Face masks with filter cartridges are currently used to protect individual workers exposed to organic solvents. The lack of a service-life indicator, however, puts workers at risk of poisoning when the filter cartridge becomes saturated. To correct this problem, researchers evaluated the effectiveness of a fibre-optic sensor consisting of an absorbent tube that emits a signal when it has absorbed a quantity of pollutants corresponding to the lifespan of the filter cartridge. The fibre-optic system was incorporated into filter cartridges and laboratory-tested to determine its response to variations in air flow, humidity, and the concentration of one or more contaminants. The results indicate that the system is effective, but requires further development to improve its sensitivity to solvents.