Average Retentions per AWPA Required Assay Zones and Penetration Depths for Species and Products

AWPA Minimum Preservative Assays and Penetrations

Calculations of Treatable Fractions

CCA-Treated Product Information

Assay Zone

Penetration

Representative Size (in)

Untreated size (in)

Treatable fraction

Commodity

Product

Species

Use Category

≤2" thick

>2" thick

<5" thick

≥5" thick

Thick/Dia

Width

Thick/Dia

Width

Sawn

Sawn Product

SP

all

0.0

0.6

0.0

1.0

2.5

or

85%

2.5

or

85%

1.5

5.5

0.3

4.3

84%

Spruce, SPF West

all

0.0

0.6

0.0

0.6

0.4

and

90%

0.5

and

90%

1.5

5.5

0.3

4.3

84%

Decking

HF, DF, LP

3B

0.0

0.2

0.2

and

90%

1.25

5.5

0.85

5.1

37%

Posts

Round building

SP

≤10" dia

>10" dia

4B

0.5

2.0

0.5

and

90%

2.5

and

90%

10

dia

5

dia

75%

DF

4B

0.25

1.0

Other & Modified farm

SP

4B

0.0

1.0

2.0

or

85%

6

6

4

4

56%

LP

4B

0.0

1.0

1.25

or

85%

6

6

4

4

56%

Crossties

Crossties

DF

4A, B, C

0.0

0.5

0

0.5

90%

7

9

6

8

24%

Poles

Poles

SP

4A, B, C

0.5

2.0

3.5

or

90%

12

dia

5

dia

83%

Piles

Foundation

SP

4C

0.0

2.0

2.5

or

85%

12

dia

7

dia

66%

Land & Fresh water

SP

4C

0.0

3.0

3.0

or

90%

12

dia

6

dia

75%

Zone 1

Zone 2

Marine

Sawn

SP

5A, B & C

0.0

0.5

0.5

2.0

3.5

or

90%

6

8

3.5

5.5

60%

Round

SP

5A, B & C

0.0

0.5

0.5

2.0

3.5

or

90%

12

dia

8

dia

56%