The European Spallation Source (ESS) proton accelera- tor will be a multi-MW proton linear accelerator and will require a very carefully designed beam loss monitoring (BLM) system. Slow, continuous losses will have to be monitored and kept low enough to allow hands-on main- tenance of the machine. Fast and large losses will have to be prevented by sending a beam-abort signal to the con- trol system. This paper gives a conceptual design of the ESS BLM system; it describes the detectors planned at ESS and discusses their quantity and positioning. An ionization chamber (IC) was chosen as a primary detector for mea- suring the losses. The design parameters of the detector are given based on the response time considerations. The results for the response functions of the new detector as a function of the incident particle type, angle and energy are presented.