Portable ventilating apparatus for purging underground installations and the like

For use in combination with a rimmed vertical entryway into a space to be ventilated, the assembly which comprises:

• an endless collar having upper and lower open ends and a wall shaped to fit within the entryway and leave an annular gap therebetween for the passage of exhaust air, gap-bridging means depending from the collar operative to support the latter within the rimmed entryway without appreciably obstructing the flow therebetween, a tapered nozzle centered within the collar so as to leave a space therebetween, a forced air blower connected to the nozzle operative to direct a stream of air downwardly therethrough, a duct hanging from the underside of the collar forming an elongate continuation thereof, and an upwardly and outwardly flared deflector bordering the upper open end of the collar, said nozzle and collar cooperating with one another and with the blower when the latter is operative to aspirate air into the duct over the top of the deflector, and said deflector being effective to turn the air exhausted through the annular gap aside so no significant quantity thereof will be reaspirated into the duct.