about 150mm in order to obtain satisfactory extraction of air from the zone immediately above the hob into the hood more specifically with known air extraction hoods a large percentage typically 80 of the air drawn into the hood is external air ie not drawn in from the zone immediately above the hob 14 the conduit 26 and air extraction means must thus be oversized in order to handle this excess air as well as the contaminated air from the zone immediately above the hob 14 this disadvantage is to a large extent obviated with the hood 12 where substantially all the air drawn into the hood is from the zone immediately above the hob 14 as a result of the laminar flow induced along the concave surface 58 of the passageway wall 48 additionally with known air extraction hoods it is normally necessary that the leading edge of the front panel thereof be located a minimum distance from a floor to provide the necessary heads or movement space for people using cooking apparatus with the hood 12 this minimum distance is no longer necessary and the hood 12 can thus be located at a lower level so that it can be used in more confined spaces with reference to fig3 reference numeral 300 generally indicates an air extraction hood according to a second embodiment of the invention parts of the hood 300 which are the same or similar to those of the hood 12 are indicated with the same reference numerals the hood 300 is thus very similar to the hood 12 save that its front panel 20 is much narrower with the roof panel 22 having a downwardly forwardly sloping portion 302 typically the maximum depth of the hood 300 is about 700mm the maximum distance it.