Local exhaust ventilation principles

Many industrial local exhaust ventilation systems have inadequate performance. This occurs because systems were poorly designed. Frequently, the performance of the local exhaust ventilation systems is impaired because of modifications. Nine factors which should be considered when designing a local exhaust ventilation system include: 1. minimizing capture distance; 2. providing adequate capture velocity (or adequate exhaust rate); 3. using gravitational force; 4. providing adequate conveying velocity for particulates; 5. minimizing pressure drop; 6. incorporating "containment" whenever possible; 7. providing even airflow distribution at hood faces; 8. placing the fan as the last system element whenever possible; and 9. installing a static pressure gauge and testing the system.