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Evaluation of Wildland Fire Chemicals
Standard Test Procedures (revised 5/15/06)

STP 8.2—Wetting Test—Drave's Skein

Summary:

The wetting ability of a foam solution is a measure of its ability to wet and penetrate woodland fuels, such as charred wood, scorched duff, as well as weathered building materials.

This test appears to be more sensitive than surface tension or it measures slightly different characteristics and can frequently differentiate between products with the same or similar surface tension.

Equipment:

  • Cotton skein (Drave’s skein), weight corrected to 5.0 g ± 0.05 g
  • 1.5-g copper S-hook
  • 50-g cylindrical weight
  • Braided Dacron fishing line; 1.5-2 inches
  • 500-mL graduated cylinder; or other tall container deep enough to contain skein
  • Solution of the test product
  • Large syringe or poultry baster
  • Stopwatch

Method:

  1. Correct the weight of each skein to 5.0 g ± 0.05 g before using.
    • Cut one skein apart and use the individual threads to correct other skeins.
    • Use gloves or tongs to handle the skeins when possible.
    • Caution: The oils from skin and residual hand creams can contaminate the skeins and may increase the sink-time.
  2. Using a small loop of the fish line, connect the S-hook to the cylindrical weight.
  3. Prepare a solution of the test product at the test concentration.
  4. Fill the graduated cylinder with test solution sufficient to completely cover the skein assembly.
    • Pour solution slowly down the side of the cylinder to minimize amount of foam created on surface.
    • Allow air bubbles created during pouring to settle out. Any foam that has formed on top should be removed carefully with the poultry baster.
  5. Attach a folded skein to the S-hook and weight.
    • Fold one skein, weight adjusted to 5.0 g, in half so that it is about nine inches long.
    • Ensure that all the threads are contained in the hook.
    • Cut through all of the thread strands at the unattached end of the skein, ensuring that no threads used to tie the skein together or correct the weight are cut.
  6. Holding the skein at the top with the hook and weight dangling, drop the assembly into the foam solution in the graduated cylinder.
  7. Measure the time for the skein to sink.
    • Start timing as soon as the weight hits the bottom of the cylinder.
    • Stop the timer when the S-hook falls, hitting the 50-g weight.
    • If the weight is not level in the cylinder, stop timing as soon as the bottom of the S-hook sinks past the top of the weight.
  8. Record the time, in seconds, for the skein to sink.
    • Occasionally, in weak solutions, the skein will not sink.
    • If there is no sinking after 3 minutes, record the time as "NS" (for "no sinking").
  9. Discard the solution and skein.
  10. Repeat steps 2 through 9, three times using fresh solution and a new skein each time.
  11. Average the results of the three trials, record the average.

References:

American Society for Testing and Materials. Standard Test Method for Evaluation of Wetting Agents by the Skein Test; D2281-68(2005).


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