The Low-altitude Escape Harness is, as its name implies, a piece of emergency-escape equipment used by International Rescue.
This jetpack-like device, worn on one's back, launches the person wearing it up into the air, once the activation pin is pulled. He, or she, will then have a slow and safe descent to the ground (see photo gallery, below).
In the episode Edge Of Impact, Virgil and Alan Tracy use this method to rescue two men - Jim and Stan - left trapped atop the British Telecom Tower, after a runaway jet crashed into it and no other means of reaching them was possible.
In a drenching downpour, Alan uses the Booster Mortar to sharp-shoot two metal capsules - each containing a low-altitude escape harness - through the window of the tower's control room, where Jim and Stan strap them on and then leap to safety before the tower collapses.