Safety

The operation of terrestrial microwave and satellite uplinks unfortunately brings both the operator and occasionally the public into contact with a number of potential hazards. So we need to examine the range of hazards and the measures that can be taken to minimize the risks. There is health and safety legislation in many countries covering these hazards, and in the United Kingdom, the primary safety agency is the Health and Safety Executive (HSE).

The most important consideration when operating any type of microwave link is safety – there is a saying in the business, ‘no story is worth a life’. To consider the impact on the operation it is necessary to identify the specific risks. As we are going to look at risks and hazards, let us remind ourselves of the definition of risk and hazard, as occasionally there is confusion in their usage.

A hazard is anything that can cause harm – for example, electricity is a hazard associated with electronic equipment. Risk is the chance, whether high or low, that somebody will be harmed by the hazard – for example, how much of a chance is there that someone will be electrocuted in either operating or being close to an SNG uplink. It is important that the hazards and risks are clearly identified for two reasons. First, a human injury or life may depend on the correct action being taken, and secondly, the owner and/or operator of the microwave equipment may be liable to prosecution for failing to identify the hazards and take suitable steps to minimize the risks.

Outline of hazards

There are a number of potential hazards encountered when operating microwave links – whether terrestrial or satellite:

Non-ionizing radiation

As we talked about earlier in the book, microwave radiation can be used to heat organic matter up – and the word ‘radiation’ usually instils people with fear.

One of the first lessons anyone has to learn when being involved with the use of microwave transmitters is the hazard of radiation – but it is non-ionizing radiation, which is significantly different to ionizing radiation. So to dispel some myths, let us be clear about the differences between ionizing and non-ionizing radiation.

Ionizing radiation is radiation emitted by X-rays, gamma rays, neutrons and alpha particles that has sufficient energy to knock electrons out of atoms and thus ionize them. When this radiation passes through the tissues of a living body, in amounts above a safe level, then there is sufficient energy to permanently alter cell structures and damage DNA. This in turn can have dramatic and potentially catastrophic effects on living tissue, including, of course, human beings. However, used in controlled doses, ionizing radiation is widely used as a medical diagnostic and treatment tool, and provided the doses are within acceptable limits and there are adequate precautions to minimize the risk, there is little to fear from such use.

This is not the type of radiation associated with microwave-transmitting equipment. Microwave-transmitting equipment – which of course includes terrestrial microwave links, Inmarsat satphones and SNG uplinks – emits nonionizing radiation. In the following discussion on non-ionizing radiation, the term microwave transmitter can be taken to include the whole range of link equipment we have talked about.

The definition of non-ionizing radiation is electromagnetic radiation, which encompasses the spectrum of ultraviolet radiation, light, infrared radiation and RF radiation (including radio waves and microwaves). This is of much lower energy than ionizing radiation and therefore is unable to knock electrons out of atoms. When this type of radiation passes through the tissues of the body it does not have sufficient energy to ionize biologically important atoms, and therefore to alter cell structures or damage DNA. However, it does have thermal effects, and frequencies in the range 30–300 MHz have the greatest effect as the human body can more easily absorb them. At frequencies above this range, the body absorption is less, but still may be significant if the power levels are high enough.

Thermal effects are considered the primary health risk of non-ionizing radiation. The absorption of RF energy varies with frequency. Microwave frequencies produce a skin effect – you can literally sense your skin starting to feel warm if you are exposed to high power levels at microwave frequencies – but the real damage is happening deep inside your body. After all, as we said earlier, this is the principle on which microwave ovens operate, and you can cook human tissue just as easily with this type of power as animal tissue. While the terrestrial microwave links we have looked at can work very near to the same frequency as microwave ovens, why is there a problem with satellite uplinks operating at 14 GHz? Well, even the high levels of energy given off at this frequency could potentially cause some heating effects in the human body under the right conditions – standing directly in front of the antenna being the most obvious.

RF radiation may penetrate the body and be absorbed in deep body organs without the skin effect, which can warn an individual of danger. This is called deep burning, and there are certain parts of the human body that are particularly sensitive to these deep heating effects – the eyes, and additionally in males, the testicles. Therefore, power levels around microwave-transmitting equipment need to be kept below a certain level to minimize the risk to people.

Preferably, people need to be kept away from the most dangerous parts of this equipment, especially the antenna, which is designed to focus all this energy in a particular direction.