Rigging Low Angle Rescue Systems


CarolinaFireJournal - Bob Twomey
Bob Twomey
04/14/2020 -

“Low angle” rescue evolutions are those revolutions that are basically performed upon slopes less than vertical. Historically, these rescues are on slopes ranging from 15 degrees up to about 67.5 degrees slope or grade.

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Typical Low Angle Rescue Slope

 

Technically they are raises or lowers performed on any slope not considered vertical, or 90 degrees, which would definitely be considered “high angle” rescues falling into the vertical raise or lower category.

As you can see, the terms “low angle” and “high angle” rescues are relative. Relative to what? The slope or grade? The surface conditions of the particular slope (grass, brush, rock, etc)? The methodologies used to affect the raise or lower? Actually, the answer is “all of the above and more.”

A good example of a “low angle rescue” would be the transport of a patient, properly packaged and in a stokes basket, up a roadside slope, as a result of a motor vehicle accident (MVA), where the vehicle has plunged down an embankment. We will use this scenario later in this article.

An Incident Commander or Operations Officer, when planning how to affect a safe, efficient rescue raise of a properly packaged patient up a slope, would need to consider several factors. Such factors include:

  • Angle or grade of slope (zero degrees being flat [a carry-out] or 90 degrees being vertical, thus a high angle evolution)
  • Surface of the grade (grassed slope, brushy slope, rock face, etc.)
  • Surface conditions of the slope (wet grass, wet rock, loose soil or rock, irregular surface, etc.),
  • Any available and suitable anchors useful in rigging to assist in the evolution
  • The number of rescuers on-scene and available to assist to perform the raise
  • The weight of the patient, rescue attendants and rescue/medical gear
  • Length or distance the patient has to be moved
  • Other factors such as lighting (day or night operation), available rescue rigging equipment besides rope (i.e., pulleys, carabiners, prussik cords, etc.), and urgency of the slope evacuation.

While all this sounds like a lot to consider, it’s actually not. A seasoned rescuer is “sizing up” these factors continuously as patient care is underway, preparing for the actual evacuation. In time and through experience, a rescuer learns to look at factors that will dictate a safe way to perform the evolution safely, efficiently and in the least amount of time. It’s called “scene size-up.”

Three rescuers will be utilized to carry victim while being pulled up the rock face.

Referring now to the MVA described above, you have a 175-pound patient to evacuate up a 100-foot slope, on a 45-degree angle, covered with moderate grass and light brush. Rescue Operations determines that four rescuers will carry the basket and patient as they are pulled up the slope to the top. General rigging specifications dictate the following:

  1. Consider the patient, stokes basket and medical gear to be 200 lbs. (or more if the patient exceeds 200 lbs.)
  2. On average, consider each rescuer, PPE and gear, to weigh 200 pounds, which is reasonable in calculating rigging or hauling. Some rescuers will weigh more, some less, but in general for rigging or hauling, 200 pounds is reasonable.
  3. Estimate the weight to be hauled up that 45-degree slope: Patient plus basket and gear plus four rescuers at 200 pound/rescuer: 200 pounds plus (4 x 200 pounds = 200 pounds plus 800 pounds = 1000 pounds total (includes the weight of the basket, number one above).

If this were to be a strictly vertical raise, you would have 1000 pounds to lift plus “friction drag” through all the components of a mechanical hauling system, if one was utilized. However, this is NOT a vertical raise; it is a raise on an inclined surface. Therefore, what you will be “raising” or pulling up the slope will be a vectored weight somewhat less than the true total weight of all the load. Now, not to get overly technical or to pole vault over peanuts, look at the situation like this: the total weight to be hauled up the slope will be some value less than the total full weight.

An engineer I discussed this with agreed that the rescuers supporting the basket merely walking up the slope as they are being pulled up that slope, would, for practical purposes, generate negligible “friction weight” added to the load. Therefore, for calculating the hauling system needs, you would be hauling approximately one-half of the total load up a 45-degree slope, or 500 pounds. Obviously, the more vertical the slope becomes, the more weight that will be on your hauling system, especially if the rescuers cannot just walk up the slope but must be pulled up the slope with the basket and patient. Therefore, in these situations for safety and simplicity sake, use the full weight of the basket/gear, patient and the rescuers.

Rock Face Low Angle Surface

In keeping with my usual “KISS” rescue philosophy (keep it safe and simple), if the average rescuer can safely haul approximately 50 pounds by a firm gloved grip on a dry, one-half inch diameter static kernmantle rope, 500 pounds divided by 50 pounds/rescuer equals 10 rescuers, needed to perform the raise. Obviously, the more rescuers on the rope, the greater the safety factor when performing the rescue, especially if the rescuers are standing on a wet or somewhat slick surface.

Likewise, should an insufficient number of rescuers be on-scene to affect a manual raise, such that at least 10 are not available to perform the manual raise of the basket, patient, and rescuers, now you know the approximate load to be raised via a rigged mechanical hauling system, plus the maximum number of rescuers to place on the haul line of any mechanical hauling system!

This is called the “rule of 18” for use with a one-half inch diameter rope. (See TR General Ropes, Lesson Two, Anchors and Mechanical Advantage Systems, page 7 of 9). It states that, for whatever mechanical advantage system (MAS) is being utilized, the number 18 divided by the actual achieved mechanical advantage equals the maximum number of rescuers to be used on the haul line. So, if you rig a 3:1 Z drag MAS, 18 divided by 3 = 6 rescuers maximum to be utilized to pull the haul line. This rule is to prevent too many rescuers pulling on a MAS haul line and over-stressing the MAS components.

Low Angle Slope, Rock Face, Sized Up for 3 Rescuers.

There is nothing wrong with using rescuers to create a “human mechanical advantage” or a “manual braking system” needed to perform a rescue, provided that safety and due diligence are observed. Rigging a MAS is a tool in the rescuer’s toolbox when there is a lack of human rescuers to perform this task, or logistically, there may not be enough room to utilize the required number of rescuers, such as on a ledge, confined space, or waterfall. Remember here that sometimes a “change in direction” pulley can be most beneficial to placing rescuers on secure footing for the haul system.

On numerous occasions, either in classes, competitions, or on a few actual rescues, I have observed some of the most well-trained rescuers fall into ‘the tunnel-vision trap.” They “mindset themselves” into thinking that they must use all of the technically advanced skills they have learned (and learned very well) on nearly every rescue mission, instead of taking a few minutes to study the situation (scene size-up), and come up with the safest simple system to accomplish the rescue.

Recently, I observed some highly skilled rescuers rigging a low angle MAS rescue on an approximately 30-35-degree rock face to perform a raise, with six rescuers to carry a stokes basket and patient up the rock, as they were manually hauled up the rock from above. While I am a strong supporter of proper safety backups taught in all rope rescue and rigging classes, 45 minutes into the problem, with all the MAS rigging they decided to rig for this exercise, the patient had not been raised a single foot! In a real rescue, this might be a problem.

Keep your rope rescues and rigging rescues as safe, yet simple, as possible. Yes, do the job right; rig the system(s) you need, including using rescuers as the MAS; employ needed and logical safety systems — but don’t fail to accomplish the mission in a reasonably timely manner. While we did not put the victim(s) in their predicament, we as rescuers must make team safety ALWAYS as our first priority. You can’t help someone else when you are busy dying or getting hurt yourself. Remember: we responded to this rescue call to save life.

Bob Twomey has been in the volunteer rescue service for 46 years, having served on five Rescue Squads from the coast to the mountains. He is currently a member of Transylvania County Rescue Squad, past Chief and Training Chief, an EMT for 45 years, and is an IFSAC and OSFM certified Rescue Instructor. Bob has been active in SAR, Mountain Rescue, and teaches high-level rescue. He is the chief pilot of Wolf Tree Aviation, and flies helicopter searches and rescue support locally. He is a Crew Chief for the NC Forest Service. He can be reached at 828-884-7174 or at [email protected]comporium.net.

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