Agriculture Reference
In-Depth Information
measuring penetration and permeation. Insight into the likely resis-
tance of a PPE material to penetration or permeation can often be ob-
tained by degradation testing.
With regard to chemical transit through PPE and PPE materials, it is gen-
erally true that:
•
No one PPE material is resistant to all chemicals.
•
One cannot predict with certainty the barrier effectiveness of a PPE
material to one liquid on the basis of its performance against another
liquid. Predicting chemical resistance to multi-component liquids,
which many pesticides are, is particularly problematic.
•
Barrier effectiveness increases with the thickness of the material.
•
Barrier effectiveness increases with decreases in air permeability.
•
Comfort decreases with increased barrier effectiveness.
•
Worker acceptance of PPE decreases as comfort decreases.
1.
Measures of Chemical Resistance
a.
Penetration
As defined above, penetration is the movement of a chemical through
holes in the material or fabricated component of PPE. Standard penetration
tests exist and are described below. In general, these tests have been found ei-
ther not applicable or are not practiced by the research community involved in
studies pertinent to protection from pesticides.
b.
Permeation
Permeation rates and breakthrough times are a function of temperature, the
thickness and composition of the test material, and the nature of the chemical
challenge. Each are discussed below.
1.
Temperature
The solubility of a chemical in a polymer and the ease with which the
chemical moves through the polymer network both increase with temperature.
Consequently, permeation rates increase and breakthrough times decrease as
temperature is increased. Most published permeation data were obtained at
20-25
o
C. Since worker exposures to pesticides may occur at higher tempera-
tures, temperature effects must be considered when assessing the effectiveness
of clothing. Breakthrough times for benzene in neoprene were 40 minutes at
7
o
C, 24 minutes at 22
o
C, and 16 minutes at 37
o
C. Over this same range the
permeation rates increased by 74%. British researchers have demonstrated de-
creases in breakthrough times ranging from 3% to 29%, dependent on the
chemical/material pair, as the temperature was increased from 23
o
C to 30
o
C.
