A mobile environmental containment unit has an upper frame with a sealing surface, a flexible, transparent impermeable envelope with an open top and one or more access openings that depends from the upper frame, and a lower frame that is supported by the envelope. The upper frame of the unit is supported by telescoping support members with the sealing surface of the upper frame and the open top of the envelope fitted against a portion of a ceiling which is accessible by a workman via the one or more access openings and the open top of the envelope.