Memorandum - NHTSA

V-29
Platform Free-Fall Velocity Limits (S6.6) - During the operation of the lift, a loss of hydraulic
pressure/electrical power or a mechanical failure could occur, with the lift at the bus floor level
[1,013 - 1,267 mm (40-50 in.) off the ground], in which case the person on the lift may be subjcct
to a free-fall condition. A free-fall from 1,267 mm (50 in.) results in an impact velocity of 5 m,’s
(1 1 mph). The Final Rule requires a maximum free-fall velocity or terminal velocity of 305
“/s (12 inhec.). Compliance with this requirement is made through engineering analysis
assuming a 272 kg mass (600 lbs.) load. In case of a single point failure, the lift platform cannc )t
change angular orientation more than 2 degrees in any direction. This test applies to both
primary power source and manual backup operating modes. The free-fall speed is about twice
the normal lift operating velocity of 152 m ds (6 in./sec.). In the event of a power or mechankal
failure this speed is safe enough to ensure that impact injuries do not occur. The free-fall
velocity limit and no excessive change in platform angle are consistent with the Access Board
that prohibits the platform from accelerating to the ground, with a user on-board, due to a sing1e
point failure. It is believed that all lift equipment currently on the market will comply. There
will be no incremental cost impact.
Control Systems (S6.7) - The FTA-sponsored guidelines indicate that lift operator error
contributes to a significant proportion of lift accidents and can also cause maintenance and
reliability problems. The requirements for control sequences and standardization is designed 10
reduce the potential for human error. Several factors have been identified which contribute to
operator error: (1) the lack of familiarity with the lift controls, (2) the lack of standardization i 11
the control sequence and types of controls (e.g., different controls for different lifts); and (3) the