Safety of electromagnetic factors for the workplace equipped with personal computers in residential premises

Objectives. The aim of this paper is to analyze the electromagnetic safety of 50Hz industrial frequency electrical networks in residential buildings when using workplaces equipped with personal computers (PCs), as well as to develop recommendations on reducing the impact of levels of industrial frequency electromagnetic fields on human health in residential premises. Methods. Electromagnetic fields in residential premises with the single-phase TN mode industrial frequency power supply system regulated by the Rules of Electrical Installations Design were measured and calculated in accordance with Russian and international legislative documents. Results. It was established that electromagnetic fields induced by TN networks in workplaces equipped with PCs might increase significantly and even exceed the maximum permissible level of 25 V/m and 0.25 μT recommended by Sanitary and Epidemiological Standards. Residential buildings are not subject to the requirements of the Energy Supervision services; therefore, any unprofessional modification of electrical networks in residential premises, including the use of unapproved extension cords, may result in sparking, high-frequency harmonics, and, in turn, conditions which impact human health, as well as electric injures, fires, and gas explosions. Conclusions. It has been shown that IT (TT) mode symmetrical two-phase electrical networks may function efficiently for decades without accidents and effects of industrial frequency electromagnetic field on humans, as they are used in medical institutions, defense enterprises, and state institutions. Thus, legislative transition to installing IT (TT) systems in residential buildings, replacement of existing TN power supply systems with IT (TT) system, and legislative strengthening of requirements for household protection and commutation devices, may also be required to reduce man-made disaster risks in residential buildings.


INTRODUCTION
In practice, even one workplace equipped with PC (WP PC) (sometimes more than 8 hours and during night-time) in residential premise may give rise to problems threatening the life and health of employees (students), as well as other residents. Some households have three or more WP PCs. In addition to the negative stress impact of domestic and family worries, many other cases of extreme fatigue, tiredness, and decreased performance at the end of the working day have been identified in results of private surveys and remote employee complaints, when compared with using WP PCs located in offices.
According to Order No. 33n of January 24, 2014 of the Ministry of Labor and Social Protection of the Russian Federation 1 , a special assessment of working conditions in respect to WP PCs was nearly canceled. The new version of the Sanitary and Epidemiological Norms (SanPiN) 2 approved by the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing (Rospotrebnadzor) entered into force. This was without any argumentation in terms of sanitary impacts, or discussions with experts on Internet. This also excluded Swedish electromagnetic compatibility (EMC) requirements for WP PCs (SanPiN 2.2.4.3359-16 3 , paragraph 7.2.7, Table 1), while canceling SanPiN itself.
Remote WP PCs are located usually in residential premises often unadapted for this purpose (power supply, Internet connection, office equipment, and communication). While the employer is responsible for safety in office WP PCs, ensuring responsibility for the fire, electrical, and electromagnetic safety of the remote workplace does not fall under supervision of the Russian Ministry of Emergency Situations, Energy, and Sanitation Departments.
All departmental documents related to ensuring safe conditions in housing and communal services (HCS) 1 Order of the Ministry of Labor and Social Protection of the Russian Federation No. 33n of January 24, 2014 on the endorsement of the Method of special assessment of working conditions, Classifier of adverse and/or hazardous production factors, form of report of the carried out special assessment of working conditions and its filling instruction. Amended on April 27, 2020 (in Russ.). 2 4 . This states that "the management of an apartment building should ensure the favorable and safe living conditions for citizens". It also proposes a General Declaration. Thus, users themselves are now responsible for monitoring living conditions in premises and safety of WP PCs, in order to preserve their health as well as the health of other residents.
Remaining indoors for too long may become uncomfortable and dangerous in conditions of weakened geomagnetic field (GMF) and distorted geoelectric field (GEF), as well as in conditions of increased man-made electromagnetic fields (EMF). Residents today may not even realize the reduced natural EMF and increased man-made EMF in their homes, WP PCs, bedrooms, and kitchens. The Ministry of Emergency Situations, health and sanitary information, and mass media cannot encourage residents to monitor EMF conditions in their premises independently, despite the simplicity of such monitoring comparable with the use of a smartphone [1][2][3][4][5][6][7].
After monitoring complaints from house residents for several years concerning dangerous and uncomfortable living conditions has revealed that up to 60% of all cases are caused by electrical networks with TN earth system 5 with solidly grounded neutral (French: Terre -Neuter) in accordance with the Rules of Electrical Installations Design (PUE) 6 for residential premises (PUE, paragraph 7.1.13) and public buildings (PUE, paragraph 7.2.9) [1]. Left over many years, unattended household TN electrical networks may result occasionally in sparking and short circuits (SC). This may result in multiple accidents, such as explosions, fires, and electrical injuries causing destruction of buildings and loss of life.
In contrast to international standards on electrical safety, Russian electrical networks are equipped with circuit breakers (CBs) and residual current devices (RCDs) with reduced reliability requirements. This exacerbates the risks of explosion, fire, and electrical hazards in buildings with TN mode single-phase power supply. Two-phase symmetrical IT (TT) networks 7 with safety criteria much higher than those of TN networks should be used in residential and public buildings 4 Federal Law on Amendments to Housing Code of Russian Federation No. 59-FZ, dated April 3, 2018 (in Russ.). 5 Electrical network with solidly grounded neutral in accordance with PUE, paragraph 1.7.3 (in Russ.). 6 10 for sleeping areas, and the World Health Organization (WHO) principles [1,2].
The primary aim of the paper is to establish the following: the causes of TN network operational hazards in residential premises; the safety and efficiency of IT networks; and the need for selfmonitoring of recommended IF EMF criteria for WP PCs.
Uncomfortable EMF conditions in premises today depend not only on the construction quality and external environment, but also on the residents and their qualifications, as well as selfmonitoring system and the capability to normalize these conditions. Equipping WP PC should be accompanied with continuous monitoring of IF EMF and other factors (

CAUSES OF UNSUITABLE CONDITIONS FOR REMOTE WP PCS IN RESIDENTIAL PREMISES
Millions of WP PCs located in offices, classrooms, and factories are subject to EMF requirements and standards (Table 1) and these should also be extended to remote users in residential premises. These requirements were first set out in the MPR 1990 standard (Sweden) 12   and have been used worldwide as MPL for WP PCs equipped with electronic tube displays. Since 2000, WP PCs have been equipped with new and safer LCD displays. At the same time, secondary switched power supplies (SMPS), such as adapters, electric appliances, light-emissive device, and etc., distorting IF currents and voltages of 50 Hz in TN network have come into broader use. This induces a parasitic EF and MF spectrum on frequency bands almost equal to the MPR 1990 standard in the premises. Figure 1 shows typical voltage and current waveform distortions in a three-phase 50 Hz electrical network of a residential building.  Current distortions may be caused mainly by asymmetry of consumer phase loads in the building network and nonlinear current loads in phases. Each current (voltage) harmonic of the TN network phase induces MF (EF) in living spaces and form a wideband spectrum with energy possibly greater than that of the 1st harmonics. The Swedish standard requirements for IF EMF (Table 1) [11]. About forty transformer substations built-in and attached to building in Moscow, Moscow region, and Samara are equipped with shields (thin-walled steel sheets with a grid between them). They convert elliptical IF RMF of the source to the quasi-linear component of IF MF (less dangerous), according to the method described in [11]. 5. Today, foreign environmental organizations recommend (oblige) builders to comply with rigid SBM-2015 standard (8th edition) for advisable 50 Hz IF background in residential premises. This should be no more than 5 V/m and 0.1 μT, motivated by WHO warning provisions for residents' exposure to household EMF and other harmful factors. The SBM-2015standard of building biology methods is used as a guide for professionals and independent testing of residential buildings worldwide, including Europe, Israel, USA, Canada, Australia, and New Zealand [12]. 6. In the European Union, the transition to standards for IF MF ranging from 0.2 to 0.4 μT is considered as a promising target for coming years. The decisions at the WHO level are expected to be made in 2022-2024 [13].

CAUSES OF DANGEROUS CONDITIONS IN RESIDENTIAL PREMISES DUE TO TN POWER SUPPLY SYSTEMS
The mass media often cite TN electrical networks among the causes and conditions of accidents occurring in residential and public buildings, resulting in injury and death. According to the degree of potential danger to the quality of life (QOL) and health of the residents, costs of treating victims, as well as damage to work results along with costs of future restoration and repair, these accidents should be classified as extremely dangerous for their resulting frequently in catastrophic damage.
Two-wire TN-C network 16 , among other TN modes, may most frequently cause domestic gas explosions, fires, electrical injuries, and parasitic inductions of 50 Hz IF fields in premises. These networks may be found in building walls towards outlets and light sources (due to mistakes Yuri G. Ryabov, Nikolai M. Legkiy, Geliy V. Lomaev Safety of electromagnetic factors for the workplace equipped with personal computers in residential premises of constructors) as well as in cases of contact failures in the third PE 17 wire and non-standard extension cords. The two-wire network may be detected by the increased EF induction. A short circuit in a TN-C network can result in fire. When a PEN 18 neutral wire is broken or burnt, the voltage at the L (phase wire) terminals may increase up to 0.4 kV. This voltage is dangerous to people and may appear on all metal parts connected to the PEN wire. According to PUE, paragraph 7.1.78, plugged in and unprotected domestic appliances, adapters, and light sources may be burnt. In Russia, using the TN-C networks and two-wire extension cords are currently prohibited by fire authorities.
Despite the use of upgraded TN-S 19 and TN-C-S 20 power supply systems in residential buildings, according to PUE, paragraph 7.1.13, gas explosions, fires, and electric injuries may also occur from time to time in recently constructed buildings. In Russia, about 30-50% of annual household gas explosions are caused by sparking in TN electrical network. This usually happens when commutating light switches, socket contacts, electrical appliances, inter alia. Spark intensity may increase due to the additional discharge energy of the distributed capacitance С D = 110...130 pF/m from the "earth" wire. It is therefore not recommended to use TN networks in areas of possible concentrations of dust and air explosive mixtures. Sparking may be dangerous for electronic devices in the event of earth fault (contact loss) and other factors.
Today, protection against electrical hazards and short circuits in TN-S and TN-C-S building networks depends on the CB and RCD response speed. Fires and electrical hazards may often occur due to the low contact reliability of electromechanical devices and long response time (up to 5 seconds, according to PUE, paragraph 1.7.79) in residential and public building networks. According to the expert opinion on the cause of the fire in the Zimnyaya Vishnya shopping mall: "The fire started in the LED light fixture which was inundated by melt water from the roof. The circuit breakers intended for switching off the lighting device and then the power supply failed to actuate 21 ." Electric shock and commutation sparking occurring in TN building networks is always added to the discharge energy of the distributed capacity С D . This causes degradation (erosion) of contacts. In TN system, the presence of electromechanical CB and RCD does not mean full protection against short circuits and electrical hazards. Protection devices with a cut-off time two orders of magnitude less than that established in PUE [1,2] are required.

CAUSES OF UNSUITABLE CONDITIONS FOR REMOTE WP PCS DUE TO IF EMF
Complaints from domestic residents with regard to unsuitable living conditions are often due to the 50 Hz IF EF and MF induction. These frequently do not exceed the MPL established by SanPiN 2.1.2.2810-10 ( Table 1). Voltages in TN electrical networks running in walls, ceiling, and floor may actuate steel rebars and wall grids (not earthed) and induce parasitic (secondary) EF with intensity up to 25 V/m (MPL for WP PCs) in premises at 0.4-1.0 m from walls. Network extension cords running under the user's feet, especially two-cable ones (used at more than 50% of WP PCs in Russia), appliance and adapter cords, and table (wall) lamps may induce EF in the surrounding space. This excites secondary EF in metal objects located close to the user, such as tabletop, chair, armchair, support, spring mattress, inter alia.
In the case of locating WP PCs, conditions may become unsuitable even when all the cords of IT devices and adapters are merely plugged into the sockets and extension cords of the TN power supply (~220V). IF EMF intensity at a distance of 0.1 m from cords and three-wire extensions may reach 100-125 V/m. This is 4-5 times more than MPL for WP PCs (25 V/m) established by SanPiN 2.2.4.3359-16 (Table 1) [1,2].
The need to multiply the TN network (plugging appliance cords, adapters, and etc. in) by means of extension cords, as well as increasing the number of current commutations when equipping and operating WP PCs in residential premises, may increase the risk of explosion, fire, electrical sparking, and unsuitable conditions, which are monitored and protected by nobody. In TN network, dangerous conditions often arise when the contacts of the working and protective earth wires are broken or lost even before entering the premises, apartment, distribution board, inter alia. Geliy V. Lomaev Safety of electromagnetic factors for the workplace equipped with personal computers in residential premises Russian Technological Journal. 2022;10(2): [14][15][16][17][18][19][20][21][22][23][24][25][26][27] There have been a number of instances, when a baby's bed located close to and exposed to EF voltage of ~(80-100) V/m emitted by device cords (heater, ionizer, baby monitor, etc.) has been relocated to another place, thus normalizing EF conditions to less than 10 V/m, resulting in the disappearance of chronic diseases [2].

SAFE POWER SUPPLY SYSTEMS REQUIRED FOR REMOTE WP PCS
There is no statistical data regarding accidents and excesses of IF EF and MF values in healthcare facilities, defense enterprises, and banks using potentially safe two-phase symmetrical IT (TT) networks, manufactured pursuant to GOST R 50571.28-2006 (IEC 60364-7-710: 2002) 22 (PUE, Fig. 1.7.4).
The results of inspections and tests performed in buildings in accordance with RD 153-34.0-15.501-00 23 and RD 153-34.0-15. 502-2002 24 show that the IT electrical network efficiency is higher than that of the TN, in terms of the following values: • Explosion and fire risks, up to 5 times; • Electrical safety, more than 10 times; • Electromagnetic safety, at least 10 times; • Pulse (lightning) resistance, by 1.5-3 times (civil defense); • Energy saving (current drain reduction), up to 5%; • Resource conservation including network isolation and commutation device contacts as well as reduction in the electro corrosion rate of building engineering systems, by 2-3 times, etc. Contact with any wire of the IT network is safe, and secondary inductions from ungrounded objects do not occur. IF EF inductions from network extensions decrease. Conventional CB and RCD protection devices, as well as electromagnetic shielding would be more effective for these networks. When commutating current loads and short circuits, the spark energy is several times lower due to the absence of capacity discharge С D . This energy may be compensated by multidirectional bias currents from each wire of the network. The cases of domestic gas explosions are unknown yet [1][2][3].
In the case of a single ground fault in one of the IT network conductors, even though the circuit breakers have not tripped, the IT network may be converted provisionally into TN-C network until the fault is eliminated. In the case of a ground fault in the second conductor, the emergency network should be switched off. Voltage to earth from each IT network wire is about 110 V. The EF intensity is 1-2 V/m, while the MF one is about 10 nT at 0.1 m from the wires [2].
Today, the service entrance for the threephase TN network (~220V) in an apartment or detached house may have been equipped by certain enterprising people with an isolation transformer (PUE, paragraph 1.7.85) up to 15.0 kW. This transmits an already potentially safe electrical IT network or TT network earthed via a middle point (PUE, Fig. 1.7.5) to WP PCs in residential premises through the same wires. In order to protect a detached house from EF and MF parasitic inductions, as well as from parasitic interferences in the electrical network which may occur during thunderstorm, short-circuit, and wire breakage, an isolation transformer with separate windings (or with the earthed shield) and overvoltage suppressors may be installed on the property line [2].
In order to protect remote WP PCs from IF EF of TN network (~220 V), neutralizers may be used for decoupling ~220 V from ground (earth), suppressing EF in the range from 5 Hz to 400 kHz, with a noise level up to 20 dB, such as Cyclone 650 with 4 sockets (produced by the Cyclone-Test 25 ). are reliably fulfilled, provided that an IT network (or TT network) is used and there is no induction or radiation from external sources which exceed the criteria, specified in Table 2.

JUSTIFICATION FOR EMF RECOMMENDED CRITERIA (TABLE 2) FOR WP PCS
An example of parasitic EF (23 V/m) induced by a cord plugged into the network adapter (~220 V) at ~0.5 m (wooden ruler) close to IF EF MPL for WP PC (Table 1) is shown in Fig. 2  An example of a household WP PC is shown in Fig. 3 [14]. Clearly the PC power cords and LCD display and laptop cables are hanging down from the metal tabletop and are plugged into extension outlet sockets. When a TN network is used, the EF and MF secondary induction (ranging from 5 Hz to 2 kHz) from the tabletop and cords near the user's knees may be up to 80 V/m and 0.6 μT instead of MPL amounting to 25 V/m and 0.25 μT. 26 Fig. 3. Household WP PC [14] Other factors of discomfort (Fig. 3) may be: IF MF, EF, and RMF induction from power cables behind the wall; inductions of the opposite directions of GEF or ESF vectors of the armchair, foot support and floor laminate; reduction of GMF due to wall metal structures; SHF radiation from nearby devices, such as Wi-Fi devices, laptop board, and cell phones (especially, using GSM standard). When an IT network is used, IF EF and MF values would automatically meet the conditions specified in Table 2.
Remote WP PCs should comply with EMF values and criteria (  (Table 1): nervous system; cardiovascular system; endocrine system; immune system; digestive system; and the reproductive system [10]. When WP PC is exposed to the range of EMF factors, the intensity of each factor should be reduced to protect against the devastating health impact on users. 3. The recommended criteria for factors 4 ( Table 2) are more severe than EMF MPL (Table 1). Here, the following aspects have been considered: use of safe IT (TT) network in buildings and premises; exposure to the reduced and distorted GMF factors in premises practical achievability of the criteria indicated in Table 2; MPL reduction of other physical factors in the event of 24 hours, instead of 8 hours, in the office.

CONCLUSIONS
1. Based on the above results, the following priority activities should be implemented in residential buildings and premises as legislation: • Replacement of TN power supply system with IT (TT); • Use of a more reliable commutation and protection systems; • Implementation of a system for monitoring physical factor conditions by residents and users of household WP PCs who use modern mobile devices.
2. The following requirements should be conveyed to the Government of the Russian Federation, regional authorities, population, investors, constructors, and power engineers: use of ungrounded IT power supply system in designing new residential and public buildings, rebuilding, and overhauling; recommendation for the safe and comfortable EMF factor conditions as shown in Table 2