Direct-reading air quality instruments or monitors provide information at the time of sampling, enabling rapid decision-making. These instruments provide the trained and experienced user the capability to determine if site personnel are exposed to airborne concentrations which exceed instantaneous exposure limits for specific hazardous air contaminants. Air quality monitors can be useful in identifying oxygen-deficient or oxygen-enriched atmospheres, immediately dangerous to life or health conditions, elevated levels of airborne contaminants, flammable atmospheres, and radioactive hazards. Direct reading instruments are particularly useful for identifying point source contamination or emissions such as gas leaks. Periodic monitoring of airborne levels with a real-time monitor is often critical, especially before and during work activities. Direct-reading instruments are useful for performing screening surveys to determine areas where additional evaluation is warranted.