This monitor meets OSHA accuracy requirements of +/-25% for 8-hour TWA sampling of formaldehyde. Not for 15 minute STEL sampling. Analysis not included. 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,