It's important that you understand that back belts should not be considered personal protective equipment in that they physically "protect" you from back injuries.

Back belts are not recognized by OSHA as effective engineering controls to prevent back injury. While they may be accepted by individual workers because they feel as if they provide additional support, the effectiveness of  back belts in the prevention of low back injuries has not been proven in the work environment.

Thus, OSHA does not forbid the use of back belts and similar devices, nor does it endorse their use.