Key Terms

Assigned protection factor (APF): This is a value given to each type of respirator that can help determine the maximum concentration of a given hazard that the respirator can protect against.

Fit factor: This value describes how well a particular respirator fits and is determined by quantitative fit testing.

Maximum use concentration (MUC): This value is determined by multiplying the assigned protection factor of a respirator by the permissible exposure limit of an atmospheric hazard. It describes the maximum concentration of a hazard that the respirator can protect against.

Negative pressure mode: A respirator in negative pressure mode allows air to enter the facepiece only when the user creates negative pressure by inhaling. The terms "negative pressure mode" and "demand mode" are used interchangeably throughout this course.

Positive pressure mode: A respirator in positive pressure mode supplies air even when the user is not inhaling, creating positive pressure within the facepiece. The terms "positive pressure mode" and "pressure-demand mode" are used interchangeably throughout this course.

Permissible exposure limit (PEL): This is the maximum concentration of a substance that can be present in the air before respiratory protection is necessary. This value is usually measured in micrograms per cubic meter, or in parts per million.

Respiratory inlet covering: This is the part of a respirator that forms a barrier between the user and the surrounding hazardous atmosphere; also known as a facepiece.

Respiratory system: This is the set of organs that allows the human body to intake oxygen into the body, where an exchange of oxygen and carbon dioxide takes place. In mammals, the respiratory system includes the nasal passages, pharynx, trachea, bronchi, and lungs. The respiratory system is the set of organs that allows a person to breathe and exchange oxygen and carbon dioxide throughout the body.

To learn more about Respiratory Protection visit our Cal/OSHA Respiratory Protection Online Training web page.