Posted By Paul Leadbetter
Adam

MDHS 14/3, like all such methods, represents current best practice but is not legally binding. 14/3 states that the lower limit of detection for gravimetry should be an order of magnitude lower than the appropriate exposure limit. The limit of detection will depend, in part, on the sensitivity of the balance used. Therefore, you should ensure that the sensitivity is appropriate for the dusts you are trying to measure. For example, if you are measuring non-toxic dusts (nuisance dust), you need to able to measure down to 1 mg/m3 but, if you are measuring, say, nickel dust, you need to be able to measure down to 0.01 mg/m3.

Regards

Paul Leadbetter

Posted By Simon Wilkins
Adam,
The number of decimal places does not necessarily reflect accuracy - 0.00002, 0.2 and 200 are all measurements accurate to one significant digit. Likewise 0.00345, 0.345 and 345 all suggest three digit accuracy. If you are measuring a dust concentration (weight per volume) then you should only quote a figure to an accuracy reflecting the least accurate part of measurements. Anything else is suggesting a spurious accuracy.
There is absolutely no point in paying for great accuracy in the weighing if this is not matched by the accuracy of the volume measurement. Our own lab can almost cetainly weigh more accurately than your volume measurement technique which may only be accurate plus or minus a few percent.