Permeation of chemicals through the walls of air-supply hoses used with respirators is an under-recognised problem in industry. Transport of chemicals through the wall of a hose occurs in the same manner as through gloves and chemical suits, driven by the chemical concentration gradient, but for air-supply hoses the chemical evaporating inside the air-supply hose is inhaled. A simple method based on the mathematical equivalence of filling a hose with a chemical to immersing it in a chemical has been developed. The method requires a short section of hose to be filled, plugged and weighed at intervals to determine the breakthrough time and permeation rate per meter. The method has been validated experimentally and calculations show that permeation through the walls of a hose can dominate the respiratory dose, particularly with a hose