The stainless steel sampling heads for Contact Plates (RODAC) or Petri dishes are manufactured of AISI stainless steel and are drilled with holes 1 mm in size. The operators can interchange these heads with no difference in air flow on an air sampler regardless of which head is used, as long the recommended procedures below are followed.
The aspirating heads are machined starting from a sheet of stainless steel. The tolerances on all the manufactured heads are strictly controlled and each head is delivered with a Certificate of Manufacture, referencing from current manufacturing batches. The document reporting the number of holes and the size of the holes is signed by the qualified technician performing the work. The tolerance in air flow is less than +/-1%.
The operator may interchange the stainless steel heads across his air samplers with confidence that there is no consequential difference in air flow from head to head, with the one caveat that the ensures the head holes are routinely inspected to be sure they are clean. While these heads need not have been individually calibrated within the recommended 6 months calibration interval of the individual air samplers, the head must be inspected prior to being interchanged. While unusual, it is possible for a lab to get prepared media inside holes or powder affiliated with the product being quality controlled.
The stainless steel aspirating head should not be treated with caustic liquid products or aggressive chemicals but only with detergent or disinfectant that do not contain chlorine. In fact it is very well known that chlorine detergent may produce after some time rust. It is strongly recommended to clean and sanitize the surface of the head spraying a 70% sterile alcoholic solution.