9 pressurization and purge control systems, namely, control units, filters, relief valves, outlet orifices, and spark arrestors, sold individually and as a unit; pressurized, dust-tight, flame proof and explosion proof electrical enclosures; and, intrinsically safe information technology products, namely, equipment used with computers and multi-media applications, specifically, keyboards, trackballs, joysticks, computer monitors, bar code readers and components thereof which have been designed and manufactured to be used safely in the presence of explosive gas or dust