 nd (backup) rope? What is the potential Fall Factor? What is the affect of a dynamic drop? In particular, what load can it generate? Minimum System Strength, Maximum Anticipated Load It s not the fall that kills you. It s the sudden stop at the end.

26 An engineer s way of saying: It s not the fall that kills you. It s the sudden stop at the end.

27 Fall Factor: good news and bad news Fall Factor = length of fall divided by the length of the lanyard The bigger the FF, the bigger the load generated.

28 Fall Factor: good news and bad news Potential FF? FF = 1.5? FF = 1? FF = 0.5? FF = 0.25? Backup device even with attachment point Fall Factor = length of fall divided by the length of the lanyard The bigger the FF, the bigger the load generated. Not the whole story!

29 Fall Factor: good news and bad news Fortunately, people much smarter than I have looked into this for us! The good news with rope more rope in the system = longer effective lanyard and rope stretch = shock absorption We aren t usually attached directly to the anchor point. We have a backup system. The backup device and lanyard are parts of that system, but so is the rope and any knots within the system

30 Fall Factor: good news and bad news? The bad news that goes with the good news rope stretch = longer effective fall fall = free fall + stopping distance The flip side stretch = shock absorption We aren t usually attached directly to the anchor point. We have a backup system. The backup device and lanyard are parts of that system, but so is the rope and any knots within the system with enough rope in the system, I could use a Gibbs ascender as a backup device for a 20 foot fall.

31 Maximum Anticipated Load What is a Dynamic load? (Shock Load) (Impact Force) Dynamic Load is defined by an energy equilibrium equation E = Dfall x Wweight = Dstop x Fstop, where D = distance, F = force (weight) Wweight = initial weight of an object (the load we want to support) Fstop = Dynamic-load (force) generated by the falling object stopping = (Dfall x WWeight ) / Dstop Thus... The farther the object free falls, the larger the potential force generated (presuming a relatively short stopping distance). The converse is the longer/farther it takes to stop the object, the lower the final force that is generated. Now that we ve reviewed FF Minimum System Strength / Maximum Anticipated Load

32 Maximum Anticipated Load What is a Dynamic load? (Shock Load) (Impact Force) Dynamic Load is defined by an energy equilibrium equation E = Dfall x Wweight = Dstop x Fstop, where D = distance, F = force (weight) Wweight = initial weight of an object (the load we want to support) Fstop = Dynamic-load (force) generated by the falling object stopping = (Dfall x WWeight ) / Dstop Thus... The farther the object free falls, the larger the potential force generated (presuming a relatively short stopping distance). The converse is the longer/farther it takes to stop the object, the lower the final force that is generated. Example #1: a 10# bowling ball dropped 4 feet onto a concrete floor (stopping distance = 1/16 ) Fstop = 7,500+ # a 10# bowling ball dropped 4 feet onto a mattress (stopping distance = 12 ) Fstop = 40# (This is why system shock absorbers are so important)

33 Maximum Anticipated Load What is a Dynamic load? (Shock Load) (Impact Force) Dynamic Load is defined by an energy equilibrium equation E = Dfall x Wweight = Dstop x Fstop, where D = distance, F = force (weight) Wweight = initial weight of an object (the load we want to support) Fstop = Dynamic-load (force) generated by the falling object stopping = (Dfall x WWeight ) / Dstop Thus... The farther the object free falls, the larger the potential force generated (presuming a relatively short stopping distance). The converse is the longer/farther it takes to stop the object, the lower the final force that is generated. Example #1: a 10# bowling ball dropped 4 feet onto a concrete floor (stopping distance = 1/16 ) Fstop = 7,500+ # (ignoring any bounce) a 10# bowling ball dropped 4 feet onto a mattress (stopping distance = 12 ) Fstop = 40# (See why system shock absorbers are so important) Example #2: a Rope Access Technician (220#) has a FF 1 on a 2 lanyard attached to a rigid anchor point (stopping distance = 5 for a dynamic elongation of 20%) Fstop = 1,050# +/- (for a 2 foot fall) Note: a 24 fall onto a backup device attached to a low stretch rope, anchored to rigid point (using a knot) is a more complex system than being directly attached to a rigid anchor point.

34 Maximum Anticipated Load What is a Dynamic load? (Shock Load) (Impact Force) Dynamic Load is defined by an energy equilibrium equation E = Dfall x Wweight = Dstop x Fstop, where D = distance, F = force (weight) Wweight = initial weight of an object (the load we want to support) Fstop = Dynamic-load (force) generated by the falling object stopping = (Dfall x WWeight ) / Dstop Thus... The farther the object free falls, the larger the potential force generated (presuming a relatively short stopping distance). The converse is the longer/farther it takes to stop the object, the lower the final force that is generated. Example #1: a 10# bowling ball dropped 4 feet onto a concrete floor (stopping distance = 1/16 ) Fstop = 7,500+ # (ignoring any bounce) a 10# bowling ball dropped 4 feet onto a mattress (stopping distance = 12 ) Fstop = 40# (See why system shock absorbers are so important) Example #2: a Rope Access Technician (220#) has a FF 1 on a 2 lanyard attached to a rigid anchor point (stopping distance = 5 for a dynamic elongation of 20%) Fstop = 1,050# +/- (for a 2 foot fall) Note: a 24 fall onto a backup device attached to a low stretch rope, anchored to rigid point (using a knot) is a more complex system than being directly attached to a rigid anchor point. Example #3: a Rope Access rescue (2 person load), FF = 1 on a 2 lanyard attached to a shock absorbing rope grab. What is the Stopping Force?

35 Non-Scientific Drop Test Forces (220# Rescue Randy) Device Fall Factor Rope Slippage Maximum Force Device 1 (2 ) 1 1 (25mm) 1,100 1,200 lbs Device 1 (2) (40mm) 1,800-2,000 lbs Device 1 (5 ) (40mm) 2,250 lbs (10KN) Device 2 (Shunt*) (165mm) 900 lbs (4KN) Device 2 (Shunt*) (470mm) 900 lbs (4KN) Device (12mm) 1,600 lbs (7KN) Device (285mm) Torn Mantel 1,400 lbs (6KN) Device 4 2 Absorber Deployed 900 lbs (4KN) Device 5 2 w/ dyn. cowtail 1 (25mm) 1,400 lbs (6KN) Device 6 2 with 24 fall (610mm) 6 ** (150mm) 900 lbs per bar tack(breaks 2-1/2 tacks/stitches) Device 6 2 with 36 fall (915mm) 12 ** (305mm) 900 lbs per tack(breaks 4 tacks) * Device not currently approved as an industrial rope access device One set of Results for test using Polyester static rope, near anchor, knots pre-tightened.

36 What are our anticipated loads? (200#, 400#, 500#?) Worker (220# OSHA 29CFR for lanyards) includes clothing/boots (5 to 15#) Ancillary equipment? (harness, helmet, descender, rope grabs, carabiners, slings...) (10 to 40#) Rope? 200 of 11mm rope = 12# for a 100 rappel (24#, 400 of rope for 200 rappel), (48#, 800 of rope for 400 rappel), (72# for for 600 rappel) adds up quick Note: 400 to 600 rappels are not uncommon in some bridge work Rescue load? (220#) Maximum Anticipated Load = 480# ( static rescue load) Maximum Anticipated Load =? (rescue generated dynamic load) SF = 4,000# /? =? Minimum System Strength Maximum Anticipated Load Safety Factor Maximum Anticipated Load

37 What are our anticipated loads? (200#, 400#, 500#?) Worker (220# OSHA 29CFR for lanyards) includes clothing/boots (5 to 15#) Ancillary equipment? (harness, helmet, descender, rope grabs, carabiners, slings...) (10 to 40#) Rope? 200 of 11mm rope = 12# for a 100 rappel (24#, 400 of rope for 200 rappel), (48#, 800 of rope for 400 rappel), (72# for for 600 rappel) adds up quick Note: 400 to 600 rappels are not uncommon in some bridge work Rescue load? (220#) Maximum Anticipated Load = 480# ( static rescue load) Maximum Anticipated Load = 900#?(rescue generated dynamic load) SF = 4,000# / 900# =? Minimum System Strength Maximum Anticipated Load Safety Factor 2 person rescue load close to the anchor FF = 1 +/- Note: could be lower or a lot higher!!! Maximum Anticipated Load

38 What are our anticipated loads? (200#, 400#, 500#?) Worker (220# OSHA 29CFR for lanyards) includes clothing/boots (5 to 15#) Ancillary equipment? (harness, helmet, descender, rope grabs, carabiners, slings...) (10 to 40#) Rope? 200 of 11mm rope = 12# for a 100 rappel (24#, 400 of rope for 200 rappel), (48#, 800 of rope for 400 rappel), (72# for for 600 rappel) adds up quick Note: 400 to 600 rappels are not uncommon in some bridge work Rescue load? (220#) Maximum Anticipated Load = 480# ( static rescue load) Maximum Anticipated Load = 900#?(rescue generated dynamic load) SF = 4,000# / 900# = 4.4 Minimum System Strength Maximum Anticipated Load Safety Factor 2 person rescue load close to the anchor FF = 1 +/- Maximum Anticipated Load SF = 4:1

39 Example #3: A Rope Access rescue (2 person load), FF = 1 on a 2 lanyard attached to a shock absorbing rope grab located near the anchor point. What is the Stopping Force? Safety Factor? Fstop = 900# with additional drop (18 + for a really good backup system) SF = 4,000# / 900# = 4.4 SF = 4:1 5:1 Note: That might be below the 5:1 suggested by SPRAT Remember we re using an 8,000# rope. A 6,000# rope yields a 3:1 SF Remember that elephant in the room? Or that 600# gorilla?

40 Example #3: A Rope Access rescue (2 person load), FF = 1 on a 2 lanyard attached to a shock absorbing rope grab located near the anchor point. What is the Stopping Force? Safety Factor? Fstop = 900# with additional drop (18 + for a really good backup system) SF = 4,000# / 900# = 4.4 SF = 4:1 Are you still safe?? Yeah, as long as you don t hit something during the fall & deceleration distance. Note: OSHA declares that a 2:1 Safety Factor for dynamic forces is sufficient. 29CFR (d) Personal Fall Arrest (15) Anchorages used for personal fall arrest equipment shall be independent and capable of supporting at least 5000# (22.2 KN) per employee attached, or shall be designed, installed, and used as follows: (i) as part of a complete personal fall arrest system which maintains a safety factor of at least two; and (ii) under the supervision of a qualified person. 29CFR (16) Personal fall arrest systems (v) have sufficient strength to withstand twice the potential impact energy of an employee free falling a distance of 6 feet (1.8m), or the free fall permitted by the system, whichever is less. 29CFR (e) Positioning device systems (1 5) Strength of Positioning Systems: anchors must be capable of the greater of 2X potential impact load of employee fall or 3000# (13KN), with connectors capable of 5000# (22KN) and free fall limited to 2 ft. max.

41 Things to consider I have only considered a simple system setup in this presentation. An anchor setup and support system can be a very complex matter to analyze. Particularly when considering load angles (re-directs, rebelays, angled rappels ), use of highlines, use of AHD (tri-pods, A-frames, Gin Poles, Luffing Poles ), or any other myriad of optional system add-ons. = Remember that SPRAT Safe Practices example (A ) with the 150# worker? 5 x 150# = 750# Not the best example (3,000# minimum not 750#), but not the worst either (it considers static loads, not forces). 29CFR (d)Personal Fall Arrest (15) Anchorages used for personal fall arrest equipment shall be independent and capable of supporting at least 5000# (22.2 KN) per employee attached, or shall be designed, installed, and used as follows: (i) as part of a complete personal fall arrest system which maintains a safety factor of at least two; and (ii) under the supervision of a qualified person. Dynamic Forces must be considered in any rope access system! We have a two rope system: one for positioning and one as a backup (fall protection). Potential loads are different, but we often treat them the same.

42 Things to consider I have only considered a simple system setup in this presentation. An anchor setup and support system can be a very complex matter to analyze. Particularly when considering load angles (re-directs, rebelays, angled rappels ), use of highlines, use of AHD (tri-pods, A-frames, Gin Poles, Luffing Poles ), or any other myriad of optional system add-ons. = 29CFR (d)Personal Fall Arrest (15) Anchorages used for personal fall arrest equipment shall be independent and capable of supporting at least 5000# (22.2 KN) per employee attached, or shall be designed, installed, and used as follows: (i) as part of a complete personal fall arrest system which maintains a safety factor of at least two; and (ii) under the supervision of a qualified person. The best way to mitigate the affects of dynamic loading limit the potential for dynamic loading. Keep your potential fall factor low! Potential forces diminish as more rope is involved in the system, but there are trade-offs!

43 Safety Factors Is a Safety Factor of 5:1 meaningful? IMHO In the end, you have Static Safety Factors: 5:1 accounts for some unintended dynamic affects (very relevant, maybe even a bit low) Dynamic Safety Factors: 5:1 would seem to be difficult to attain without bumping up the strength (read size) of rope or seriously controlling potential Fall Generated Forces. 5:1 seems to be a bit unnecessarily burdensome (could be considered high, but depends. Again, I don t see much as Simple). I see these safety factors as different, but related. And they likely should be treated differently.

44 You could always run a dual tensioned rope system. But then again, there might be some complications with that too. Particularly with rescue. A discussion for another time.

45 QUESTIONS?