2. Attach the block of wood to the wall at the height of the operator/wearers head
above the shoulder blades when the operator/wearer is standing.
3. Have the operator/wearer stand with back of head against block. Ensure
posture and body alignment are as straight as possible. The operator/wearer
should hold his or her head in a comfortable position while focusing on a point
directly ahead at eye level.
4. Referring to Figure 4-6, view (A), use a ruler (Item 21, Appendix B) to measure a
distance 1-1/2 above operator/wearers pupil. Using a marker, make a small
mark at this point in the center of the operator/wearers forehead; this is known
as the forehead reference point.
5. Referring to Figure 4-6, view (B), use a combination square (Item 5, Appendix B)
to measure from the forehead reference point to the block; this is the head
length. Be careful to just touch the operator/wearers skin at the forehead
reference point. Ensure that the square is parallel to the floor and centered on
6. Select the correct helmet size based upon head length as follows:
MAXIMUM HEAD LFNGTH
8-1/16 - 8-5/16
7-3/4 - 8
7-7/16 - 7-11/16
7-1/8 - 7-3/8
Figure 4-6. Determining Head Length for Helmet Sizing