Cleanroom Particle Sampling Plan Calculator
Quality Assurance & Metrology: Calculate ISO 14644-1:2015 minimum sampling locations ($N_L$), sample volume ($V_s$), and sampling run duration per location.
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ISO 14644-1 Cleanroom Airborne Particle Classification
Cleanroom qualification and routine certification require an airborne optical particle counter (OPC) measuring particulate counts at statistically determined locations throughout the facility.
1. ISO Maximum Concentration Limits (Table 1)
The maximum particle concentration limit $C_{n,m}$ (particles per cubic meter) for target size $D$ is:
C_n,m = 10^N · ( 0.1 / D )^2.08
where $N$ is the ISO classification number ($1 \le N \le 9$) and $D$ is the threshold particle diameter in micrometers.
2. Minimum Single Sample Volume (Vs)
Per ISO 14644-1:2015 Clause B.4.2:
V_s (Liters) = ( 20 / C_n,m ) · 1000 [Minimum allowable V_s = 2.0 Liters]
Frequently Asked Questions
How did ISO 14644-1:2015 change cleanroom sampling location rules?
The 1999 standard used the simplistic formula $N_L = \sqrt{\text{Area}}$. The updated 2015 revision replaced this with a statistically rigorous hypergeometric probability model (Table A.1), which ensures with $95\%$ confidence that at least $90\%$ of the cleanroom clean zone complies with the target classification.
What is the "20-Particle Rule" for minimum sample volume?
To guarantee statistical validity and prevent Poisson counting uncertainty from falsely failing a compliant room, ISO 14644-1 Clause B.4.2 mandates that the sample volume $V_s$ must be large enough that at least 20 particles would be counted if the room were exactly at its classification limit: $V_s = (20 / C_{n,m}) \times 1000\text{ Liters}$, with an absolute minimum of $2.0\text{ Liters}$.
Why are 1.0 CFM (28.3 L/min) particle counters preferred for ISO Class 5 certification?
In ISO Class 5 ($3,520\ \text{particles/m}^3$), the required minimum sample volume is $5.68\text{ Liters}$. A $1.0\text{ CFM}$ ($28.3\text{ L/min}$) counter samples this volume in just $12\text{ seconds}$ (standardly rounded to $1\text{ minute}$ / $28.3\text{ L}$ for robust statistics). In contrast, an inexpensive handheld $0.1\text{ CFM}$ ($2.83\text{ L/min}$) sensor requires over 2 minutes per point, making whole-facility surveys impractically slow.