BS EN 14459:2021 pdf free download – Safety and control devices for burners and appliances burning gaseous or liquid fuels一 Control functions in electronic systems – Methods for classification and assessment.
b) In this step the sources and sub-sources of the basic hazards are identified. Basic hazards can have various sources each of their own and individual origin. Furthermore; each of these sources can have various sub-sources.
c) In this step the condition of the sources or sub-sources is identified in being normal or abnormal.
Abnormal condition is a condition of the appliance tinder the effect of a foreseeable but unlikely situation. This implies that following the abnormal condition the appliance remains safe.
List of examples of abnormal conditions (not exhaustive):
— line voltage larger than 0 V and smaller than (U — 15 %);
— line voltage above (U + 10 %);
— gas or oil pressure higher than 0 mbar and lower than I’mrn;
— gas pressure above pni
— blocked flue with regular maintenance;
— false flame simulation;
— tobecontinued.
Normal condition is a condition of the appliance under the effect of a foreseeable and likely situation. This implies that following the normal condition the appliance remains safe and functions correctly.
List of examples of normal conditions (not exhaustive):
— loss of line voltage;
— line voltage between 085 U and 1,1 U11
— gas or oil pressure between Pmin and pmax;
— loss of gas or oil pressure;
— lack of water pressure;
— blocked flue without regular maintenance;
— loss of flame;
— to be continued.
In this step the classification of the necessary protective measure is identified, making use of the described safety philosophy.
For classification of the protective measure, an abnormal condition is considered as a first fault. This means that for a normal condition, the protective measure is classified according to the basic hazard, and for an abnormal condition this protective measure may he classified one level lower than the basic hazard.
For background on realization of protective measures, see Annex CC.
BB.2 Risks
If one of the appliances, connected to the common flue, is not operating for some period, the exhaust gases in the overpressure exhaust flue, produced by the other appliances, tend to flow into this appliance.
The exhaust gases, coming into the appliance, will cool down and form condensate which may settle on parts in the appliance, such as electric wiring, printed circuit boards or control and safety devices.
The effect of condensation is unpredictable. it can be a short circuit, which may cause fire or damage a safety device, or a malfunctioning of a safety device, which may cause poisoning.
BB.3 Risk assessment
See Table BB.1.