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Infrared Radiation

Viimati uuendatud: 25.02.2017

Infrared Radiation

Infrared radiation is a natural part of the life and working environment of humans, thus, people are regularly exposed to it. For example, when exposed to sunlight, the infrared part of the light is sensed as warmth. When heating a (stone) oven, the infrared radiation is emitted from the heated stones. Also, when two or more people are close to one another, they feel the warmth (infrared radiation) radiating from others.

Several industrial processes require a strong heat, which increases the exposure of employees involved in these processes to the infrared radiation much higher than in the case of other industrial sectors. Such jobs include firefighting, baking, blowing glass, drying, burning, welding, casting, melting and other iron handling jobs. Also several industrial, medical and laboratory lasers emit a strong infrared radiation.

Table. Examples of job-related exposure to infrared radiation.

Infrared radiation (including infrared light) is invisible to the human eye starting from 780 nanometres (the last wavelengths that a human can see). A human can only sense a very small part (400-780nm) of the entire electromagnetic spectre with their eyes and people see this range as colours: violet, blue, green, yellow, orange, red.

People sometimes call the infrared radiation as heat radiation instead because a person can sense certain wavelengths of it on their skin as warmth.

Infrared light is divided (based on ISO 20473) into three areas (click on the image):

near infrared 0,78-3 μm, mid infrared 3-50 μm, far infrared 50-1000 μm.

Health Effects

As optic radiation does not penetrate deep into biologic tissues, most attention must be paid to eyes and skin. When exposed to infrared radiation, it mostly involves a thermal effect.

Eyes

In general, the human eye is well protected against the natural optical radiation, including Sun radiation. This protection also expands to bright artificial lighting. The radiation mostly affects the eye retina as the eye-internal substance lets light through. The transparency of the eye lense could decrease, when looking straight into a bright near infrared radiation source.

The eye lense is damaged on wavelengths below 3μm (bright near infrared and visible light). The longer the infrared radiation wavelength, the lesser it reaches the background of the eye. Mid and far infrared radiation absorbs in the cornea to the large extent. However, absorbing far infrared radiation in the cornea could lead to temperature growth in the eye. Similar to the effect on skin, the intensive far infrared radiation could cause eye cornea burns. However, such burns are rare because the pain reaction is usually triggered first. Heat-caused eye damage is for instance cataract (grey cataract), most common in glass blowers.

Infrared radiation does not reach very deep in a body. Therefore, intensive infrared radiation mostly triggers local thermal effect and even burns. Especially long-waved infrared radiation could cause high temperature and burns on the skin of the exposed body parts. As the skin can also conduct heat away, then the duration of the unfavourable effect depends on the intensity and exposure duration. For example, infrared radiation with power 10kW/m² triggers a pain reaction within five seconds; but 2kW/m² with about 50 seconds. If the exposure is long, then heat load on the body can be great, especially when the entire body is heated (e.g. working in front of an iron melting oven). This may result in the misbalanced thermal regulation system of the organism. The tolerance of such environments also depends on the employee’s personal tolerance level and environmental conditions (humidity, air movement speed). Without being engaged in physical labour, a human can tolerate 300W/m² during an 8-hour workday; whereas the same indicator is only 140 W/m² in the case of hard manual work.

Table. Organs Damage-Prone to Infrared Radiation

Prevention

Infrared radiation from commonly used lamps or most industrial devices does not harm the employees. In certain position that use special-purpose lamps, heaters and other sources of infrared radiation, the work process could damage the employees’ health.

The most effective protection against infrared radiation is the total screening of the radiation source. Attention must also be paid to heat bridges that could originate from the source. In most cases, the thermal screening of the radiation source brings the working environment into compliance with the marginal rates. In other cases, personal protective gear must be used. Thermally screening personal protective gear includes:

• mask or protective glasses,
• thermal uniform,
• thermal gloves, footwear and headwear.

In exceptional cases where the working conditions do not enable to apply the previous protective measures, administrative means must be used to protect the employees. For example, access can be limited to very hot areas of the working environment. It is also possible to decrease the input power of the heat source for the period when employees must work in its’ vicinity. Also shortening the worktime, taking more breaks or working in shifts can reduce the exposure time of one employee. It must be noted that working in a hot environment triggers heat stress in humans, which requires a longer resting time for recovering.

When evaluating the biological effects of the infrared radiation, we must consider the wavelengths and intensity of the radiation source, and the employee’s time of exposure. Marginal rates mostly protect against the harmful effect on the retina and cornea, and against latent influence on the lense.

The employer is obliged to determine the sources of infrared radiation in the working environment. If they exist, the level of radiation must be evaluated or measured, if necessary, and measures applied to limit the radiation to marginal rates. Regular sources of lighting are not considered as hazard sources.

The employer must inform all employees about all hazard factors, demand the use of personal protective gear, and enable breaks for resting the eyes.

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