HAZARD - Slight

DETECTION - Blackened thermometer, thermistor.

USES - Heating, thermal imaging

Sources of infrared

All objects continually emit energy as electromagnetic radiation. The range of wavelengths emitted depends essentially on the temperature of the object. As the temperature increases the object emits more energy at each wavelength and the peak emission moves to shorter wavelengths. At ambient temperatures almost all the radiation is in the infrared region and hardly any in the visible region. We detect infrared radiation as warmth, e.g. from a fire.

Thermal images are put to many different uses in many different areas. These include medicine since diseased parts of the skin are often hotter. Circulation problems and inflamed joints are also investigated using the technique. Most well known is the detection of survivors in earthquake debris, and in large buildings that are burning. The electrical supply industry also uses the technique to detect objects before they become irreparable. More sophisticated uses include energy conservation studies, meteorological, ecological and geological surveys.

Most objects emit measurable amounts of infrared radiation in the range 2 x 10-6 m to 40 x 10-6 m but some of this is reduced as it passes through the atmosphere by absorption and scattering. The scattering is due to the presence of particles. However, if their size is smaller than the wavelength of the radiation, scattering is negligible. Smoke and light mist particles fall into this category. The larger particles in rain and fog, however, produce significant scattering in both the infrared and visible regions. Much more important is absorption by molecules of gas that exist in the atmosphere, especially water and carbon dioxide.