A system (1; 201) for monitoring the exposure of a plurality of individuals to a physical or chemical property associated with an environment, the system comprising: a plurality of portable devices (9; 301), wherein each portable device is arranged to be worn or carried by an individual in the environment; and a control unit (7; 209) for communicating with each of the plurality of portable devices; wherein each portable device comprises: a detector arranged to measure a physical or chemical property that the individual wearing or carrying the device is exposed to in the environment; one or more physiological sensors (11, 12, 13) each arranged to measure a physiological parameter of the individual; a geolocation module (14, 15) arranged to determine the location of the individual; and a communication module for communicating data collected by the portable device with other(s) of the plurality of the portable devices and with the control unit; the system being characterized in that it further comprises a plurality of triangulation beacons positioned in fixed locations around the environment, wherein each triangulation beacon is arranged to transmit a wireless signal to the plurality of portable devices in the environment, and each geolocation module comprises a receiver arranged to receive the wireless signals transmitted by the triangulation beacons, wherein the geolocation module is arranged to use the received wireless signals to determine the location of the individual; and wherein at least one of the plurality of triangulation beacons comprises at least one additional detector arranged to measure a chemical and/or a physical property associated with the environment. a plurality of portable devices (9; 301), wherein each portable device is arranged to be worn or carried by an individual in the environment; and a control unit (7; 209) for communicating with each of the plurality of portable devices; wherein each portable device comprises: a detector arranged to measure a physical or chemical property that the individual wearing or carrying the device is exposed to in the environment; one or more physiological sensors (11, 12, 13) each arranged to measure a physiological parameter of the individual; a geolocation module (14, 15) arranged to determine the location of the individual; and a communication module for communicating data collected by the portable device with other(s) of the plurality of the portable devices and with the control unit; a detector arranged to measure a physical or chemical property that the individual wearing or carrying the device is exposed to in the environment; one or more physiological sensors (11, 12, 13) each arranged to measure a physiological parameter of the individual; a geolocation module (14, 15) arranged to determine the location of the individual; and a communication module for communicating data collected by the portable device with other(s) of the plurality of the portable devices and with the control unit; the system being characterized in that it further comprises a plurality of triangulation beacons positioned in fixed locations around the environment, wherein each triangulation beacon is arranged to transmit a wireless signal to the plurality of portable devices in the environment, and each geolocation module comprises a receiver arranged to receive the wireless signals transmitted by the triangulation beacons, wherein the geolocation module is arranged to use the received wireless signals to determine the location of the individual; and wherein at least one of the plurality of triangulation beacons comprises at least one additional detector arranged to measure a chemical and/or a physical property associated with the environment.