The standards ISO 14520 (EN 15004) and NFPA 2001, pursuant to which fixed fire extinguishing systems are designed, stipulate the requirements for a minimum hold time of gas concentrations in the protected zone.

The minimum gas hold time in the protected zone may be checked in two ways::

  • by discharging the gas in the protected zone and measuring the concentration of gas over a 10-minute period, or
  • by conducting a door fan test (ISO 14520 – Annex E / NFPA 2001 – Annex C)

A door fan test is conducted by means of special “Blower Door” equipment comprising the blower, measuring equipment and software. The blower is used to generate overpressure in the protected zone, then negative pressure. Special measuring equipment and the relevant software are used to carry out the readings to obtain output data compliant with the standard EN 13829. The output data obtained by measurement are entered in the special software which calculates the results under the standards ISO 14520 (EN 15004) and NFPA 2001. The final software output is the hold time of gas in the protected zone. If gas hold time is not compliant with the standards, the anemometer is used to establish leakage pathways which are sealed and the door fan test is repeated.