The Non-Road Mobile Machinery (Emission of Gaseous and Particulate Pollutants) Regulations 1999

Calibration and span gases

1.2.2.  Mixture of gases having the following chemical compositions shall be available:

• C₃H₈ and purified synthetic air (see section 1.2.1)

• CO and purified nitrogen

• NO and purified nitrogen (the amount of NO₂ contained in this calibration gas must not exceed 5% of the NO content)

• O₂ and purified nitrogen

• CO₂ and purified nitrogen

• CH₄ and purified synthetic air

• C₂H₆ and purified synthetic air

Note: other gas combinations are allowed provided the gases do not react with one another.

• The true concentration of a calibration and span gas must be within ± 2% of the nominal value. All concentrations of calibration gas shall be given on a volume basis (volume percent or volume ppm).

• The gases used for calibration and span may also be obtained by means of a gas divider, diluting with purified N₂ or with purified synthetic air. The accuracy of the mixing device must be such that the concentration of the diluted calibration gases may be determined to within ±2%.