From the changes in ISO14644-1:2015

Taking into account the new theory of spatial distribution of particles, ISO14644-1 has made major changes in the number of sampling points. Combined with the specific content of the standard, we can see the following changes.

Number of sampling points

From the comparison of the following figure, we can see that the general trend is: the number of sampling points for 6-1000 square meters has increased, and the number of sampling points for 1000 square meters has decreased. Of course, it must be pointed out that the minimum number of sampling points is listed in the table. If the risk points are obtained by combining the company's production process and historical data, the number of sampling points can be increased.

Question: Whether the sampling point location needs to be marked and numbered on the workshop drawing must be clear. The sampling point here refers to the sampling point of dust particles. If it is only for the purpose of detection, how to make the sampling point more realistically reflect the distribution of dust particles in the room is the key point of the problem, that is, representativeness. The standard mentions the method of equal area blocks. Combined with actual operation, non-unidirectional flow rooms must also consider the airflow pattern to avoid the direct air supply position of the high-efficiency filter (directly below or other). Marking the sampling point location on the drawing is to illustrate representativeness.

The role of numbering is more of a traceability requirement. Because in many cases the location of the sedimentation bacteria will be consistent with the location of the dust particle sampling point, the culture results can draw a "pollution map".

Calculation and judgment of results

In most cases, UCL needs to be calculated, and sometimes each result is qualified but the UCL value is unqualified. The new change is to directly calculate the average value, which simplifies the calculation process.

Result judgment: The multiple data of each sampling point are directly averaged, the average value is qualified, and the sampling point meets the requirements. Even if some individual data exceeds the limit range, as long as the average value is qualified.

Sampling time or sampling volume needs to be calculated

The single sampling volume is at least 2 liters, and the sampling time is at least 1 minute. This part of the content occupies a relatively large space in the new version of the standard. In order to cover various situations that may occur, the standard setters have given examples, which reflects good intentions. However, if you look through it, you can also find a pattern. For the dust particle counter with a flow rate of 2.83L/min, it is indeed necessary to calculate each time. Even if the dust particle counter with a flow rate of 28.3L/min, 50L/min and 100L/min is iso 5 (AB or 100), 1 minute should be able to cover it perfectly. Of course, for a fixed factory, it only needs to be calculated once, which can be fully implemented in internal documents.

New standard for measurement of dust particle counters ISO 21501-4

In the old version of the standard, the frequency and method of measurement of dust particle counters need to comply with the existing common standards. But there is no specific mention of what standard it is. In the measurement reports of dust particle counters in the past few years, I can only see the confirmation of standard particles and sampling volume.

In ISO 21501-4, regulations are made for four different principles of particle counters. The most commonly used is the light scattering aerosol particle counter. The standard mentions the following items that need to be measured:

• Sampling flow

• Counting efficiency

• Resolution

• False counting rate

• Particle size setting

• Maximum particle concentration consistency loss

• Maximum particle number concentration

• Sampling time

• Reaction speed