EHS guys may still be standing after the fires described, but only if
the wind didn't blow, since most of the strength will be lost at the
wildfire temperatures quoted.
from a wiki post "At about 550° C (1,000° F) Steel is at 50% Strength
and at about 800° C (1472° F) structural steel loses 90% of its strength"
From ASTM 475 (a standard for guy wires) a 1x7 1/4" EHS single strand
is 0.080" diameter and has a specified minimum breaking strength of
650lbs which works out to ultimate tensile stress of 130,000psi, about
the low end of what would be expected of a heat treated alloy high
strength steel. The alloy or heat treatment aren't specified in the
ASTM standard, just the performance parameters. The fire temperature
will anneal the wire to some lower yield and breaking strengths, perhaps
a 50% or more reduction.
So any EHS guy system exposed to fire of the temperatures mentioned
should be replaced. The Zn galvanizing will also be badly damaged since
Zn melts at under 800F. A tower section exposed to these temperatures
is also suspect, but I haven't seen any specs other than "high strength"
for the steel used.
Grant KZ1W
EHS wire is tempered so if exposed to fire will be annealed to a
fraction of its factory strength.
On 5/26/2014 2:52 PM, W0MU Mike Fatchett wrote:
Sorry to hear of your loss. I am surprised that an Engine crew would
have been in the area with temps so hot. Maybe they got in right
after the flame front?
Having steel at the bottom may also discourage vandalism. Phillystran
is really easy to cut through with a knife. As N2IC said it wouldn't
have mattered with the temperatures of the fire.
Was the area around the tower mowed and cleared of heavy fuels?
How close were the trees and other heavy fuel loads to the tower and
outbuildings. More curious from a Firefighting standpoint than
anything. The books are not always right!
*
At what temperatures do forest fires burn?
*An average surface fire on the forest floor might have flames
reaching 1 meter in height and can reach temperatures of 800°C (1,472°
F) or more. Under extreme conditions a fire can give off 10,000
kilowatts or more per meter of fire front. This would mean flame
heights of 50 meters or more and flame temperatures exceeding 1200°C
(2,192° F).
If you live in an area that could see wildfire check out Firewise.org
for information on how to properly make your home defensible for
wildfire. Get rid of wood piles next to your house, remove the pine
duff or straw and other fuels from around your house and gutters.
Clean your gutters regularly. Be aware if you live on a hill that
there may be what we a call a chimney that will help fuel the fire.
Fires love to burn up hills. In some cases, you can't do enough.
Mother nature does what she wants.
Good luck on the rebuild!
Mike W0MU
On 5/25/2014 12:56 AM, Chuck Smallhouse wrote:
A story for those of you using Phillistran cable for guying a tower.
I was talking to a ham that lives in far N. CA, in area that is
subject to wildfires. A couple of years ago the area had a bad
wildfire that moved in the direction of his QTH, in a somewhat rural
area. Even though the area around his home was quite well cleared,
they couldn't save his workshop where most of his test equipment and
ham equipment was located.
When he returned after a mandatory evacuation and surveyed the damage
, he found that not only was his ham shack destroyed, but also his
guyed tower had fallen over. It turned out that he had guyed it
using Phillistrand and that the fire had burned the guys through and
which resulted in the catastrophic demise of his tower and beams.
I guess that the lesson to be learned is, to at least have the bottom
sections of your guys be of steel cable and not any type of
flammable material, especially if you live in a wildfire prone area.
Chuck, W7CS, with no Phillistrand guys .
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