36 CFR Part 1195 Standards for Accessible Medical Diagnostic Equipment - Preamble

b. Exception for Base Support Allowance and Unobstructed Knee and Toe Space

In the proposed rule, obstructions were not permitted within the knee and toe clearance space. This is consistent with the requirement in the existing accessibility guidelines and standards. One manufacturer commented on this provision, asserting that mammography equipment poses unique challenges and requires separate consideration. The commenter explained that the gantry of a mammography machine includes a base lip which is required for structural and seismic stability, and protrudes into the knee and toe clearance. This commenter recommended revisions to allow for a base lip on mammography equipment.

The MDE Advisory Committee recommended allowing obstructions into the knee and toe clear space, up to a height and depth that still permits the footrests of wheelchairs to pass over it. Specifically, the Committee recommended allowing base supports to be a maximum of 1½ inches high and allowing an additional sloped region above the base support at a depth of 25 inches from the front edge of the breast platform at 1½ inches above the floor, which can extend to a height of 4 inches above the floor at a depth of 28 inches. The MDE Advisory Committee explained its recommendation, noting that:

• The base support is of fundamental importance to mammography equipment and provides structural support, seismic stability, and installation safety. It does obstruct the floor space in front of the gantry and, thus, may limit how close a wheelchair can get to the equipment. To respond to this issue, industry proposed a configuration that would cause minimal obstruction to the floor space in front of the gantry and would allow footrests to ride over it.

To discuss the maximum base support height, the sub-committee looked at anthropomorphic data regarding footrest heights. The footrest height data measures the height from the floor to the top surface of the footrest at its proximal outside corner. To determine the necessary clearance for the footrests, the Committee used the footrest height data and subtracted the thickness of the footrests (~0.5 inch). Allowing a maximum base support height of 1.5 inches will provide room for the structural components necessary for an effective base support design and will also be accessible by around 92% of manual chair users and over 95% of power chair users. MDE Advisory Committee Report, 123-127, available at https://www.access-board.gov/guidelines-and-standards/health-care/about-this-rulemaking/advisory-committee-final-report.

The Access Board concurs with the need for permitting base components in the knee and toe clear space for mammography equipment. While the Access Board recognizes that this is a deviation from existing accessibility guidelines and standards, the Board believes that mammography equipment presents special challenges due to the diagnostic, structural, and seismic requirements of the diagnostic equipment. In the final rule, the Access Board has created an exception to the height requirement for breast platforms. This exception permits the profile of base components to extend into the wheelchair space at a height of 1½ inches maximum between 17 inches minimum and 25 inches maximum in depth measured from the leading edge of the breast platform. In addition, the Access Board has found that the profile of the base components should increase toward the rear of the clearance space where a patient’s foot and toes will be higher than the heel supporting portion of the footrest. Therefore, the final rule requires that from 25 inches to 28 inches measured from the leading edge of the breast platform, the height of the component above 1½ inches must be beveled at a rate of 2.5:3. This exception preserves a 17-inch minimum of unobstructed floor space measured from the leading edge of the breast platform.