(a) the laboratory fume hood is connected to a local exhaust ventilation system;

(b) the average face velocity across the operational face opening of the laboratory fume hood is 0.4 m/s to 0.6 m/s;

(c) the face velocity is not less than 80% of the average face velocity required under paragraph (b) at any point across the operational face opening of the laboratory fume hood; and

(d) the face velocity is not more than 120% of the average face velocity required under paragraph (b) at any point across the operational face opening of the laboratory fume hood.