Particle masks and medical masks can be used to reduce exposure to different types of respiratory threats. One example is the eruption of Mount Saint Helen volcano. In the aftermath of that event, particle masks were used to protect people from dangerous volcanic ash. During the 9/11 attack on New York, particle masks reduced later illness due to toxic dust. Medical masks can reduce exposure to dangerous flu viruses. Some of these viruses can reach pandemic status. Masks rated N95 or higher can dramatically reduce exposure to these viruses.