RCRA
Resource Conservation and Recovery Act of 1976. (US Environmental Protection Agency)

Reactivity (chemical)
A substance’s susceptibility to undergo a chemical reaction or change that may result in dangerous side effects, such as an explosion, burning, and corrosive or toxic emissions.

Respirable size particulates
Particulates in the size range that permits them to penetrate deep into the lungs upon inhalation.

Respirator (approved)
A device which has met the requirements of 30 CFR Part 11 and is designed to protect the wearer from inhalation of harmful atmospheres and has been approved by the National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA).

Respiratory system
Consists of (in descending order) - the nose, mouth, nasal passages, nasal pharynx, pharynx, larynx, trachea, bronchi, bronchioles, air sacs (alveoli) of the lungs, and muscles of respiration.

Route of entry
The path by which chemicals can enter the body. There are three main routes of entry: inhalation, ingestion, and skin absorption.