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RE: "potential impact energy"

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You can use Kinetic energy = Potential energy .5mv^2=mgh
Masses cancel out, which is always exciting, and you solve for the
velocity of the fall.

The average fall arrest force is
(Weight(lbs)Velocity(ft/s))/(Acceleration due to gravity (ft/s^2Time
(s)).

The problem here is the stopping time.  It depends on your fall arrest
equipment and the support structure.  For various lanyards with or with
out shock absorbers the time to stop the fall varies, and can't be
calculated, and must be obtained from the supplier.

Weight is a variable, small thin person, vs large big person with tools.

If suspended from a hi line, the cable deflection also impacts the time
to stop the fall.  So this needs to be added to the calculation.

The fall height H is tricky too.  I try to limit the actual free fall
distance to 2ft, but this has to be balanced against a fall clearance
calculation.  A height calculation making sure the worker doesn't hit
the floor or some equipment below.  This can be 15'-18' from a rigid
support depending on the gear.

The point is to keep the fall arrest force below 1,800 pound for OSHA.
I've added shock absorbers to the cable hi line and demanded shock
absorbers be included in the lanyards.  But check the harnesses the
workers wear, they may be rated for 900.  Check local health and safety
committees having jurisdiction to confirm.

Other liability issues that should be clear are the rescue procedures.
The human body starts to suffer damage in 1/2 to 3/4 of hour of hanging.
So rescue procedures typically need to be ready to go during the work
just in case an incident occurs.

I've seen some rescue procedures where the plan was to use the same high
line to access the fallen worker.  If the high line is rated for one
worker, that can be a problem, and how does one worker pick up another
without some sort of mechanical advantage. - Make sure the lightest
worker is the one on the hi line :)

I hope this provides a good start.
----------------------------
Hans E. Boge, P. Eng.
Boge Boge (1980) Ltd.
268 Ellen Street
Winnipeg MB, Canada, R3A 1A7
p:(204) 942-7276 ext 223
f:(204) 942-7288
www.boge-boge.com
hanseb(--nospam--at)boge-boge.com 

-----Original Message-----
From: Gray Hodge [mailto:ghodge(--nospam--at)hodgedesign.com] 
Sent: Wednesday, October 06, 2004 6:08 PM
To: seaint(--nospam--at)seaint.org
Subject: "potential impact energy"

Can anyone explain to me what is meant by "potential impact energy"?  It
is part of OSHA's fall protection standards.  How do you calculate this?

 

W. Gray Hodge, P.E., S.E. 

HODGE DESIGN ASSOCIATES, P.C.

Structural Engineers

22 Chestnut Street

Evansville, Indiana 47713-1022

812.422.2558 P

812.422.3337 F

ghodge(--nospam--at)hodgedesign.com <mailto:ghodge(--nospam--at)hodgedesign.com> 

www.hodgedesign.com <http://www.hodgedesign.com/> 

 


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