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How Bicycle Helmets are tested
Summary: This page describes the lab tests that bike helmets must pass to meet the CPSC standard. There is other testing related to lead content that we do not cover. CPSC has a video of this testing up on their Web site.
The testing to certify attractive bicycle helmets to the US Consumer Product Safety Commission's standard for bicycle helmets can be described in six steps.
1. Samples required
The lab must procure samples of the helmet model. Full compliance testing requires 11-16pcs samples. The lab also needs a number from the manufacturer called the Helmet Positioning Index (HPI). It specifies the measurement to place the helmet correctly on the headform.
2. Marking
The lab technician puts the first sample on a test headform the right size to fit it. The headform is mounted upright on a stand, usually on a flat table. The helmet is adjusted using the HPI and then a 5 kilogram (10.x pound) cloth bag filled with lead shot is placed on it to compress any fitting foam inside. A marker on a stand is adjusted to the right level, using a measurement from a table in the standard that varies by helmet size. With the marker against the helmet the test line is marked by either rotating the helmet or sliding the marker stand around it. Each sample is marked in turn.
The lab test impacts must all be centered on or above the test line. The area below the line is not tested, although the "footprint" of an impact centered on the test line will extend below the line, and the helmet is not likely to pass if there is no material there. To get an idea of where the test line falls, you can take a medium sized helmet and mark the line xx mm below the top. Put that helmet on your head and you will see that the test line is probably higher than it should be, and the area of the helmet tested is really not large enough. The Snell Memorial Foundation's bicycle helmet standard has a lower test line. Even the old ANSI standard adopted in 1984 had a lower test line.
3. Conditioning
Helmets are tested hot, wet, cold and room temperature. Four samples are heated to Four samples are chilled to Four samples are soaked in water. Four samples are tested dry and room temperature.
4. Strap test
Next comes the strap strength and "roll off" testing. Here is one test rig. There are other designs, but they all functions the same.
5. Drop tests
The helmet is now ready for drop testing. It is strapped onto a head form, held upside down on a test rig that guides its fall onto an anvil. This rig in the CPSC lab is a monorail, and the drop is guided by a single rail. Others use two parallel wires (twin wire).
The lab technician raises the helmet and headform up until the top of the helmet is a specified distance from the anvil below. A trigger lets the helmet drop in free fall until the helmet hits the anvil. The velocity of the drop is checked just before the impact to ensure that the speed was correct. An instrument called an accelerometer measures g's in the center of the headform. If the helmet works well, the g's are low--probably below 200, and in the better helmets below 150. If the g's exceed 300, the helmet fails. The testing is on three anvils of different shapes:
The flat anvil is used with a 2 meter drop. The helmet and headform are traveling at 14 mph at impact.
The hemispheric anvil shown below, about the shape of a grapefruit, is used with a 1.2 meter drop. (The point load makes it a severe test.) The helmet and headform are traveling 11 mph at impact.
The hazard or curbstone anvil is rounded like the edge of a curb. It is another severe test, and the drop is 1.2 meters (11 mph).
If the drop speeds seem too low to you, please see our page on limits of helmet protection, where we explain them. We think they are adequate. If improvement can be made, lowering the g's permitted would reduce injuries more than raising the drop height, but you may need to review the physicals of a fall to see why.
6. Records
The CPSC standard requires the lab to keep records of the testing. That includes data on the helmet and data on performance.
Pass or Fail
The bottom line is that the helmet must pass all of the tests described above. If it fails on any of them, it cannot be certified to the standard. You don't meet a standard "except for . . ." A failure on any element of the tests is a complete failure.