Deposit Thickness TestThe Deposit Thickness Test is a method for determining the dirtiness or cleanliness of a system. This is done by use of an electromagnetic induction type thickness gauge, which was developed within the coatings industry. The system uses a non-contact measuring tip inside a protective head. The thickness of dust contamination on the internal surfaces of a ventilation system is measured to an accuracy of +/- 3 microns. The measurements recorded provide valuable information relating to system cleanliness or dirtiness and ultimately system safety. The results of the tests are compared to the guidance levels set in HVCA’s TR19 and relevant actions taken, such as cleaning or continued monitoring. It is recommend that testing be carried out on an annual basis. Recommended Test Locations: - HVCA recommends not less than one test point every 50 linear metres of ducting up to 300m and not less than 100m test intervals thereafter.
- Average deposit thickness should be reported to determine whether it is appropriate to clean the system.
- Individual excessively high results may indicate the need for local cleaning.
TR19 Section 5 Surface Deposit Limits, Table 5
System Type | Surface
Contaminant Limits | Test Method
(V.T. Vacuum test) | Extract | 6g/m 2
180µm | V.T.
D.T.T. | Re-circulation | 1g/m 2
60µm | V.T.
D.T.T. | Supply | 1g/m 2
60µm | V.T.
D.T.T. |
 The levels given in Table 5 are based on current good practice. They take away the subjectivity of a visual inspection.
Clearwater recommend that regular system measurements should be supported with a visual inspection and a report on internal system conditions.
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