OSHA standards for delivery drivers.?

My husband is a delivery driver for a company I'll leave the name omitted. Several of the delivery drivers have heard and suspected that the first step into the truck is higher than what OSHA standards allow. Many of the guys, including my husband, have muscular skeletal disorders, especially in their back and hips that could potentially be caused by this. I was wondering if someone knew or knew where I could find the measurement standards that OSHA requires for the first step from the ground into the truck.