ISO 21927-4:2019 pdf free

ISO 21927-4:2019 pdf free.Smoke and heat control systems一Natural smoke and heat exhaust ventilators一Design,requirements and installation
The duration of fire growth to be assumed for the purposes of this document (see Table 2) is the time that elapses between the outbreak of a fire and the start of firefighting measures.
The time that elapses between the outbreak of a fire and the alarm being raised shall be taken as 10 min.This period of time does not apply where fire alarm systems incorporating automatic fire detectors activated by smoke have been installed. The fire alarm shall be transmitted to a fire station or other station that can provide assistance and is manned around the clock.
It does not apply either to spaces that are continuously manned, ensuring that any fire is detected immediately and the fire service notified accordingly.
It shall be taken as 5 min where NSHEVs are fitted with automatic fire detectors activated by smoke.In such cases, it is sufficient to install one smoke detector per every 200 m2 of the smoke reservoir. A distance of 10 m between beams is sufficient for linear smoke detectors.
A mean time of 10 min shall be assumed for the time that elapses between the fire alarm being raised and the start of firefighting measures. In favourable circumstances, such as where there are on-site firefighters who can reach the scene of a fire in less than 5 min, it may be reduced to 5 min. The mean time shall be increased to 15 min if the circumstances are unfavourable and to 20 min if the circumstances are exceptionally unfavourable.
The times referred to in this clause are auxiliary design values and are only to be used when calculating the fire growth rate needed for the purposes of this standard.
Generally, the values given in the column “average” of Table 2 shall be used. The values given in the column “particularly low” may be used for particularly low fire propagation rates (e.g. combustible materials in non-combustible packaging) while those in the column “particularly high” shall be used for particularly high fire propagation rates (e.g. readily flammable materials in combustible packaging).In cases in which design group 4 or 5 is obtained from Table 2, design group 3 may be used without further verification if an automatic sprinkler system covering the entire area has been installed.ISO 21927-4 pdf free download.