What the public evidence supports
The current research pack records German drainage rules that use 22 % methane for automatic compressor shutdown and 30 % for a warning. A separate New Zealand government investigation records that drainage gas should not be diluted below 30 % methane. These are reference points for engineering discussion, not universal thresholds.
At 22 %vol, an accuracy stated as ±4–6 % of reading corresponds to approximately ±0.88–±1.32 %vol. Whether that error band is acceptable depends on the actual interlock design and the applicable rule set.
Put the error band at the decision point
- Name the threshold and action: warning, shutdown or another system response.
- Use the accuracy expression that applies at that concentration, not only a full-scale percentage.
- Include pressure, temperature, gas composition, flow and response definition.
- Confirm the rule set and host-system logic for the target jurisdiction.
A narrow measurement error band improves one input. It does not by itself prove correct installation, system logic, EMC, intrinsic-safety association or legal compliance.
FAQ
Questions engineers ask next
Are 22 % and 30 % legal thresholds everywhere?
No. They are documented reference points. The threshold and action for China, Poland, Russia or another jurisdiction must be confirmed from the applicable rule set and host system.
Does a narrow error band automatically make the system safe?
No. It improves one measurement input. The complete system still requires correct installation, association, EMC, logic, testing and maintenance.
Why can a falling methane reading be critical?
In high-concentration drainage gas, the gas is intended to remain above the explosive range. A fall toward that band can change the process and safety decision, unlike ordinary low-range ventilation monitoring.
What should the host team provide?
The host team should provide the threshold logic, action, jurisdiction, installation conditions and evidence requirements against which the module reading will be evaluated.