LPS 1280 Issue 1.1 Testing procedures for the LPCB approval and listing of duct smoke detectors using point smoke detectors

This standard specifies requirements, test methods and performance criteria for duct smoke detectors that consist of a point smoke detector inside a sampling unit. The function of duct smoke detectors is to detect smoke in ventilation ducts in order to prevent the spread of smoke in a ventilation system. The sampling unit draws air from the duct by differential pressure arising from the airflow in the duct. The point smoke detector shall comply either with 54-73 or Annex D of this standard.

Although this standard covers duct smoke detectors that include electronics associated with the operation of dampers and or shutters to isolate the fire and prevent the spread of smoke within a building, it does not specify the requirements for the functions implemented by such units.

For duct smoke detectors working on different principles, or duct smoke detectors incorporating point smoke detectors operating on a principle different from that specified in 54-73, this standard should only be used for guidance.

Fire sensitivity tests

To demonstrate that the duct smoke detector has adequate sensitivity to typical smoke types which can be present in duct applications.

Switch on the smoke tunnel and adjust the air velocity in the working section to that required for the test, allowing the air flow to stabilize for a minimum of 2 min.

Measurements during conditioning

The fire parameters, ya and ma within the working volume (see Fig. H2) shall be measured throughout the duration of each test fire and recorded, continuously or at least once per second, as a function of time from the start of the test.

The alarm signal given by the supply and monitoring equipment shall be taken as the indication that a specimen has responded to the test fire.

Record the time of response (alarm signal) of each specimen along with the fire parameters ya and ma at the moment of response.

Operating method and basic construction

The mechanical construction of the measuring ionization chamber is shown in Annex I.

The measuring device consists of a measuring chamber, an electronic amplifier and a method of continuously sucking in a sample of the aerosol or smoke to be measured.

The principle of operation of the measuring ionization chamber is shown in Figure C.1. The measuring chamber contains a measuring volume and a suitable means by which the sampled air is sucked in and passes the measuring volume in such a way that the aerosol/smoke particles diffuse into this volume. This diffusion is such that the flow of ions within the measuring volume is not disturbed by air movements.

The air within the measuring volume is ionized by alpha radiation from an americium radioactive source, such that there is a bipolar flow of ions when an electrical voltage is applied between the electrodes. This flow of ions is affected by the aerosol or smoke particles in a known manner. The relative variation in the current of ions is used as a measurement of the aerosol or smoke concentration.

The measuring chamber is so dimensioned and operated that the following relationships apply:


  • suction nozzle

  • assembly plate

  • insulating ring

  • air/smoke entry

  • outer grid

  • inner grid

  • a rays

  • a source

  • measuring volume

  • measuring electrode

  • guard ring

  • insulating material

  • windshield

  • electronics

Technical data

  1. a) Radiation source: Isotope: Americium Am241; Activity: 130 kBq (3,5 |jCi) ± 5%; Average a energy: 4,5 MeV ± 5%;

Mechanical construction: Americium oxide embedded in gold between two layers of gold, covered with a hard gold alloy. The source is in the form of a circular disc with a diameter of 27 mm, which is mounted in a holder such that no cut edges are accessible.

  1. Ionization chamber:

The chamber impedance (i.e. the reciprocal of the slope of the current vs voltage characteristic of the chamber in its linear region (chamber current < 100 pA)) shall be 1,9 x 1011 Q ± 5 %, when measured in aerosol- and smoke-free air at:

pressure: (101,3 ± 1) kPa;

temperature: (25 ± 2) °C;

relative humidity: (55 ± 20) %;

with the potential of the guard ring within ± 0,1 V of the voltage of the measuring electrode.

  1. Current measuring amplifier:

The chamber is operated in the circuit shown in Figure C.2, with the supply voltage such that the chamber current between the measuring electrodes is 100 pA in aerosol- or smoke-free air. The input impedance of the current measuring device shall be < 109 Q.

Suction system:

This annex covers the additional test schedule for assemblies that are not approved to EN 54-73.

Additional test schedule

The additional test schedule in Table A1 shall be applied where a duct smoke detector includes a detector assembly that has not been approved as an EN 54-73 point detector. When carrying out the tests on the duct smoke detector, they shall be performed according to the test limits applied within EN 54-73. Where the duct smoke detector has a removable detector assembly that can be tested as a separate unit, then the tests shall be applied exactly as described in EN 54-73. Where the tests can only be applied to the complete duct smoke detector, then the required measurements of the response threshold value shall be carried out in accordance with 5.1.5.

Fifteen specimens shall be provided. After the reproducibility test, the four least sensitive specimens (i.e. those with the highest response thresholds) shall be labelled 12, 13, 14 and 15 and the others shall be labelled 1 to 11 arbitrarily.

The following requirements shall be met:

  • Clause 4.7 – Protection against the ingress of foreign bodies
  • Clause 4.8 – Response to slowly developing fires
  • Clause 4.11 – Additional requirements for software controlled detectors

Annex E (informative) – Air leakage test apparatus

The diagram below is an example of the mounting method of the duct smoke detector to perform the air leakage test as described in Clause 5.1.6.


The hotplate shall have a 220 mm diameter grooved surface with eight concentric grooves with a distance of 3 mm between grooves. Each groove shall be 2 mm deep and 5 mm wide, with the outer groove 4 mm from the edge. The hotplate shall have a rating of approximately 2 kW.

The temperature of the hot plate shall be measured by a sensor attached to the fifth groove, counted from the edge of the hotplate, and secured to provide a good thermal contact.


The sticks shall be arranged radially on the grooved hotplate surface, with the 20-mm side in contact with the surface such that the temperature probe lies between the sticks and is not covered, as shown in Figure G.1.

Heating rate

The hotplate shall be powered such that its temperature rises from ambient to 600 °C in approximately 11 min.

Three mats, approximately 50 cm x 50 cm x 2 cm, of soft polyurethane foam, without flame-retardant additives and having a density of approximately 20 kg/m3, are usually found sufficient. However, the exact quantity of fuel may be adjusted to obtain valid tests.


The mats shall be placed one on top of another on a base formed from aluminium foil with the edges folded up to provide a tray.


The mats shall normally be ignited at a corner of the lower mat, however the exact position of ignition may be adjusted to obtain a valid test. A small quantity of a clean burning material (e.g. 5 cm3 of methylated spirit) may be used to assist the ignition.

End of test condition

The end-of-test condition, mE, shall be when m = 0.7 dB/m in the duct tunnel working volume (see Figure I.2) or the specimen has generated an alarm signal, whichever is the earlier.

Test validity criteria

The development of the fire shall be such that the curves of m against y and m against time, t, fall within the limits shown in G.1 and G.2.

LPS 1280 Issue 1.1 Testing procedures for the LPCB approval and listing of duct smoke detectors using point smoke detectors

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