The Organic Vapour Monitor 3500B uses a single charcoal sorbent wafer for collecting organic vapours. Accuracy of +/-25% at a 95% confidence level for many workplace contaminants. The Organic vapour Monitor 3500 uses the proven scientific principle of diffusion, which is the gradual mixing of molecules of two or more substances. It has a single charcoal sorbent wafer for easy collection of organic vapours and can be used for most applications. It has an 18-month shelf life.