Forestry Commission Scotland logo
Oversize chip and tape measure

Quality standards for wood chip

Standards for wood chip fuel are used to describe the particle size characteristics and the moisture content of the chips, but they can also describe variables such as ash content, limits for contamination, calorific value and bulk density.

The official quality standard is BS EN ISO 17225-1.

Under this standard, particle size distribution is described with the 'P' prefix (P16b, P45 etc) and moisture content with the 'M' Prefix (M25, M30 etc).

Note that there is no difference in the standards for naturally or mechanically dried wood chip, it will just be easier for producers of mechanically dried chip to produce lower moisture chip and to ensure a consistent moisture content, as the finished product does not rely upon natural seasoning and the variability of weather and climate.

Particle Sizes

 

Main Fraction (min 75% by weight)

Fines Fraction (% by weight smaller than 3.15 mm)

Coarse Fraction (% by weight)

Max particle length/ Max cross sectional area

P16A

3.15 mm - 16 mm

Less than 12%

Less than 3% over 16 mm

31.5 mm / 1.0 cm2

P16B

3.15 - 16 mm

<12

<3% over 45 mm

120 mm / 1.0 cm2

P45A

8 - 45 mm

<8

<6% over 63 mm

120 mm / 5.0 cm2

P45B

8 - 45 mm

<8

<6% over 63 mm

350 mm / 5.0 cm2

P63

8 - 63 mm

<6

<6% over 100 mm

350 mm / 10.0 cm2

P100

16 - 100 mm

<4

<6% over 200 mm

350 mm / 18.0 cm2

The sizes given relate to the sieve hole diameter.

Moisture Content

Moisture content - wet basis i.e.  mass of water as a percentage of the wet weight

M15

Less than or equal to10%

M20

<=20%

M25

<=25%

Then in 5% increments up to 55%

Ash

Ash content, weight as a percentage of the dry weight

A0.5

Less than or equal to 0.5%

A0.7

<=0.7

A1.0

<=1.0

A1.5

<=1.5

A2.0

<=2.0

A3.0

<=3.0

A5.0

<=5.0

A7.0

<=7.0

A10.0

<=10.0

A10.0+

Over 10%

 

The full quality standards for wood chips can be purchased from the BSI website.