The biggest difference between a respirator and a surgical mask is the intended use. Respirators are designed to help reduce the wearer’s respiratory exposure to airborne contaminants such as particles that are small enough to be inhaled - particles less than 100 microns (µm) in size. This includes airborne particles that may contain biological material, e.g. mold, Bacillus anthracis, Mycobacterium tuberculosis, the virus that causes Severe Acute Respiratory Syndrome (SARS), Avian Flu, Ebola Virus etc. or even PM2.5 / PM10. Surgical masks on the other hand do not have either adequate filtering or fitting attributes to provide respiratory protection for the wearer. They are designed to help prevent contamination of the work environment or sterile field from large particles generated by the wearer (e.g. spit, mucous). Surgical masks may also be used to help reduce the risk of splashes or sprays of blood, body fluids, secretions and excretions from reaching the wearer’s mouth and nose. Respirator types and standards For protection against volcanic ash, high-efficiency, light-weight disposable respirators are appropriate. The respirator must provide protection at the highest concentration the person will experience. Suitable disposable respirators are ‘CE’ marked to show that the design has been tested to a recognized standard. They will also be marked with the standard (e.g. EN 149:2001 in the EU or N95 in the US) and an additional code such as FFP2 (medium efficiency) or FFP3 (high efficiency) (FFP = Filtering Face Piece) is shown on EU respirators. The US N95 standard is roughly equivalent to FFP2 or 3 as it is efficient up to 10 x the local occupational exposure limit (see Table below). The higher the FFP number, the more protection the respirator can provide if it is used properly. Disposable respirators cover the nose, mouth and part of the chin. Some of them contain exhaling valves. An elastic band around the head and neck keeps them in place. Valved respirators are more comfortable, especially for those wearing spectacles which might otherwise mist up. They are appropriate for hot and humid climates.