AAMI standards require a surgical gown to pass ASTM International F1671 in the critical zones in order to be labeled an AAMI level 4 surgical gown. What areas are included in the critical zone? There are typically four different areas that must pass within the critical zones, including two in the front chest and two on the sleeves. If a product passes ASTM InternationalF1671 in all applicable areas, then it qualifies as an AAMI level 4 surgical gown.