Abstract: An expandable barrier for isolating a mine entry or similar open area is disclosed wherein the expandable barrier includes an expandable hollow curtain or bag housed within a horizontal brace member connected to the roof of an entry, the expandable hollow curtain being connected to vertical brace members adjacent to the walls of the mine entry. The expandable bag fills with a material capable of expanding the bag, such as a foam-like material, and expansion of the bag causes the bag to descend downwardly from the first horizontal brace member. The bag fills with distensible material in response to a stimulus detected by a monitor associated with the containers which contain the distensible material. A closeable opening or flap is disposed in the bag to allow passage of people or equipment therethrough. The expandable barrier may also be oriented in a horizontal position for use in vertical shafts.