CEAC-2020-10-October

News
Reconsidering Composite Vents for
Explosion Protection
Wherever combustible dusts can accumulate, the risk of
an explosive event is present. This poses a significant risk
to industries such as Food, Grain, and Feed. In response to
this hazard, in 1945 the National Fire Protection Association
(NFPA) initiated a tentative standard, NFPA 68, titled ‘Standard
on Explosion Protection by Deflagration Venting.’ Updated
in 2007 to a Standard, it is currently in its 2018 revision
that provides specific direction to mitigate the risk through
the use of venting. Today, explosion venting is the most
commonly used method of mitigating the pressure effects of
a deflagration.
Designed to open rapidly at a predetermined burst pressure,
explosion vents allow the combustion process to escape to
the atmosphere, while limiting the pressure generated inside
the process equipment to calculated safe limits.
This type of vent is installed on dust collections, conveyors,
bucket elevators, dryers/ovens, bins, and silos.
For more than 50 years, traditional composite vents comprised
of plastic film sandwiched between two stainless steel
sheets have been utilized for this purpose. However, this design
approach has largely fallen out of favor in all but a few
niche applications due to significant disadvantages, including
the risk that dust and process debris can accumulate such
that it affects the speed and reliability of the vent opening.
“Over time there can be an evolving risk with composite
vents that leakage will occur, or that dust or process materials
will accumulate within the layers and the vent will become
very heavy and won’t function as it should,” says Geof
Brazier, president of BS&B Pressure Safety Management, a
manufacturer of a broad range of dust explosion prevention
and protection technologies.
This has some facility personnel taking a closer look at
The center-opening traditional composite vent in mounting frame is shown
here.
more advanced single sheet vent alternatives that weigh less
and include design features that make them more durable,
even in the presence of light vacuum conditions or vibration.
These modern options also reduce installation costs while
increasing service longevity.
Vent Inspection
NFPA 68-2018 Standard on Explosion Protection by Deflagration
Venting establishes requirements for the design,
location, installation, maintenance, and use of devices and
systems that vent the combustion gases and pressures resulting
from a deflagration within an enclosure so that structural
and mechanical damage is minimized.
Within the NFPA 68 Standard is the requirement that
installed explosion vents in service “shall be inspected” to ensure
their integrity as they perform a critical safety function.
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| Chief Engineer