Ultraviolet Testing of Seaman Corporation
FiberTite® Membrane
The sun bombards the earth with radiant energy on a daily basis. This radiant energy appears in a variety of forms including X-rays, gamma rays, cosmic rays, infrared, ultraviolet and visible light. The difference between the energy forms is their wavelength or the measured distance between the peaks of their individual wave patterns. The peaks can be measured in kilometers (thousands of meters) to less than a nanometer (one billionth of a meter). Ultraviolet light only makes up about 5% of the total sunlight that falls on the earth, but it contributes more to the degradation of single-ply membranes than any other weather related element.
Radiant energy within the visible light spectrum ranges between 400 nm to 760 nm. The ultraviolet light spectrum consists of radiant energy between 280 and 400 nm. As the wavelengths within the spectrum get shorter, the radiant energy increases to the point that it can split the bonds of chemical substances and produce changes within the materials. Fortunately, our atmosphere absorbs the greater part of the shorter wavelength radiant energy. Radiation below 300 nm, which would include shorter UV rays, X-rays, gamma rays and cosmic rays, is almost completely eliminated by the atmosphere. However, a small amount of UV energy between 300 and 400 nm does slip through. This is a relatively small amount of “long wave” ultraviolet light, but there is still enough radiant energy remaining to break down the bonds within the polymer chains that create the backbone of single-ply membranes.
There are quite a few test procedures and apparatuses available to accelerate the effects of UV on single-ply membranes. Although these “weathering devices” can generate relatively fast comparative data, the results should not be construed as actually forecasting a measurable life expectancy for a given product.
Seaman Corporation has used three principle laboratory test procedures to evaluate FiberTite and other outdoor fabrics for UV resistance. The three test procedures utilize criteria as established by The American Society for Testing and Materials (ASTM). They are:
ASTM G153 Carbon Arc (Supersedes ASTM G23) Membrane samples are exposed to twin carbon arc lamps with cyclical water spray. The testing usually takes between 2,000 and 5,000 hours. Used in laboratory testing since 1918, it only produces small amounts of ultraviolet radiation below 350 nanometers. Consequently, it provides poor correlation on membranes sensitive to the shorter UV wavelengths. FiberTite EIP Compound: 8,500 hrs No Cracking
ASTM G155 Xenon Arc (Supersedes ASTM G26) The test utilizes long-arc, water cooled xenon lamps. The light and heat radiance are controlled to a pre-determined level. The test procedure also utilizes a cyclical water spray. Xenon arc does a fair job at simulating the entire sunlight spectrum but does emit some unrealistic short wave UV radiation between 280 and 300 nanometers. FiberTite EIP Compound: 14,000 hrs No Cracking
ASTM G154 QUV (Supersedes ASTM G53) Testing utilizes fluorescent lamps that produce controlled, concentrated ultraviolet wavelengths combined with alternating condensation cycles for a more realistic source of moisture than the water spray used in the other tests. Seaman Corporation has tested FiberTite using two different fluorescent lamps.
UV-A : Provides excellent simulation of the sunlight’s shorter UV radiance from 370 down to the solar cut-off of 295 nanometers. FiberTite EIP Compound: 14,000 hrs No Cracking
UV-B: Provides ultraviolet output below 295 nanometers. UV-B lamps accelerate the testing but the results can be somewhat anomalous. FiberTite EIP Compound: 8,500 hrs No Cracking
In addition to laboratory testing, Seaman Corporation had FiberTite evaluated for UV resistance under ASTM E838. Better known as the Emmaqua Testing (Equatorial Mount with Mirrors for Acceleration with Water), the procedure utilizes a reflecting solar concentrator and mirrors to focus Arizona’s natural sunlight onto the membrane sample. The amount of focused sunlight is equal to about eight (8) suns. The test apparatus also follows the sun’s movement across the sky to optimize exposure. Eight suns can generate an inordinate amount of heat on the sample. The heat is drawn away from the membrane and the sample is subjected to an intermittent water spray. The Emmaqua results are reported in Langleys. As measurement of the sun’s total radiant energy from 300 nm to 3000 nm, one Langley equals 1 gram-calorie per square centimeter. One method of correlating this to actual environmental exposure is to convert Langleys to MJ/m2 (Mega Joules per square meter). One Langley equals 0.04184 MJ/m2. We can complete the correlation by looking at the climate profile for South Florida, which has a typical annual solar energy of 6,588 MJ/m2 or 157,457 Langleys. Arizona’s annual solar energy is approximately 8,004 MJ/m2.
FiberTite’s Emmaqua testing totaled 3 Million Langleys over a two-year period with a total radiation of 125,520 MJ/m2. The following are the inspection results of the membrane upon completion:
Fair Fair As Received As Received
Sunlight is only one aspect of weathering. Temperature, moisture, chemicals and biological elements also contribute to thousands of roofing failures annually. No single device or test procedure can reproduce all the variables whether geographically or within the rooftop environment.
Without a doubt, the most accurate method of determining a single-ply membrane’s resistance to the effects of long-term exposure to the sun’s ultraviolet light is in-place, real time testing on the roof top. This is an area where Seaman Corporation’s FiberTite membrane has excelled. Our historical record provides an excellent testimony for FiberTite Roofing Systems still performing in diverse yet intense UV environments. They include 17-year-old roofs in Southern Florida, 12-year-old roofs in the mile high Denver Colorado area, and 11-year-old roofs in the Arizona desert.
