The BG 174 provides 4 hours of breathing air.  

This example was used by mine recue at Posgold Operations Tennant Creek, Northern Territory, Australia. Each BG 174 cost around AU$10,000 to purchase and were originally used with a mouth piece and goggles before later being replaced by the Panorama nova ZS & ZST masks. The mine rescue replaced the BG 174s with BG 4s in 2004 at a cost of approximately AU$8,000 each.