The HEPA filter could be damaged and the balance of airflow could be disrupted. DON'T leave the view screen open when the cabinet is not in use. Keeping the screen closed between uses will help keep any contaminants in the room from getting inside the cabinet. DON'T eat, drink, chew gum, store food, or smoke near the cabinet. If the cabinet is accidentally contaminated, you may ingest toxins.
Sudden movements can disrupt the airflow and compromise safety.
ALL biosafety cabinets need to be recertified annually. Scientific Inc. has produced a very helpful article on the subject .