Backyard testing
Mark D. Baker
Captain
Wichita (KS) Fire Department
I just finished reading Chuck Dean`s “Rescue Rope: Lifeline vs. the Bottom Line” (July 1996) and have a few comments to add to his information. By conducting his tests in the manner in which he did (using a figure-8 bight attached to a hook, which weakens the rope), he set up the test to show what the results would be in a worst-case scenario (which is usually how we operate at a rescue or fire scene). The result: He showed that even after a lot of use, the ropes that were tested would still support an NFPA one-person load.
If the ropes in Dean`s tests broke at or near the knot or the attachment site, the break could be attributed to the weakness caused by one or both of these two items. I believe that if he had conducted the test without the figure-8 bight or using a hook as an attachment point, he would have come up with much higher breaking strengths.
When a manufacturing or testing agency conducts these tests, it wraps the ends of the rope around large-diameter drums (four inches or larger diameter) three to four times to prevent strength loss in the attachment point so they are actually testing nothing but the rope`s breaking strength. I have seen some test data done by other agencies on used rope that had been well cared for, using the above technique, and the rope usually had a breaking strength of between 7,500 and 9,000 pounds. This would indicate that some of the used ropes out there would still support an NFPA two-person load.
I want to emphasize that I don`t feel there was anything wrong with Dean`s testing. I just wanted to make the point that a diffferent testing method might have produced even higher breaking strengths than the 4,990 to 5,780 pounds he came up with.
Dean and the rest of us who conduct “backyard testing” have been getting some pretty bad press, even from our own fire/rescue community. The reason: Some believe these testing procedures are not technical enough, are not conducted in a physics lab under controlled conditions, and cannot be reproduced. Well, that is why it is called “backyard testing.” Dean covers this very well at the end of his article by saying, “Use the information derived from this test with caution.” Backyard testing has given us some very valuable information. If we just take it for what it is, we can get a lot of good information from it.
