Line Burn

Q:

 

What is line burn, and how can I avoid the problem?

A:
Line burn is pretty much just what it sounds like: heat-related damage to the nylon components of a parachute system. The term is an all-encompassing description of damage caused when a suspension line pulls rapidly across nylon, generating intense heat and causing a burn to the contact point on the parachute material, associated nylon tapes, other suspension lines, risers or even the harness and container.

The burns usually have one of two causes:

  • Friction created during the deploy-ment and inflation of an improperly packed parachute
  • Friction created when two jumpers collide under canopy

Incorrect packing is the most common source of line burn. If some part of the canopy material moves rapidly across one of the suspension lines (or vice versa) during deployment and inflation, the friction can quickly generate enough heat to damage the canopy material, suspension line or both. Also, line-to-line damage occurs if two lines rub together hard enough. If you find line-burn damage on your canopy or one of your suspension lines, it’s a good idea to carefully inspect the entire canopy and all of the suspension lines for additional damage. Something had to rub together to cause the damage, so there may be more that’s not immediately apparent.

This photo shows line burn to the nylon fabric surrounding a slider grommet. Photo by David Cherry.

Nylon canopy material and the various types of suspension line all have different melting points. Nylon melts at 417 degrees Fahrenheit, which is a lower melting point than all of the common suspension-line types except for Spectra, which melts at 297 degrees Fahrenheit. So, if your canopy is lined with Spectra and you find line-burn damage to the canopy material, there is likely damage to the suspension line, as well. Kevlar, High Modulus Aramid (HMA), Vectran and Dacron lines melt between 932 degrees Fahrenheit (Kevlar) and 482 degrees Fahrenheit (Dacron). So, the more heat-resistant lines may not melt even if they damage the canopy.

You can avoid line-burn-related damage by following the manufacturer’s packing instructions. While packing, keep the suspension lines in the center of the pack job, the slider properly placed up against the slider stops and spread out between the line groups, and make sure the canopy stabilizers are clear of any suspension lines. Those three simple things will go a long way toward preventing damage during inflation.

Canopy collisions can also lead to line-burn damage, and not just on the parachute and its components. A suspension line that’s under the load of a person’s weight is sure to leave a mark or two if it’s pulled across any part of your body during a collision! Plenty of canopy collisions have resulted in burn damage to jumpsuits and skin. If you have a collision of any type, careful canopy and suspension-line inspection will be necessary.

Burns to suspension line material, as shown here, can be difficult to see. Many jumpers discover the damage by running their fingers along the lines. Photo by Clint Vincent.

It is easy to identify line-burn damage and differentiate it from a tear caused by contact with a sharp object. Line burn will cause searing on at least one edge of the fabric at the damage point. Burned lines will appear melted where the friction and heating occurred. On heavier materials, such as that used for container flaps, damage can range from what looks like a light scuffing or discoloration to more extensive burning that you can easily see during an inspection.

Canopy patching and replacement of the damaged suspension lines will easily repair most line-burn damage, but it’s probably a better idea to pack carefully and avoid running into other canopies. Most riggers already have plenty of work to keep them busy. No need to add to the workload!

—Jim Crouch | D-16979
USPA Director of Safety & Training

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