Stainless steel flame retardant filters are mainly used in the culinary industry (in particular, above appliances in kitchens), and come in types A and B.
Differences between type A and type B:
Section 8.2 of DIN 18869-2 states that type A filters must be flame retardant. These filters must be used in food kiosks, cook and chill areas, or while cooking in a guestroom, for example.
If a filter allows flames to penetrate during testing or does not undergo any testing whatsoever, then it is considered a type B filter. These filters can be used (for example) in areas where food is served or stored or in dishwashing areas.