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All glove boxes should preferably be equipped with a mechanical
pressure relief device to cater for an abnormal failure occurrence.
An abnormal failure occurrence can take place when any device or
equipment which may create an under or over pressure situation in
a containment vessel, cannot be maintained by, and within, the system
design.
Without a mechanical pressure relief device, any abnormality within
the system beyond design limitation risks either an explosion or
an implosion of the glove box containment. Abnormalities can take
place such as gas purge valves sticking in the open position, in
glove box equipment failure releasing gas or liquids, inner antechamber
door left open during an evacuation routine.
Whilst rigid glove boxes are normally designed to take pressure
in excess of the bursting pressure of a glove box glove, such an
occurrence would render the glove box fully open to the air environment.
Additionally negative bursting of gloves can have serious consequences
on fragile equipment within a glove box, particularly if glass containers
are fractured containing pyrophoric material.
Pressure relief bubblers consist of a "U" bend of liquid,
which as the title suggests, will release any over or under pressure
beyond the backpressure created by the depth of liquid. Bubblers
are available in positive only versions or dual pressure to cater
for either positive or negative overpressure.
Positive only pressure relief bubblers are at risk of depositing
their liquid contents into the glove box should they be subject
to a negative overpressure situation. Dual pressure relief bubblers
will provide for the release of any over or under pressure beyond
the liquid set depth, whilst maintaining a seal.
For anaerobic and dry glove boxes, any negative overpressure that
causes the bubbler to operate will mean the loss of that environment,
and for this reason positive pressure relief bubblers are often
specified in favour of the more expensive dual models.
(Normally only provided as part specification of a glove box system
supply.)
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