Particle Detectors: (4.26) Smoke Detector: (2) Design: (2. 5) Performance Differences: Smoke Alarm Standards be Trusted?' The speech concluded with a request for one of the world's largest ionization smoke alarm manufacturers and the CSIRO to disclose the level of visible smoke the manufacturers' ionization smoke alarms activate under CSIRO testing. According to fire tests conformant to EN 54, the CO2 cloud from open fire can usually be detected before particulate. Due to the varying levels of detection capabilities between detector types, manufacturers have designed multi-criteria devices which cross-reference the separate signals to both rule out false alarms and improve response times to real fires. Examples include Photo/heat, photo/CO, and even CO/photo/heat/IR. Obscuration is a unit of measurement that has become the standard definition of smoke detector sensitivity. Obscuration is the effect that smoke has on reducing sensor visibility; higher concentrations of smoke result in higher obscuration levels. The following is typical smoke detector obscuration ratings: (1) Detector Type: Ionization, Obscuration Level: 2. 6–5. 0% obs/m (0. 8–1. 5% obs/ft); (2) Detector Type: Photoelectric, Obscuration Level: 6. 5–13. 0% obs/m (2–4% obs/ft); (3) Detector Type: Beam, Obscuration Level: 3% obs/m (0. 9% obs/ft); (4) Detector Type: Aspirating, Obscuration Level: 0. 005–20. 5% obs/m (0. 0015–6. 25% obs/ft); (5) Detector Type: Laser, Obscuration Level: 0. 06–6. 41% obs/m (0. 02–2. 0% obs/ft