Determining the Moisture Content of Soil (Microwave Oven Method) - Soil Properties: Testing, Measurement, and Evaluation - page 53

organic soils and soils containing oils and coal may ignite and
burn during microwave drying. Continued operation of the
oven after the soil has reached constant weight may also cause
damage or premature failure of the microwave oven.

Note 2 —When first introduced, microwave ovens were
reported to affect heart pacemakers, primarily because of the
operating frequencies of the two devices. Since that time, pace-
makers have been redesigned, and the microwave oven is not
regarded as the health hazard it once was. However, it is ad-
visable to post warnings that a microwave is in use.

(4) Highly organic soils and soils containing oil or other contami-
nants may ignite into flames during microwave drying. Means for
smothering flames to prevent operator injury or oven damage
should be available during testing. Fumes given off from contami-
nated soils or wastes may be toxic, and the oven should be vented
accordingly.

(5) Due to the possibility of steam explosions, or thermal stress
shattering porous or brittle aggregates, a covering over the sample
container may be appropriate to prevent operator injury or oven
damage. A cover of heavy paper toweling has been found satisfac-
tory for this purpose. This also prevents scattering of the test sam-
ple in the oven during the drying cycle.

(6) Do not use metallic containers in a microwave oven because
arcing and oven damage may result.

(7) Observe manufacturer's operating instructions when installing
and using the oven.

(8) The placement of the test specimen directly on the glass liner
tray provided with some ovens is strongly discouraged. The con-
centrated heating of the specimen may result in the glass tray shat-
tering, possibly causing injury to the operator.

A representative sample of the moist soil to be tested should be taken
in an amount as indicated in Table 5-1. If cohesive soil samples are
tested, break them to approximately

TEST SAMPLE

⁄ 4 -in. (6-mm) particles in order
to speed drying and prevent overheating of the surface while drying the
interior.

1

Table 5-1 Test Specimen Masses [1]

Sieve Retaining Not More Than Recommended Mass of

about 10% of Sample Moist Specimen, g

2.0 mm (No. 10) 100 to 200

4.75 mm (No. 4) 300 to 500

19 mm ( 3 ⁄ 4 in.)

500 to 1,000