Action TU1208

Civil Engineering Applications of Ground Penetrating Radar

COST Success Story

Safety issues in Ground-Penetrating Radar and near-surface geophysical prospecting

Safety of people and equipment is a rarely considered issue in Ground-Penetrating Radar (GPR) and, more in general, Near-Surface Geophysical (NSG) prospecting. To the best of our knowledge, precise protocols for safety do exist with regard to specific geophysical works but they are, as a matter of fact, mostly related to “deep” geophysical applications [1].

As a general rule, “deep” prospecting usually presents more severe safety issues with respect to near-surface prospecting. For example, in the case of oilfield research, the crew may spend months in hazardous environments and handle harmful chemical substances, heavy and risky machinery, explosive material, machetes and other dangerous objects: such situations seldom happen in near-surface prospecting. Nevertheless, NSG surveys present peculiar safety issues worth to be seriously considered and they involve specific hazard factors. Another important preliminary consideration is that, in NSG prospecting, the crew is usually constituted by a few people. In most cases, there is no hierarchical assignment of the roles to be played with regard to the safety of people and instruments, neither it is planned how to afford accidents. Moreover, a larger crew is customarily much better equipped than a smaller one: safety equipment is usually brought in the field, if ten or more people are present; On the contrary, often, when few people are involved in the prospecting, they do not even think about risk prevention and accident management and sometimes they do not even bring with them a first aid kit.

Recently, the COST (European COoperation in Science and Technology) Action TU1208 “Civil engineering applications of Ground Penetrating Radar” [2] composed the state-of-the-art and critically analyzed the available information, to produce an extensive report on safety issues in near-surface geophysics, with a special emphasis on GPR inspection. Members of the Action along with renowned experts not involved in the Action contributed to this work. Dedicated discussions took place during TU1208 meetings, insomuch comments and questions coming from delegates turned out to be very useful to refine and enrich the report. A physician offered his precious and active collaboration. Legal aspects were also considered: a past work carried out by the EuroGPR Association, with regard to international regulations governing the manufacturing and use of electromagnetic devices, was exploited under permission and properly updated. Finally, the report was published by the European Association of Geoscientists and Engineers [3] and it was presented in Vienna, Austria, during the 2016 European Geosciences Union General Assembly [4].

The aim of this paper is to present and discuss a selection of safety and health issues associated to GPR and NSG prospecting, with the twofold purpose to increase awareness about these topics and foster a wider discussion.

In Section II, general recommendations are given, along with a description of minimal safety equipment that should be brought in the field. Additional equipment should be available if specific needs related to chronicle pathology of a member of the crew are known. In Section III, safety issues related to challenging environmental conditions are dealt with. During a GPR survey, the members of the crew can be exposed to demanding environmental agents, such as very high or low temperature and humidity rates, rain, significant height over the sea level, strong acoustic noise, ultraviolet radiation, atmospheric pollutions or dusts, and presence of insects, venomous animals and detrimental plants. For each situation, specific risks have to be considered. In Section IV, issues related to specific GPR applications are described, as demining and borehole inspections. Section V is focused on the safety of the instruments. Sections VI deals with GPR radio emissions. Conclusions follow, in Section VII.

 

II.GENERAL RECOMMENDATIONS

Geophysical prospecting is both a manual and intellectual work. Involved people need to take adequately prepared before carrying out a survey, in order not to cause hazardous situations for themselves and other people in the crew. People involved in a measurement campaign should never be:

•Under the effect of alcohol or drugs;

•Ill or convalescent;

•Exhausted before starting the activity, for example for not having slept enough.

Any misunderstood sense of duty has to be avoided: if we are not in adequate physical conditions, we cannot contribute to the success of the experimental campaign; conversely, we can become a problem or a risk factor for our colleagues and ourselves.

With regard to chronicle pathologies, depending on the kind of prospecting and environmental conditions, people might or should not take part to the campaign. If a non-ordinary measurement campaign is scheduled, people with any chronicle pathology are advised to contact a physician and take part to that campaign at hand if and only if allowed by the physician. Such a case-dependent evaluation is, for example, advised for people affected by hypotension, hypertension, heart problems, diabetes, kidney insufficiency, allergies, HIV, and hepatitis. In these cases, it is also appropriate to inform the crew about these chronicle pathologies. This has the dual aim to recognize possible problems in the field (so to provide an adequate and prompt first medical aid) and prevent any hazardous behavior with regard to possible contagions. If a person needs particular precautions, he/she should adopt them, according with prescriptions received by his/her physician, and the crew should be informed. The minimal safety equipment of the crew (described later on) should be enhanced according to the possible needs of these people.

The crew should always get informed in advance about:

•How to reach the medical surgical device closest to the place of the measurement campaign;

•Emergency telephone numbers, to be called for medical and police aid;

In addition, for experimental campaigns carried out abroad, it is advised to have at disposal the phone number of the Consulate and of the Embassy of our home country. It is well advised to have an efficient satellite navigation system and a signboard written both in English and in the local language, to ask where is the closest medical surgical device.

The following recommendations are also important. All members of the crew should:

•Be informed about the weather forecast and climate in the area where measurements have to be done;

•Bring with them adequate clothes (meaning both the right kind of clothes and an adequate quantity of clothes), suitable for the foreseen weather conditions and time-lenght of the survey;

•Be carefully informed about any logistic situation related to the prospecting at least 10 days in advance, in order to have the time to be prepared with regard to all safety issues related to the prospecting at hand.

It is recommended that at least a member of the crew is trained for handling emergency situations and first medical aid. All members of the crew have to be informed about the location and content of the medicine chest, in order to be able to easily reach devices and/or medicines when needed.

The crew should be always equipped with a medicine chest containing at least the following objects:

•Sterile disposable gloves;

•Visor against squirts;

•1 L of povidone-iodine at 10%;

•Compresses of sterile gauze 10 cm  10 cm (10) and 18 cm  40 cm (2), in single envelopes;

•Disposable sterile coveralls (2);

•Sterile disposable tweezers for medication;

•A package with medium-size elastic mesh;

•A package of absorbent cotton;

•Two packages of adhesive plasters of various size;

•Two rolls of adhesive plaster 2.5 cm wide;

•Scissors;

•Two packages of dry ice, ready for use;

•Two disposable bags for medical garbage;

•A thermometer;

•A blood pressure monitor.

In Fig. 1, some of the listed items are shown. The medicine chest has to be in good condition: It should not be broken, cracked, or rusted. It should not be exposed to the sun and get wet. Medicines contained in it have to be not expired. The medical chest can be possibly integrated with further devices/medicines, depending on the specific needs that the prospection might impose. Some devices should be used only by people that have attended a first medical aid course.

 

Fig. 1 – Some of the advised medicine-chest items. A: Sterile disposable gloves; B: Visor; C: Sterile disposable coverall; D: Sterile disposable tweezers; E: Dry ice; F: Blood pressure monitor.

More information on the topics mentioned in this Section, suggestions for eye protection and handling of heavy objects, recommendations for pregnant women, and hygienic and alimentary precautions, are in Chapter 1 of [3].

 

III.CHALLENGING ENVIRONMENTAL SITUATIONS

During geophysical prospecting, the members of the crew can be exposed to high or low temperature, rain, height over the sea level, acoustic noise, ultraviolet radiation, atmospheric pollution or dusts, insects, venomous animals and detrimental plants. For each situation, specific cautions can be advised. Here, due to space limitations, we focus only on high temperature, low temperature and prospecting at heights. More details on the other mentioned situations, suggestions for prospecting in polluted environments, on lakes, and in potentially infective situations are given in [3].

With respect to prospecting in the presence of high temperature, this is an issue of high interest because in many cases GPR inspections are carried out during summer (for example, in archaeological sites [5]-[7]), when the soil is drier and the signal penetration is higher. In such situations, it is advised to start the work at dawn and stop at lunch time, possibly devoting the afternoon to data processing activities and avoiding further measurements under the sun. People performing measurements shall wear a hat, or a cap with a visor. A portable fridge is advised, but beverages should be at a temperature not colder than 8°C, without gas and never alcoholic. Moreover, the following suggestions are given:

•To drink frequently limited quantities of water or beverage (avoiding to ingest more than 1 L in a unique booze-up);

•To wear light clothes, particularly white and made of cotton or linen, with long trousers and thick shoes with socks (in order to be protected against snakes, spiders, scorpions, or pricky grass);

•To do an adequate number of short breaks;

•To avoid abundant meals, caffeine and excessive quantities of sugar;

•To avoid touching with bare hands any metallic object that has been under the sun;

•To avoid wearing metallic objects such as earrings, necklaces, and writs watches; sometimes even the frames of sunglasses can become very hot;

•It is better to have at disposal some shadow; if a naturally shady area is not available, it should be created by means of an umbrella or a tent.

It is important to get informed in advance about the behaviour to adopt in case of sunstrokes or burns. Also, it is important to know in advance where is the closest medical presidium, especially when working far from home.

The case of low temperature is also important: polar ices and glaciers are of interest for GPR researchers, who can study the stratification and thickness of the ice, which reveals important aspects of the geological history of our planet [9]. In such cases, it is advised to have at least one person who is expert of the climatic conditions that the crew is going to meet. In order to mitigate the risks of pathologies as frostbites and (above all) hypothermia, it is advised to:

•Wear layered clothes and, if possible, propylene clothes adherent to the skin because this will limit heat dispersion, particularly in case of windy areas;

•Keep the clothes dry (humidity increases heat dispersion);

•Wear a cap to adequately protect the head and ears from frostbites, gloves to protect the hands, and impermeable boots to protect the feet;

•Cover, if needed, the face and eyes;

•Exploit the facilities before going in the field.

It is extremely important to get informed in advance about first medical aid to be given to a person in case of frostbite and hypothermia, as well as to know where is the closest medical presidium.

Prospecting at heights is of great interest because ancient archaeological sites [10] or modern mountain resorts might be placed at 3000 m or more over the sea level. In these cases, beyond possible issues due to the low temperature, there are serious risks linked to hypoxemia, namely the decreased percentage of oxygen contained in the air. In particular, at the height of 3000 m the oxygen is on average 31% of that at the sea level, and at higher levels this percentage decreases further on. The human body is in most cases able to automatically adjust to these conditions, but a time for naturalization should be always guaranteed before starting the work. The main advices are:

•To perform a gradual ascent, sleeping at least one night at about 3000 m and also one night at the level of the site before beginning the work;

•An ascent not faster than 500 m per day beyond the level of 3000 m is suggested, and one day of rest before starting the work after the ascent is completed.

Fig.2 shows a schematic example.

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.

 

 

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For information concerning the COST Action TU1208, please take contact with the Chair of the Action, Dr. Lara Pajewski - This website is supported by COST, European COoperation in Science and Technology - COST is supported by the EU RTD Framework Programme Horizon2020.

TU1208 Members are deeply grateful to COST for funding and supporting the COST Action TU1208.