Safe Maximums for Rope Rescue

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Permalink Reply by J Brooks on April 15, 2009 at 8:08pm

What sort of angles are you referring to?

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Permalink Reply by Paul Montpetit on April 15, 2009 at 8:14pm

Angles...? What do you mean...? If it is a "High Angle" team then there are no limits.....if it is a "Technical Rescue" tesm then I believe it is like 60 degrees....15:1 asafety refers to the stress or load that you might encounter....for example for say 2 rescuers and a victim the combined weight might be 550 lbs...then you would ensure that ALL your equipment were rated for at least ...8,250 lbs....Note that includes and carabiners used in the link....Paul

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Permalink Reply by Joe Smith on April 16, 2009 at 2:49am

What I am referring to is during a slope rescue there are critical slope angles where you must use <4 rescuers, or <3 rescuers or <2 rescuers... I know this can be calculated, as different angles will absorb different amounts of the load force into the ground, not all on the system.

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Permalink Reply by Ben Waller on June 21, 2009 at 9:06am

Joe, that's not the case. The slope doesn't dictate the number of rescuers. If the patient doesn't need medical care and the slope isn't obstructed, you don't need any rescuers on the litter.

If you're referring to the number of rescuers pulling on the haul system rope, if you don't have enough, just engineer enough mechanical advantage ratio that the ones you do have can raise the load. In other words, if a 3:1 isn't enough, piggyback a 2:1 on it and you end up with a compound 6:1 system.

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Permalink Reply by Paul Montpetit on April 16, 2009 at 4:49am

Actually Joe it isn't the angle that mandates number of people involved...it is the rescue itself....at a minimum You need a TRO, a safety, a rigger (or 2) at least 1 rescue man (again 2 better) then you need people as line haulers (these donot need to be trained people as your rescue team can direct them)Thers is a lot of work involved in a rope rescue...so having a good supply of TRAINED people is an asset not a liability...as long as the TRO maintains control......Paul

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Permalink Reply by J Brooks on April 16, 2009 at 9:42am

I agree, if we are evacuating a small child, 2 is enough no matter the angle. If it is a 400# monster, then we will need a lot more. The more people that you get atttached to the basket to assist in the rescue, the more coordination that is required to prevent everyone from tumbling over. Use what is need and what can be doen safely. Clear as mud I know. We typically do not use more than three unless absolutely needed to tend a basket. You can put one on each side and one at the foot. This allows a very controlled ascent and carry as long as the haul team is on the ball as well.

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Permalink Reply by Joe Smith on April 16, 2009 at 2:24pm

Hmmm... I'm thinking you guys are not understanding what I am putting down...

In theory during a straight vertical raise, you cannot put more than one rescuer and one patient on the end of the line (based on 300# persons) without exceeding the safety factor...

If the system is on completely horizontal ground, you could have 10 rescuers and 1 patient, because all the load is being carried by the ground and not the rope system...

So that being said, as the angle of the slope increases, the force on the system should increase and the force on the ground should decrease... as the force on the system increases, depending on the number of rescuers attached to the end of the line, you could be exceeding the safety factor.

Reasonably the more horizontal the terrain, the more rescuers you want on the stretcher, as they are required to do more work to keep the stretcher off the ground, this is because they become the load bearing interface... In the vertical environment you only need one rescuer with the stretcher, as he is not carrying any load, the rope is, his whole job is to keep the litter from hanging up on the wall and tending to the patient.

One last quick reference... with my mountain rescue team we use all 11mm rope and 10:1 safety factors...
at <20 degrees we can have a 6 person load,
5 person at <24 degrees,
4 person at <30 degrees,
and 3 person at <42 degrees...
these include the patient (and yes these are guidelines,as there is fancy rigging you can do to get round it)!

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Permalink Reply by Ben Waller on April 16, 2009 at 3:21pm

I've never seen these angles calculated, and in the real world, you rarely have a smooth slope for this type of evacuation anyway. The rule of thumb I use is to put enough people on the system to carry the litter - a minimum of 3 for a small child, 4 for an average-sized adult, and 6 for a large (or larger) adult. We always use a redundent belay for slope evacuations as well as high-angle.

The bottom line is that if the rope is carrying the load, one or two litter attendents are usually sufficient. If the people have to carry the load, then most of the weight is transmitted into the ground through their boots, and isn't carried by the rope. The percentage each part carries will change every time a rescuer moves one of their feet, every time the slope becomes irregular, or every time an obstacle is encountered.

If you need to do a slope evacuation with a really heavy patient, use a slick litter such as a rescue SKED or a plastic stokes litter and use the haul system to sled them up the slope instead of having a rescue team carry them. If a patient attendent is needed, an extra fixed rope can parallel the haul system and the attendent can self-belay up the additional rope with a prussic or with an ascender.

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Permalink Reply by J Brooks on April 16, 2009 at 9:32pm

I had never seen this before and I have a "Guru" in my area that does National level teaching a lot lately. He does all sorts of strength and breakage testing, this has never come up. We severely over engineer all of our systems anyhow. And then we make the redundant. I have yet to really have a system that has been questionable when rigged correctly. All of our gear is G rated, that is basically bomb proof unless something very catastrophic happens.

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Permalink Reply by Ben Waller on June 21, 2009 at 9:02am

You are exactly correct. My personal rule of thumb, as I explained to Jeff below, is to use a four-person carry team for slopes up to 45 degrees. Most of that load is transmitted to the ground the rescuers stand on through their feet, not to the rope system.

If the slope exceeds 45 degrees, reduce the load by eliminating the big litter carry team.
Just use a plastic stokes, rescue SKED, or other slick-bottom litter as a sled and slide it along the ground. If the patient needs care during a steep-angle move, a single attendant rigged into the system near the patient's head can generally take care of it. That single attendant can also manually lift the head of the litter over small obstructions along the way up the hill.

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Permalink Reply by TrainingTECH1 on June 18, 2009 at 2:29pm

Are you the same person who posted a similar question on Firehouse.com?

I responded to a similar question. It can be calculated using trig calculations.

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Permalink Reply by Ben Waller on June 18, 2009 at 11:33pm

Jeff, the trig calculations aren't completely accurate in the real world unless you have a completely smooth slope and the rescuers never pick up their feet. Otherwise, you have a varying load every time you move the litter over an uneven spot and a varying load every time a rescuer takes a step.

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