Evaluation of Wildland Fire Chemicals
Standard Test Procedures
The viscosity, or resistance to flow, of a material can be determined
by a rotational viscometer. The viscometer can also be used to approximate
other flow characteristics by relating viscosity and flow for a known
Because the specific rotational speed and the spindle used
as well as the temperature of the test sample can have a significant
impact on the value determined, it is best to use the same conditions
a test series. To ensure that this is possible, the viscosity should
be measured with all usable spindles.
The viscosity of long-term retardant
products is normally measured using a #2 spindle for products having
viscosity between 1 and 500 centipoise (cP) and a #4 spindle for
products having a viscosity greater than 500 cP; although the #3
spindle may also
be used when the upper values are expected to be less than 2,000 cP
- Brookfield model LVF viscometer and spindle set
in a straight-sided container with an inside diameter of 2
inches or more.
- Level the viscometer by adjusting the feet and/or rotate the viscometer
on the mounting shaft until the bubble is centered before each
- Set the speed control to 60 rpm; 60 should be on the upper
surface of the knob found on the left side of the housing.
the sample and container under viscometer.
- Measure and record
of the sample.
- Select a spindle appropriate for the
viscosity to be measured.
The number of the spindle is engraved at the top of each
- Screw spindle onto the viscometer.
- This is a
should be finger tightened only, holding onto
the shaft to prevent movement of the gauge needle, and gently
- NEVER pull down on
- Using the adjustment knob on the viscometer stand, carefully
lower the spindle into the sample to the immersion mark etched
into the spindle shaft.
- With one hand depress and hold the
brake, found on the back of the viscometer head, firmly down
while turning on the viscometer.
- Release the brake once
the viscometer is rotating smoothly and time for 60 seconds.
the brake firmly and turn the viscometer off while continuing
to hold the brake down.
- This keeps the dial indicator
in place until the value can be read.
- If the dial
indicator cannot be seen in the gauge window, turn the
and off quickly
until the needle comes into view, maintaining firm
pressure on the brake.
- Read and record the value on
gauge. Also record the number of the spindle used.
- Refer to the table below to obtain the correct
multiplier for the spindle used.
- Calculate the
centipoises by multiplying the meter reading by
the multiplier corresponding to the particular spindle used.
||Multiplier for Readings at 60 rpm
||1 to 100 cP
||50 to 500 cP
||400 to 2,00 cP
||1,000 to 10,000 cP
|Long-term retardants have typically been measured
using a #2 spindle for viscosities up to 500 cP and a #4 spindle
for viscosities greater than 500 cP.
the viscometers cleaned and calibrated by the manufacturer or other
approved service company at least once a year.
- American Society for Testing and Materials. Standard Test Methods
for Rheological Properties of Non-Newtonian Materials by Rotational
(Brookfield type) Viscometer; D2196-05.
- National Wildfire Coordinating
Group and USDA Forest Service. Lot Acceptance, Quality Assurance,
and Field Quality Control for Fire Retardant Chemicals, Sixth
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