SAE AS4059: The American standard for fuel cleanliness

SAE AS4059 is the standard that regulates fuel cleanliness in the US and Canada. It is the latest revision of the now defunct NAS 1638 code, which was developed in 1964 to define classes of particulate contamination in aircraft components and hydraulic fluids, but has been invalid since 2001 and has since been replaced by SAE AS4059.

The SAE AS4059 standard is a code set by the Society of Automotive Engineers (SAE International) to measure the solid particulate content of fuel samples and hydraulic fluid.

SAE International is a U.S.-based, globally active professional association and standards developing organisation for engineering professionals in various industries.

The below table shows how solid particulate contamination in fuel can be classified according to the SAE AS4059 code. The figures refer to the solid particle count per millilitre of stored fuel.

	Maximum contamination limits (particles per ml)
Size code	A	B	C	D	E	F
000	195	76	14	3	1	0
00	390	152	27	5	1	0
0	780	304	54	10	2	0
1	1,560	609	109	20	4	1
2	3,120	1,220	217	39	7	1
3	6,250	2,430	432	76	13	2
4*	12,500	4,860	864	152	26	4
5	25,000	9,730	1,730	306	53	8
6	50,000	19,500	3,460	612	106	18
7	100,000	38,900	6,920	1,220	212	32
8	200,000	77,900	13,900	2,450	424	64
9	400,000	156,000	27,700	4,900	848	128
10	800,000	311,000	55,400	9,800	1,700	256
11	160,000	623,000	111,000	19,600	3,390	512
12	320,000	1,250,000	222,000	39,200	6,780	1,024

*This is the exact equivalent to the ISO code 18/16/13, which is the particulate cleanliness level required in Europe for fuel to be recognised as ‘clean’.