Zero is not a universal certificate
The class applies to a specific contaminant group. Class 0 for oil alone therefore says nothing about water and particles. For a machine declaration, check its scope and test conditions; do not automatically extend it to pipework where additional contamination can arise.
How to write a verifiable specification
Specify the limit, components measured, reference conditions, sampling point, operating states and measurement method. For oil, the sum of liquid, aerosol and vapour is relevant. The requirement must be measurable with an appropriate limit of quantification and uncertainty assessment.
What to check in practice
- State which contaminant requires class 0.
- Write specific stricter values instead of the word “zero”.
- Verify purity after the complete treatment system and at the relevant point of use.
Example scenario
An illustrative “Class 0 oil” requirement supplemented by a limit of 0.005 mg/m³ is stricter than the oil class 1 limit. Measuring vapour alone is not enough, however; total oil contamination and the measurement's ability to reliably assess that limit must be addressed.
What to watch out for
- Interpreting Class 0 as zero of every contaminant.
- Confusing an oil-free design with the quality of the entire system.
- Using “below detection” without specifying the detection limit.
Is [0:0:0] a sufficient specification?
Not without additional limits. Particles, water and oil must be defined separately, together with how they will be assessed. If the process has specific requirements for microorganisms or other gases, add those too.