# Experimental Study on Particle Size Distribution Characteristics of Aerosol for Fire Detection
## 2 Materials and Methods  
In order to exclude interference from non-fire aerosols, an aerosol experimental platform is set up to study differences in the particle size distributions of typical fire smokes and non-fire aerosols, as shown in Figure 1. According to the block diagram illustrated in Figure 2, the platform consists of an aerosol generator and storage module and a particle sizing module.  
In the aerosol generator and storage module, there are three different types of aerosol chambers for fire smokes, dust samples, and spray aerosols, correspondingly. Fire smokes are generated by corresponding smoke generators and stored in a 50 cm \(\times\) 50 cm \(\times\) 50 cm smoke chamber. Specifically, smoldering cotton and smoldering wood are heated by an electric heater, where the power of the heater is well controlled to ensure that the combustibles are always in a state of smoldering combustion; open fire of Polyurethane and open fire of N-heptane is held in a heat-resistant, wide-mouth container and ignited with open fire. A pair of 12 cm diameter fans are installed diagonally on the smoke chamber to ensure that the smoke concentration is evenly distributed throughout the chamber. An air bag, which is connected to the external air through a pipe, is equipped to ensure the air pressure balance in the smoke chamber and the stable concentration of smoke particles during aerosol sampling procedure.  
Dust experiments are conducted in a transparent sphere of 0.3 m radius. The standard dust is held on the bottom of the sphere chamber, where a turbine fan with 13,500 rpm is installed at a 10 cm height from the bottom to blow up the dust. The sampling port at the top of the spherical chamber is connected to the particle size measurement equipment for dust sampling.  
The fog cabinet is used to simulate water mist interference. This equipment uses high-pressure airflow to atomize the water and release it from the nozzle to the whole box. An exhaust port at the back of the cabinet is used to sample the water mist to the aerosol particle size analysis system.  
In the aerosol particle sizing module, SMPS, APS (Aerodynamic Particle Size, TSI APS-3321, TSI Incorporated, St. Paul, MN, USA), and HELOS (Helium-Neon Laser Optical System, Sympatec HELOS/RODOS, Sympatec GmbH, Clausthal-Zellerfeld Germany) are used to obtain the particle size distribution information for typical fire smokes and non-fire aerosols. The measurement range of SMPS 3936 is 0.02-1 \(\upmu\)m, while that of APS 3321 is 0.5-20 \(\upmu\)m. Although their measurement principles are different, the results of these two instruments can be merged to achieve a wide particle size range of 0.02-20 \(\upmu\)m for measuring fire smokes and non-fire aerosols. HELOS provides non-contact measurement of the particle size distribution in real-time based on Fraunhofer diffraction, which is suitable for measuring water mist and oil spray. Depending on the lens selected, our HELOS has a measurement range of 0.1-35 \(\upmu\)m. Thus, based on these aerosol particle size measurement instruments, our experimental platform is able to measure the particle size distribution and concentration of typical fire smoke and non-fire aerosols.