Keep It Safe and Simple
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 effect the raise or lower? Actually, the answer is “all of the above.”
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 effect 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.
- The available anchors useful in rigging to assist in the evolution
- The number of rescuers on-scene and available to use 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 (ie, pulleys, carabiners, prussik cords), and urgency of the slope evacuation.
While all this sounds like a lot to consider, it actually is 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.”
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:
- Consider the patient, stokes basket and medical gear to be 200 pounds.
- On average, consider each rescuer, plus PPE and gear, to weigh 200 pounds each, 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.
- Estimate the weight to be hauled up that 45 degree slope.Patient plus basket and gear plus four rescuers at 200 pounds/rescuer, or, 200 pounds plus four x 200 pounds equals 200 pounds plus 800 pounds equals 1000 pounds total.
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 somewhat less than the true total weight of all the load.
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 that full weight, plus the friction on the ground surface of the rescuers as they “walk” up the slope. 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 near zero “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.
In keeping with my usual rescue “KISS” philosophy (Keep It Safe and Simple), if the average rescuer can safely haul approximately 75 pounds by firm gloved grip on a dry, one-half diameter static kernmantle rope, 500 pounds divided by 75 pounds/rescuer equals 6.6 rescuers, or seven 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 effect a manual raise, such that at least seven 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 seven of nine). 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 used on the haul line. So, if you rig a 3:1 Z drag MAS, 18 divided by three equals six 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.
There is nothing wrong with using rescuers to create the “human mechanical advantage” 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 or waterfall.