Harnesses & Rope interaction
Published: 01 January, 2007
With the pendulum swinging far to the side of caution, it is prudent to wonder whether the concern over what has come to be termed ‘harness hang syndrome’ is a monumental step toward harness safety, or an overreactive and injurious blow to work at height?
Some believe that it is the work of standards, such as CEN norms and ISO standards, to mandate harness construction and performance, and thereby protect users from ourselves. Experienced rescuers, however, realise that selecting the right harness for use in rigging or rescue work is more than a matter of meeting a standard. While consideration must be given to regulatory requirements, there are performance and use, and even comfort criteria to think about.
Harnesses can be classified into three general types. There are recreational harnesses, fall protection harnesses, and harnesses for work at height. Within these categories there are numerous variations specific to application and fit. All have grown from a foundation in recreational use, but have evolved to fit specific purpose and applications. Harnesses first saw common use in recreational applications, specifically mountain climbing in Europe and the UK. The actual origins of the harness are unclear, and it is debatable whether or not some of the original harnesses were an improvement or not over the old bowline on a coil.
UIAA, the Union of International Alpine Associations, has been writing standards for recreational climbing equipment for decades. Harness standards were based on assumptions related to rope standards, wherein impact forces in a normal fall are limited to a maximum of 12kN.
In their initial evolutions, UIAA standards allowed only full body harnesses for climbing use. In 1995, the Committee For European Normalisation (CEN) reviewed available information and research and in their modern standards altered the position to accept seat harnesses as viable (and even preferable!) for climbing and falling. Attachment points found adequate for the extreme falls undertaken by climbers were front waist and sternal. No data supports the use of rear attachment points, either waist or dorsal.
Where is the research?
Historical references for these types of harness standards are primarily focused on Parachute Harness, Body Belts, and Full Body dorsal attachment harnesses. Neither Seat Harnesses nor Full Body sternal attachment harnesses were even considered in these tests, presumably because harnesses with such attachments were perceived as being for ‘recreational use’. Much of the historically accepted harness related research can be found in Fundamentals of Fall Protection (Sulowski, 1991). Based on this limited information, Full Body dorsal attachment harnesses were identified as the preferred harness type for fall protection in industry. While the Full Body Dorsal attachment is certainly preferable over the simple body belt, this attachment point has limitations for certain types of applications wherein frontal attachment harnesses offer critical features and benefits. One of the studies that had important impact on harness standards was WCLE-53-292, a military parachute research project from the 1950s. This study pertained to the distribution of forces in parachute harness. The general conclusion was that the body can withstand up to 12kN force for a brief moment without sustaining significant permanent damage. This information was used to prioritise design criteria for parachute harnesses. In 1982 a Frenchman by the name Maurice Amphoux undertook to consider these past works in parachute & aviation research. He reported that disabling vertaebral injuries occur at a rate of 6:10,000 in parachutists, raising some question whether this is or is not acceptable in the workplace. He also reported that the best hang scenario was not from the dorsal d-ring, but in a more upright position, with a strap under buttocks. On the other hand, such a strap would increase potential spinal impact during the arrest phase of a fall. From information such as this, it becomes apparent that the best harness choice for suspension may be different from the preferred harness for fall arrest.
Taking a fall:
The Colour Atlas of Mountain Medicine has a very interesting report from Magdefrau, in which he extrapolates from aviation studies to estimate forces on harness points during a fall. He concludes that, given the existing parameters of dynamic climbing rope and related equipment, forces in a climbing fall are unlikely to reach damaging levels. While his conclusion - that an upright feet-down, controlled fall in the sitting position with upper attachment is best - seems reasonable, the foundation of his assumptions (the ejection seat tests) fail to consider that real falls in harnesses do not mimic ejection from an aircraft (i.e. , upright, seated). What design criteria do we have for harnesses in the work and rescue applications in which we use them? Generally we use harnesses in the workplace for one of two things: Fall Arrest or Suspension.
Fall arrest:
Some who are opposed to frontal attachment points on a work harness will assert that a seat harness will ‘break the back of the wearer’ in the event of a fall because the attachment point is relatively centered on the body. This assumes both the legs and the shoulders traveling downward simultaneously. In fact, this is not what happens during a fall. Those who have taken ‘whippers’ in climbing applications, sometimes upwards of 20 feet, have experienced a very different reality. The body normalizes around the attachment point, and in the case of a waist attachment when the head goes down the legs come up, and vice versa... just like a child’s see-saw. Broken backs are rare. When the attachment point is moved higher, nearer the sternum, impact forces are slightly higher because there is less absorption through motion of the body, but there is also a self-righting event that occurs after a fall. Because of the higher attachment, the body hangs in a nearer upright position. It should also be noted that a frontal attachment also helps to prevent the wearer from doing a face-plant into any structural members or obstructions that may exist. Some would say that in the model of a dorsal attachment fall the wearer settles into his harness and is held in a near upright position. Those who have experienced such an unpleasant event in a dorsal attachment harness will attest that this fall is unpleasant, at best. The dorsal attachment causes the falling body to ‘lead with his head’ into any obstructions that may be nearby. To make matters worse, once he is righted he is in a very untenable position - ‘turtled’ comes to mind. He is leaning forward, unable to reach his safety line, and has no option but to await rescue. In this forward-shift position, additional pressure is placed on the diaphragm making it more difficult to breathe.
