FDA specifies these measurements for 4 of the zones.
Zone 1: Within the Rail
Zone 2: Under the Rail, Between the Rail Supports or Next to a Single Rail Support
Zone 3: Between the Rail and the Mattress
Zone 4: Under the Rail, at the Ends of the Rail
Zone 5: Between Split Bed Rails
Zone 6: Between the End of the Rail and the Side Edge of the Head or Foot Board
Zone 7: Between the Head or Foot Board and the Mattress End
Note: The above picture and exact verbiage appears on page 13 of "Hospital Bed System Dimensional and Assessment Guidance to Reduce Entrapment" at www.fda.gov/downloads/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/ucm072729.pdf. On page 21, the FDA lists recommended dimensional limits for zone 1 through 4 (the zones involved in the majority of the entrapments reported to the FDA). These are as follows:
Zone 1: Within the rail
<120 mm (< 4 3/4 inches)
Zone 2: Under the rail, between rail supports or next to a single rail support
< 120 mm (< 4 3/4 inches)
Zone 3: Between rail and mattress
<120 mm (< 4 3/4 inches)
Zone 4: Under the rail, at the ends of the rail
<60 mm (< 2 3/8 inches) AND >60° angle
Additional resource: For a helpful set of FAQs related to bedrail safety, go to http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/GeneralHospitalDevicesandSupplies/HospitalBeds/ucm123467.htm.