This July 20, 2007, M2010 draft standard incorporates the best advice from the helmet community received to date

Draft M2010 Cover 7/31/2007 EBB

This July 20, 2007, M2010 draft standard incorporates the best advice from the helmet community received to date. There are several changes to consider:

Lower Impact Test Criteria: The peak G limits have been changed to current European requirements or, when more conservative, to values implicit in M2005 test procedures.
Reduced Impact Test Severities: Some of the figures for second impact velocities were considered impractical.
Change to the Retention Strength Test: Whenever practicable, helmets will be supported by the shell edge for this test.
More samples required: Seven samples instead of five may be necessary to test some models in certification.

Impact Test Criteria

The directors have reduced the peak G limits generally to encourage compatibility with European requirements but they have further reduced the limits for the largest helmet sizes to ensure that M2010 will demand shock attenuation comparable to current and previous Snell standards.

The reasoning for the peak acceleration considerations is as follows: the increased mass of the larger head forms would permit helmets with much denser liners to meet current peak acceleration limits. In order to ensure that the largest helmets will transmit shocks no greater than those currently allowed, the peak G criteria for the two largest head forms, the M and the O, have been reduced to 264 G and 243 G respectively. These limits are well below the 275 G and 400 G limits called out by the European Standard, ECE 22-05, and by the United States DOT standard, FMVSS 218. However, Snell standards, by their structure, have always demanded more shock attenuation for larger heads. Effectively, this draft sets a peak G criterion of 275 G for the A, C, E and J head forms but sets a peak force criterion of 14500 newtons for the M and O head forms.

Impact Test Severity

The changes to the test severities are based on the limits of current helmet technology. Since the first draft of the M2010 standard went out, knowledgeable individuals and manufacturers have come forward with practical advice regarding those aspects of the draft that were unobtainable or unreasonable. The directors welcome this sort of advice and, if the arguments are cogent and the recommendations will not confer an unfair advantage upon any particular company, the directors will make the necessary corrections to Snell standards.

Previously, Snell standards had set the same requirements for helmets regardless of size. Since the masses of the test head forms were all the same, manufacturers could often accommodate different sizes by scaling the same design up or down with only slight changes, if any, in liner density and other material properties. However, the introduction of different head form masses imposes significantly higher levels of shell stress on the largest helmets during testing. The peak force criterion set for the largest head forms addresses this problem to a degree but now the largest helmets must use more liner thickness to manage an impact of a given velocity. Rather than force the industry to thicker liners and bulkier helmets, the test impact velocities for the largest helmets have been adjusted to demand protective capabilities comparable to current M2005 certified headgear.

There is a different problem for the smallest helmet sizes. The lighter head forms impose much lower levels of stress so that there may be little or no shell damage particularly in impacts with flat surfaces which do not concentrate the shell loading. Currently, the loadings in flat anvil impact build as the head form crushes into the liner bringing more and more of its surface into contact with it. The peak forces and accelerations only start to level out at the point that the shell itself reaches its stress limits and begins to fail. However, with much lighter test head forms, the shell does not appear to reach these limits. Instead, the head form accelerations may increase beyond the test criterion toward the end of the test but well before the crush limit of the liner is reached. Since the hemispherical anvil applies a concentrated shell load, the shell begins to break apart during the impact attenuating the forces applied to the head form and preventing the head form acceleration from increasing beyond the test criterion at least until the crush limit of the liner is reached. This phenomenon leads to the paradoxical situation of a helmet being able to manage greater impacts against the hemispherical anvil than against the flat. The draft M2010 addresses this problem by limiting the second flat anvil impacts against the flat anvil to 7.09 m/sec. As a result, the impact velocities called out in this draft depend on test type, anvil and head form size and the peak G criterion depends on test type and head form size.

The M2010 impact test requirements, summarized in the following table, are substantially more complicated than in previous Snell standards. But there are some advantages: the technologies demanded for the largest helmets are more similar to those used in helmets currently certified to M2005. Manufacturers of helmets suitable for testing on the M or O head forms may find only slight modifications are necessary to reconfigure these items for M2010. Current M2005 certified helmets for the A, E or J head forms will require more extensive changes, particularly to the liner densities but I hope the changes proposed in the new draft will simplify the problems somewhat and enable much of the current M2005 technology to carry forward into M2010.

M2010 Impact Testing
Head Form				A	C	E	J	M	O
Test Criteria		Certification		275 G	275 G	275 G	275 G	264 G	243 G
Test Criteria		RST		285 G	285 G	285 G	285 G	273 G	251 G
Certification Velocities	Flat & Edge		1st	7.75 m/s	7.75 m/s	7.75 m/s	7.75 m/s	7.75 m/s	7.75 m/s
	Flat & Edge		2nd	7.09 m/s	7.09 m/s	7.09 m/s	6.78 m/s	5.73 m/s	5.02 m/s
	Hemi		1st	7.75 m/s	7.75 m/s	7.75 m/s	7.75 m/s	7.75 m/s	7.75 m/s
	Hemi		2nd	7.75 m/s	7.38 m/s	7.09 m/s	6.78 m/s	5.73 m/s	5.02 m/s
Deviation Velocities	Flat & Edge		1st	7.48 m/s	7.48 m/s	7.48 m/s	7.48 m/s	7.48 m/s	7.48 m/s
	Flat & Edge		2nd	6.85 m/s	6.85 m/s	6.85 m/s	6.55 m/s	5.54 m/s	4.84 m/s
	Hemi		1st	7.48 m/s	7.48 m/s	7.48 m/s	7.48 m/s	7.48 m/s	7.48 m/s
	Hemi		2nd	7.48 m/s	7.13 m/s	6.85 m/s	6.55 m/s	5.54 m/s	4.84 m/s

Retention Strength Testing

The remaining technical change to the standard involves the retention strength test. The softer liners demanded, particularly for the smaller helmets suggest that the maximum deflections measured for the dynamic loading of the chinstrap may be increased by a few millimeters due to compression of the liner against the top of the supporting head form. For this reason, the draft proposes to support the test helmets on their lower shell edge. Since this may not be practical for some helmet configurations, the test technician, at his discretion, may opt to support the helmet on a head form. If the helmet meets the test requirements in either of these support configurations, it shall be deemed to meet the standard.

Number of Test Samples Required

The additional complexities of this standard, particularly in the impact testing have also prompted an increase in the number of test samples. In previous Snell standards, if a helmet met impact requirements on the largest appropriate head form, it would also meet them reliably on smaller test head forms. However, for M2010, helmets must be tested on the largest and smallest appropriate head forms if there is to be any confidence that helmets will meet requirements reliably throughout their intended size ranges. If the helmet is sized so that only a single head form is appropriate for testing, M2010, like M2005, requires five samples fitted for the largest intended head size. But if the helmet’s intended size range implies that two or more head forms are appropriate, M2010 demands two additional samples fitted for the smallest appropriate size.

Test Head Forms as Determined by Size Specification
		Largest Size Specified
		50 - 51	52 - 53	54 - 56	57 - 59	60 - 61	>61
Smallest Size Specified	<52	A	A-C	A-E	A-J	A-M	A-O
	52-53		C	C-E	C-J	C-M	C-O
	54-56			E	E-J	E-M	E-O
	57-59				J	J-M	J-O
	60-61					M	M-O
	>61						O

The table shows the head forms considered appropriate to head size ranges given in terms of centimeters of circumference. If a helmet’s specified size range falls into one of the light gray cells along the table’s principal diagonal, only a single head form is deemed appropriate and only five samples fitted to the largest intended size are necessary. Otherwise, the two or more head forms are indicated and the manufacturer must provide two additional samples fitted to the smallest intended head size.

It is my devout hope that the Foundation’s M2010 program will consist of helmets which will satisfy all mandatory requirements set in North America, Europe and throughout the world and which will incorporate protective capabilities well beyond all those mandatory requirements.