What is dust concentration? In the clean room (area) how to sample, sampling points how uniform layout? How to determine the level of clean room (area)?

Refers to the volume or mass of suspended particulates in the air per unit volume.
When the unit of “grain / liter”, said the count concentration: When the unit in mg / m3 said, called the weight concentration.
In the clean room sampling, the sampling location should be 0.8m from the ground level of the surface evenly arranged. More than 5 points, but also from the ground 0.8m ~ 1.5m height of the region layered layout. Sampling should determine the air volume and pressure, while avoiding the return air. Clean indoor sampling point layout and strive to avoid sampling points in a local area sparse.
The clean room class is determined based on the following two conditions:
The average particle concentration of each sample point must be less than or equal to the prescribed level limit, ie Ai ≤ level limit.
The 95% confidence limit of the average of the particle concentration mean of all the sampling points must be less than or equal to the prescribed level limit, UCL≤ level limit.