There are several sources of information in the Industry at the moment reagarding gate safety. The most relevant and official document currently available is from the Powered Gate Group of the DHF (Door Hardware Federation). link here
http://www.dhfpoweredgategroup.co.ukThis document was produced by members of the group and was commented upon by the HSE (Health & Safety Executive) who approved the advice given within. Within this guide it is pointed out that almost all gates (except those exceptional circimstances where no untrained user can get anywhere near the gate) would need to be assessed for risk and protected with force limitation (and or) pressure sensitive equipment (safety edges). In fact HSE's own documentation points out that it does not consider inherrent force limitation in drives alone to be sufficient to protect a gate. link here
http://www.hse.gov.uk/safetybulletins/electricgates.htm CAT2 & CAT3 are also explained in more detail in the DHF guide, however to quickly summarise CAT2 can only be used if "TESTED" by the control panel of the gate control board. This "TEST" requires a special output from the automation panel to complete before each movement of the gate. For scenarios where the control panel does not have this test feature CAT3 must be used.