Settle plate

A 90 mm agar plate left open to collect micro-organisms falling from the air by gravity, for up to 4 hours. Settle plates are used in Grade A and B throughout critical operations because they give continuous coverage. Results are in CFU per 4 hours: no growth in Grade A and 5 CFU in Grade B under Annex 1. The site must show that the agar does not dry out and lose recovery over the exposure time used.