Here are some of current seat belt standards, that are available to you through BSOL:
BS ISO 13216-3:2006
Road vehicles. Anchorages in vehicles and attachments to anchorages for child restraint systems. Classification of child restraint dimensions and space in vehicle.
BS ISO 6487:2015
Road vehicles. Measurement techniques in impact tests. Instrumentation.
PD ISO/TS 17242:2014
Quasi-static calibration procedure for belt force transducers.
BS ISO 13218:1998
Road vehicles. Child restraint systems. Report form for accidents involving child passengers.