The present invention provides a chamber having at least one operator hand access port the port comprising a port aperture located within the chamber wall and at least two flexible non-resilient lightweight sealing gas-tight flaps (SFs), disposed the same plane of the port aperture in an overlapping manner, entirely enclosing the port aperture each of the SFs is defined by a port aperture edge and chamber edges the chamber edges are anchored to the chamber wall along more than half of the perimeter of the flap, at a distance from the center of the port greater than the radius of the port and beyond its perimeter the port aperture edge of each flap is stretched across an entire chord of the port aperture stretched port apertures edges define an interior access zone, disposed the same plane of the port aperture, characterized solely by the port aperture edges.
