Rope Rescue and Rappelling. What is the difference?admin
We often hear a lot of confusion over the terms ‘rappelling’ and ‘rescue’. What is the difference? In simple terms, rescue is a way to help someone from a dangerous situation. Rappelling, or abseiling, is an access method. Rappelling is a way to use equipment to go from a higher position to a lower position. Rappelling can be a form of self-rescue to get yourself out of a dangerous situation but when helping others it is normally only part of a rescue.
Why do rescuers rappel?
Rappelling is commonly used for both work and recreation. It is used as a part of rope access work to get to or from a difficult location such as the side of a building. It is commonly done recreationally as a part of rock climbing, canyoneering, or other outdoor activities.
For rescue work, it can be used to quickly access an injured person to determine the extent of injuries to a patient. Rappelling is a good choice to gain quick access since less equipment needs to be setup resulting in faster initial contact with the patient. Once the rescuer makes contact, the patients condition can be communicated back to a team that can then use this knowledge to better prepare for a rescue.
In the case of a person who isn’t injured, or who is lightly injured, a tandem rappel can be performed. In this type of rappel, the rescuer connects to a patient and they both go down together with the rescuer controlling the descent.
This technique is simple for a straight vertical drop but on uneven terrain can be difficult. Balance becomes a problem since the rescuer’s hands are not free as they must be used to control the descent. This slows progress and increases the chance of injuries to both the patient and rescuer.
How is a rappel performed? What Is A Descender?
A descender, or descent control device (DCD), is commonly used to convert the energy of the rappel into heat through the use of friction. The law of conservation of energy, also known as the first law of thermodynamics, states that energy can not be created or destroyed. It can only be changed from one form to another. In order to rappel, the energy of the descending person must go somewhere. If it does not, the person will fall uncontrollably to the ground.
Using a device to safely descend might sound simple but there are variables that must be considered. This includes the persons weight and the length they are descending. The equipment used must be matched to these variables or the descender will not function properly. In this case, the hand gripping the rope will become a major source of friction used to control the descent.
Testing was done by one manufacturer which showed descenders regularly heating to over 100C (212F) during very fast rappels from 45 meters (150 ft). This heat created by the descent is absorbed by the descender where the rope is in contact and then spreads into the rest of the descender as well as the air surrounding the device.
In the case of an improperly chosen descender, much of this heat will be transferred instead into the rappeller’s gloved hand which can result in serious burns. In a worst case scenario, the person will not have enough friction to control the descent resulting in serious injuries and potentially death from falling to the ground.
Types of Descenders
A non-locking, or non-blocking, descender provides friction by creating points of contact with the rope. These multiple points of contact with the rope each create friction which transfers energy allowing a person to control the speed they are descending and prevent them from getting injured. These types of devices usually have a simple construction which uses no, or very few, moving parts.
A self-locking, also known as blocking, descender contains a mechanism which causes the rope to stop in position if hands are removed. This mechanism is usually in the form of a cam which pivots to control the amount of pressure applied to the rope. This type of device is more expensive but much safer since it removes chances for human error.
Descenders used for rescue and work at height generally fall into a number of standard categories:
Figure 8 style devices: Figure 8 style descenders were first invented in the 1930s. They got their name because most of them look similar to the number 8. The rope passes through the device and the rope contact with the metal frame creates friction.
Rack style devices: Rack style descenders have multiple bars that the rope weaves through. The number of bars and the spacing between them determines how much friction is created by the rope passing through them.
Handled descenders (bobbin): In handled descenders, the rope passes around a cam which is manipulated with a handle. Changing the position of the handle moves the cam adjusting the pressure on the rope. This allows friction to be adjusted as needed. Some of these devices include a ‘panic stop’ which stops the rope from traveling through the device if the handle is pulled too hard.
Which descender is right for me?
To ensure safety, descent devices must be chosen based on their intended use. The correct device for use by a rope access professional differs greatly from a recreational climber.
A larger descent device will stay cooler longer since they have more mass to absorb the heat and more surface area to dissipate it. Small descenders have less mass and will become hotter. A device suitable for a 200 meter rappel in a cave will be designed very different than one intended for a 10 meter fire fighter escape system.
Descent devices must also be matched together with other equipment that is being used. Handled descenders are very specific on the size of rope that can be used in them. Figure 8 and rack style descenders can be used with a greater range of rope sizes. Proper use is also effected by the type of rope being used and it’s construction.
The correct descender for rappelling depends on the type of activity that is going to be performed and the ropes being used. For the descender to work properly, the descender must be matched to the expected use. For more information on which descender is right for your needs, please contact us.