Article Performance of an N95 Filtering Facepiece Particulate Respir...

An N95 respirator is a respiratory protective device designed to achieve a very close facial fit and very efficient filtration of airborne particles. Note that the edges of the respirator are designed to form a seal around the nose and mouth. Surgical N95 Respirators are commonly used in healthcare settings and are a subset of N95 Filtering Facepiece Respirators (FFRs), often referred to as N95s.

N95 respirators and surgical masks are examples of personal protective equipment that are used to protect the wearer from airborne particles and from liquid contaminating the face. The Centers for Disease Control and Prevention (CDC) National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) also regulate N95 respirators.

It is important to recognize that the optimal way to prevent airborne transmission is to use a combination of interventions from across the hierarchy of controls, not just PPE alone.

For more detail please go through the site https://www.fda.gov/medical-devices/personal-protective-equipment-infection-control/n95-respirators-surgical-masks-and-face-masks#s1

You need to be trained to use properly & ideally have a face fit test eg not useful if you have a beard.

Good question

Here is some information to know more about N95 mask

https://m.timesofindia.com/life-style/health-fitness/health-news/government-issues-advisory-against-n95-masks-which-is-the-best-type-of-mask-to-protect-you-from-covid-19/amp_etphotostory/77262511.cms

N95 surgical mask example of personal protective equipment which is used to protect from the liquid contamination and airborne particles And for covid which can't be seen by naked eye so will not be effective for covid 19