The sealed compartments (also called superstructures) installed on the chassis had floor openings – about 60 millimetres (2.4 in) in diameter – with metal pipes welded below, into which the engine exhaust was directed.[16] The exhaust gases causing death by asphyxia were tested by a chemist from the mass murder operation Action T4 to make sure they contained large enough amounts of carbon monoxide (or 1% concentration), to form carboxyhaemoglobin, a deadly blood agent, in combining with haemoglobin in the cells. The victims were thereby deprived internally of life-giving oxygen before death.[16]