The supercritical air mobility pack (SCAMP) is a prototype self-contained breathing apparatus designed for use in rescue and fire-fighting operations (see figure). The SCAMP is based on the storage of air at supercritical pressure in a temperature range slightly above that of liquid air. Like breathing apparatuses based on the storage of liquid air ("liquid-air packs," for short), the SCAMP offers the advantages of compactness and light weight. In addition, the SCAMP offers the following advantages, as explained below:

In the SCAMP, air is stored essentially as a supercold compressed gas by maintaining its pressure above the critical level of 560 psia (3.86 MPa absolute). In the supercritical condition, the stored air behaves as a single-phase fluid, with no differential boiling or other separation of constituents and thus no change in chemical composition during storage. Because of the feature, the SCAMP is not susceptible to oxygen enrichment. Thus, air may be added to the vessel after storage, rather than emptying and refilling the vessel as required by current liquid-air pack technology. Moreover, there are no separate liquid and vapor volumes in the single-phase fluid; instead, the single-phase expands to occupy the entire volume of the storage vessel, making it possible to position the open end of the supply tube anywhere in the vessel to withdraw the fluid in any orientation.

SCAMP Self-Contained Unit uses a heat exchanger to warm the expelled air to make it breathable. The apparatus is designed for rescue and fire-fighting operations.

The storage vessel of the SCAMP is a Dewar tank that is filled with supercritical cold air, then mounted inside a molded plastic backpack. A heat exchanger in the backpack provides for a limited flow of heat from the surroundings into the vessel to expel air for breathing. Another heat exchanger in the backpack warms the expelled air to ambient temperature to make it breathable. The heat exchangers operate in conjunction with a pressure-actuated bypass valve; together, the heat exchangers and valve maintain the stored air at a pressure of 750 psia (5.17 MPa absolute) during expulsion at ambient temperatures from -40 to 120 °F ( -40 to 49 °C), at flow rates from 10 to 150 standard liters per minute.

A standard self-contained-breathing-apparatus pressure regulator and face mask are used to control and deliver the flow of breathable air to the wearer. A light-emitting-diode device on the backpack harness indicates the amount of stored air remaining in the vessel and an audible alarm is generated when less than 25 percent of the nominal full amount remains. The nearly empty vessel can be rapidly removed from the backpack and replaced with a full one.

The development of the SCAMP was accompanied by the development of an automatic loading system that reduces the difficulty of filling the storage vessel. About the size of a household refrigerator, the system requires a Dewar flask of liquid nitrogen plus electrical power of less than 100 W for operation. The system takes about 5 minutes to load a vessel rated for 1 hour.

This work was done by Harold L. Gier and Richard L. Jetley of Aerospace Design & Development, Inc., for Kennedy Space Center.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Harold L. Gier
Aerospace Design and Development
PO Box 672
Niwot, CO 80544-0672
Telephone No: (303) 530-2888

Refer to KSC-11683

NASA Tech Briefs Magazine

This article first appeared in the November, 1999 issue of NASA Tech Briefs Magazine.

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