Concentric air diffuser with an angled supply air face

A method for conveying air through a concentric air diffuser, the method comprising:

• providing an inner surround structure that channels ingoing air of the concentric air diffuser, wherein the inner surround structure comprises a smoke pan and at least one collar attached to the smoke pan;
• providing a central air diffuser to diffuse the ingoing air to the inner surround structure;
• providing a smoke detector including a sampling tube;
• providing an outer surround structure that channels outgoing air of the concentric air diffuser;
• providing at least one supply air diffuser to diffuse the outgoing air to the outer surround structure;
• and
• mounting the smoke detector to the inner surround structure such that a sampling tube of the detector extends into the smoke pan and is centrally aligned with respect to the at least one collar and the sampling tube of the detector is accessible through a single sampling tube access door on the smoke pan, wherein the sampling tube access door is non permeable to air.