The 3M™ Formaldehyde Monitor 3721 uses the proven scientific principle of diffusion, which is the gradual mixing of molecules of two or more substances. It monitors personnel or work areas in health care, laboratories and in the chemical, pulp/paper, foundry and textile industries. Analysis procedure is available upon request. The monitor uses a bisulfite-impregnated filter and is analyzed by colorimetry. The 3721 can be used for 8 hour TWA sampling to meet the OSHA requirement of +/-25% accuracy at 0.5-5.0ppm. However, this monitor does not have the sensitivity for short term exposure limit (STEL) monitoring. It has an 18-month shelf life.