Fig. 2 – Suggested scheme for ascent, rest and work times for a prospecting at 4000 m a.s.l..

People affected by pathologies as for example respiration insufficiency and myocardial ischemia, people who have had a heart attack, and people with anemia of the drepanocytosis kind, are strongly advised to consult a physician before leaving for prospecting at heights. Some discomfort is acceptable and natural at heights, but in case of serious problems (the most severe ones are the cerebral edema and the pulmonary edema) the person should be immediately brought at lower heights and then at the closest medical presidium. It is important to get informed in advance about first medical aid techniques and location of the closest medical presidium.

IV.RISKS ASSOCIATED TO SPECIFIC APPLICATIONS

Beyond risk factors related to challenging environmental conditions, it has to be considered that specific applications can involve specific factors of danger, or else they can make general factors of risk particularly important and worth considering. In [3], recommendations are given for GPR demining, bridge and road surveying, sedimentological investigations, archaeological prospecting, mining and tunneling, forensic applications and borehole inspections. Also, few suggestions are given for the safe use of further geophysical techniques beyond GPR, as e.g. the induced polarization. Here, we focus on demining, mining, tunneling and inspections carried out by using borehole radar.

Demining is the most dangerous application in NSG, only people authorised and specifically trained can do it. In most cases, the deminer not only knows how to find the mines but also how to deactivate them or how to make them explode in a safe way [10]. If one wants to undertake such a job, he/she has to apply for an authorisation. Relevant information can be requested to the Geneva International Centre for Humanitarian Demining. If the application is accepted, the authority in charge, or a specialized organisation, will arrange support including personal protective equipment, evacuation plans, emergency transport, medical assistance and a training course.

With regard to mining and tunneling applications, the main sources of danger are dust and methane. These are mainly related to coal mining, but not only. In particular, when operating with radio or radar equipment, there is a possibility that radio signals trigger electronic blasting caps or interfere with machine interdiction controls. The “mine dust” is the result of mining machines cutting the rocks between coal and sandstone. This affects coal miners due to chronic inhalation of micro-fine dust particles. Heavy metals or radioactive material may also be present, which may require further precautions. With regard to the methane, the main problem is the fact that metal objects or old well casings might create a spark when we hit them with mining equipment. Therefore, a safety region of 15 m from known objects potentially dangerous in this sense is a standard practice. Another ignition source is the boundary layer of the coal seam. In particular, when the coal-cutting drum bits cut through the coal seam and into the boundary-sandstone sedimentary rock, sparks can cause methane ignition occur. Therefore, 30 cm of roof and floor coal is typically left by mining operations. Suitable certifications exist for the electronics exploited within the mine, and it is advised to make use only of them. In any case, it is never advised to begin a prospecting in a mine without a preliminary briefing with expert people.

With respect to borehole applications [11], safety issues exist related to the weight of the radar probe, which can be from 1 to 300 kg, and its length, which can be from 1 to several meters. A scaffold and a crane may be required and scaffolds may collapse accidentally if not installed securely. Moreover, the human operator may fall when he/she loads or unloads equipment, such as pulleys, on the top of the scaffold. A second scaffold with a handrail and a work floor must be set in order to allow the human operator working safely. A helmet should be kept when performing these activities.

In borehole applications, the radiated electromagnetic power can be higher than in conventional GPR systems. In particular, the voltage at the feeding point can reach 800 V and the effective radiated power, with a continuous-wave system, can reach 20 dBm. The radar antennas are not shielded (they would become too large and heavy). Therefore, the electromagnetic waves can be transmitted from the subsurface to the air and can interfere (especially in urban areas) with medical instruments and communication systems. Long-term exposure to high-power electromagnetic waves may affect the operator's health. Hence, the generator should be never turned on when the antennas are not in the holes. Sometimes a borehole prospecting is performed in old mines, in a deep gallery. In such cases, the operator should be aware of the local conditions in the mine and follow the mine manager's instructions, in order to understand in advance whether there is a danger of rock slide.  The ventilation system should be checked. A helmet should be worn.

V.SAFETY OF EQUIPMENT

Several precautions are suggested in [3], to make a correct use of the instruments used during the prospecting. First of all, their mounting should follow the indications reported in the manuals. After usage, the instruments should be arranged back in their bags and properly preserved. If the laptop where data are stored is not inserted or cached into a rigid structure, than it should be adequately fastened, in order to avoid its fall during the use. The bags for the instruments should not be forgotten open. The batteries should be never damaged, because they usually contain toxic and polluting substances. The instruments should be never used beyond the allowed range of temperature, which is usually specified in the data sheets.

With regard to the transportation of the instruments, we might do this operation ourselves or exploit a courier. In the latter case, it is advised to assign this task to a personally known and trusted expedition company. It is better to avoid call centers: in fact, if some problems occur for any reasons, telephone operators usually are not able to solve them directly. Consequently, things can become more and more difficult with a possible economical damage. It is advised to follow every day the status of the expedition: Problems can occur all the times, and if you do not check, you might be contacted after several days. If the instruments have to be sent abroad, an ATA Carnet may be needed. This is an international customs and temporary export-import document; it is used to avoid customs duties in 85 Countries, on merchandise that will be re-exported within 12 months.  The ATA Carnet is also known as Merchandise Passport or Passport for Goods, depending on the Country. You should get informed and request the ATA Carnet at least one month before sending the instrument or leaving. Usually, the ATA Carnet has a validity of one year, then it has to be given back to the authority that granted it. During this year, four stamps are needed any time the equipment goes abroad: A stamp from the customs of your country (for temporary exportation), a stamp from the customs of the country where you have to perform the prospecting (for temporary importation), a stamp from the customs of the country where you have performed the prospecting before coming back home (for re-exportation), and finally a stamp from the customs of your country (for re-importation). Couriers should know everything about this, but in many cases they do not. So, it is warmly advised to be prudent and careful.

If one brings the instruments with himself/herself, safety while driving has to be considered. In many cases one does not use his/her own car, but rather a car belonging to his/her company or institution. A check is needed every time a long trip has to be done. When driving abroad, extra attention is needed due to the fact that signs might be different and written in another language. Moreover, one might pass through countries where driving goes from the right-hand side to the left-hand side, or vice versa. Examples of close countries with different driving conventions are China (right-hand) and India (left-hand); Venezuela (right-hand) and Guyana (left-hand); Italy (right-hand) and Malta (left-hand); Turkey (right-hand) and Cyprus (left-hand). All documents of the car, as well as your own driving license, have to be not expired. Snow chains might be needed, even if the country to be reached is not cold, because some mountains might be crossed during the trip.

VI.GPR RADIO EMISSIONS

GPR is a device that radiates non-ionising electromagnetic waves. Hence, its use requires caution related to the absorption of electromagnetic power by the human body. To the best of our knowledge, there is no comprehensive study specifically related to the radio absorption of energy radiated from GPR systems and its possible short- and long-term effects.

The power density radiated by GPR systems is customarily several orders of magnitude lower than the well-known international radio frequency limit of 1 mW/cm2. Usually, power levels radiated by GPR systems are of the order of a few mW as peak power and on the order of a few µW as average power (with the exception of borehole GPR systems, which radiate with antennas inserted under the air–soil interface).

The levels of electromagnetic fields impinging on the operator depend on the system (in particular they depend on whether the GPR is pulsed or stepped frequency) and on the surrounding environment. The energy is essentially radiated in a broadcast direction (again, with the exception of the borehole systems), i.e., away from the human operator, which is both a technical need and a legal requirement in Europe and North America. The human operator lies “behind” the source, where the levels of emitted fields are much smaller than those recordable in front of the antenna (i.e., underground, or inside the inspected structure). This holds particularly if the system is equipped with shielded antennas, which happens virtually all the times except for prospecting at low frequency (below 100 MHz) and in borehole applications. Therefore, although quantitative and exhaustive studies on the human absorption of electromagnetic power emitted by GPR systems do not exist, there is no reason to be excessively worried. Some measurements were carried out in the framework of COST Action TU1208 [12], which confirm this claim. There also are indirect proofs of this claim. For example, external electromagnetic interference is often gathered by GPR systems: Skilled users are able to recognize tracks of such interference in the data and, when the interference is caused by narrow-band signals, they know how to erase or mitigate it through a suitable filtering. However, while interference of other electromagnetic systems on the GPR image is a well-known occurrence, we have no notice about televisions, radios, mobile phones, computers, or any other devices perceivably disturbed by GPR prospecting performed nearby.

GPR systems operate from 10 MHz up to 5 GHz, with about a decade of bandwidth within that range, thus belonging to the most extreme class of ultra-wideband (UWB) radars. The basic steps that need to be carried out in order to evaluate GPR electromagnetic emissions and compare them to the limits reported in jurisdictions, are presented in [13]: in that paper, a procedure is proposed to translate UWB GPR data into the regulatory parameters.

Compatibility studies have been performed by the Federal Communications Commission (FCC) and the European Conference of Postal and Telecommunications Administrations (CEPT). The FCC stated that: “taking into account expected mitigation factors like the very low density and activity factor, the deactivation mechanism (e.g., switch off the equipment when normal use is interrupted), the frequency dependency of wall and ground attenuation, then the risk of interference into any of the radio communication services is assumed to be low. It should be noted that GPR/WPR systems have operated for many years under interim arrangements, and no cases of harmful interference have been reported, although some radio applications have not yet been deployed.”

This does not mean that no caution has to be taken. In particular, the main suggestion is to avoid pointing a radiating GPR antenna versus any person. Moreover, the crew members who are not operating the radar should be as distant as possible. It is well advised to alternate the human operator driving the GPR periodically during the prospecting, particularly if many hours for several consecutive days have to be spent in the field. Note that the laptop on which we see the data in real time during the prospecting emits microwave radiation when it is switched on (as all computers): The power density emitted by the laptop and impinging on the human operator is in general higher than the homologous quantity referred to the antennas of the GPR system. Notwithstanding, people that have or have had a cancer are advised to consult a physician with regard to their possibility to take part to a prospecting and about what are they allowed to do in the field.

Beyond these practical cautions, it is advised to check that any due guarantee from the manufacturers of the instruments is documented. In fact, GPR instruments have to respect specific regulations with regard to the emitted power, as explained in [3]. Note that the fact that GPR systems are (and have to be) certified, implies that the users should never modify them (for example, with the purpose of improving their performance) as this may drive the system out of the regulation limits, damage it, and make it harmful for the users.