Fume cupboard capture and containment control

Perhaps the most important health and safety control measure in wet chemistry laboratories is the fume cupboard. Opening and closing a sash by an operator will normally cause a major disturbance on airflow systems that requires a fast response to maintain stability and precision.

Speed of response

As an operator moves the fume cupboard sash, the control system needs to respond by reaching stable airflow control within 1 to 3 seconds. A slower speed of response more typically found in a traditional single fan control system may create a hazard for personnel. To demonstrate this further the following video tests different speeds typically found in the field.

Dynamic testing of a fume cupboard at the factory. Video courtesy of Phoenix Controls

Dynamic containment testing is prescribed in ANSI Z9.5 and ASHRAE Standard 110. Australia’s standard AS 2243 Part 8 has a similar requirement.

Pressure independent control sequence

Rather than enforcing a factory like aesthetic look to the roof with many dedicated exhaust stacks and fans, owners can instead operate an energy efficient manifolded exhaust system with a roof plenum, redundant fans and stack assembly.

However, with manifolding exhausts a new variable is introduced to control – a pesky instability caused by rapid changes in ductwork static pressure due to lowering and raising fume cupboard sashes throughout the facility. While the engineer might consider oversizing ductwork to reduce static pressure, this is rarely possible due to spatial and budget restrictions. Instead, we recommend greater control by designing in venturi valves at each fume cupboard with an integral mechanical pressure independent assembly to deliver instant response to pressure changes.

When both speed of response and stability of airflow are under control the manifold laboratory exhaust system will be safe and efficient.