model for system sizing. for example, this is a requirement for all public water systems in the united states per the epa uv manual.: 5–2 the flow profile is produced from the chamber geometry, flow rate, and particular turbulence model selected. the radiation profile is developed from inputs such as water quality, lamp type (power, germicidal efficiency, spectral output, arc length), and the transmittance and dimension of the quartz sleeve. proprietary cfd software simulates both the flow and radiation profiles. once the 3d model of the chamber is built, it is populated with a grid or mesh that comprises thousands of small cubes. points of interest—such as at a bend, on the quartz sleeve surface, or around the wiper mechanism—use a higher resolution mesh, whilst other areas within the reactor use a coarse mesh. once the mesh is produced, hundreds of thousands of virtual particles are "fired" through the chamber. each particle has several variables of interest associated with it, and the particles are "harvested" after the reactor. discrete phase modeling produces delivered dose, head loss, and other chamber-specific parameters. reduction equivalent dose when the modeling phase is complete, selected systems are validated using a professional third party to provide oversight and to determine how closely the model is able to predict the reality of system performance. system validation uses non-pathogenic surrogates such as ms 2 phage or bacillus subtilis to determine the reduction equivalent dose (red) ability of the reactors. most systems are validated to deliver 40 mj/cm2 within an envelope of flow and transmittance. to validate effectiveness in drinking water systems, the method described in the epa uv guidance manual is typically used by us water utilities, whilst europe has adopted germany's dvgw 294 standard. for wastewater systems, the nwri/awwarf ultraviolet disinfection guidelines for drinking water and water reuse protocols are typically used, especially in wastewater reuse applications.