Flammable solvent units are designed using the guidelines
allowed in NFPA 69, Standard on Explosion Prevention Systems.
Since these system require high concentrations of combustible
solvents to perform the cleaning process, the main deflagration
prevention method used is by oxidant concentration reduction.
Within these systems the three major tanks containing solvent
are all enclosed and are all operated under vacuum to ensure
that these tanks are sealed and completely isolated from the
ambient surroundings during operation, idling and shutdown.
This type of system is allowed under Section 5.1 that states:
5.1 Application. The technique for oxidant concentration
reduction for deflagration prevention shall be permitted
to be considered where a mixture of oxidant and flammable
material is confined to an enclosure within which the oxidant
concentration can be controlled.
Vacuum to Vacuum systems are ideal for the control of oxygen
within the whole processing system. The main vessel is evacuated
before any introduction of solvents. All other tanks operate
under pure vapor and are monitored for increased pressure
due to leakage in. Solvent cannot leak out while under vacuum.
Systems using Acetone for plastic leaching, Cyclohexane for
difficult flux removal and Isopropyl alcohol for medical devices
are in the field. Combining Vacuum to Vacuum systems with
the VCN process is an easy modification and has worked very
effectively in the field. Any flammable solvent can be used.