Article
Ignition of welding arc and UV actinic hazard
evaluation
Andrzej Rybczyński 1,∗ , Agnieszka Wolska 2,
Tomasz Pfeifer 5
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, Mariusz Wisełka 3 , Jolanta Matusiak 4 and
GL OPTIC Polska sp. z o.o sp. k.; ul. Poznańska 75,62-040 Puszczykowo, Poland;
andrzej.rybczynski@gloptic.com
The Department of Safety Engineering; Laboratory of Optical Radiation; Central Institute for Labor
Protection - National Research Institute; ul. Czerniakowska 16 00-701 Warsaw, Poland; agwol@ciop.pl
The Department of Safety Engineering; Laboratory of Optical Radiation; Central Institute for Labor
Protection - National Research Institute; ul. Czerniakowska 16 00-701 Warsaw, Poland; marwi@ciop.pl
Welding Technologies Department ; Instytut Spawalnictwa; ul. Błogosławionego Czesława 16-18 44-100
Gliwice, Poland; jolanta.matusiak@is.gliwice.pl
Department of Resistance and Friction Welding; Adhesive Bonding and Environmental Engineering; Instytut
Spawalnictwa; ul. Błogosławionego Czesława 16-18 44-100 Gliwice, Poland; Tomasz.Pfeifer@is.gliwice.pl
Correspondence: andrzej.rybczynski@gloptic.com; Tel.: +48-607-233-080
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Abstract: Welding arcs emit strong UV radiation which could pose serious health risks for skin and
eyes. According to European Directive 2006/25/EC, ultraviolet (UV) hazard evaluation has to be
performed in working environment. The measurement of welding arc ignition radiation is a difficult
task. This article shows the effort to determine actinic radiant exposure levels during welding arc
ignition in controlled environment of a welding laboratory. New proposition of UV actinic hazard
evaluation from welding arc ignition radiation using a CCD spectroradiometer combined with
photometer was presented. The hazard of UV emitted in pulsed metal active gas welding (MAG-P)
of construction steel was shown. Duration of ignition peak was in range 9 ms – 15 ms. The actinic
radiant exposure during arc ignition over aversion response time was in the range 0.26 – 1.12 W/m2 .
The daily exposure time can easily exceed the permissible exposure time obtained in our study, i.e 7 s
- 29 s. It means that UV radiation form MAG-P arc welding is hazardous for the eyes and skin not
only for welders but also for workers in the vicinity of welding arc. Presented measurement method
enables determination of radiant exposure of arc ignition radiation.
Keywords: welding arc ignition; UV radiation; actinic hazard evaluation; CCD spectroradiometer;
photodiode/ flicker meter; measurement method of arc ignition radiation
1. Introduction
Welding is an important technological process for materials joining by a suitable application of
heat and/or pressure. Arc welding is a process in which heating of the metal’s surface to the point of
melting is accomplished by an electric arc. Burning arc between electrode and metal piece produces
a very high temperature which causes melting of the joint area. Sources of optical radiation in the
welding arc are: the arc column, the regions close to electrode, the liquid metal transported across the
welding arc, the molten pool, the heated region of the base material around the molten pool and the
heated end of the electrode wire [1] . This way the optical radiation from the whole range of ultraviolet
(UV), visible (VIS) and infrared (IR) radiation is a byproduct of the welding process. The 2006/25/EC
Directive [2] is an obligatory document for all European Community countries which specifies minimal
requirements related to the health and safety of workers exposed to artificial optical radiation. It lays
Submitted to Energies, pages 1 – 18
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down both the criteria and scope of risk assessment and exposure limit values (ELVs) to eyes and skin
to avoid adverse effects due to exposition to artificial optical radiation. The Directive has its scientific
basis on the ICNIRP’s (International Commission of Non-Ionizing Radiation Protection) guidelines
from 2004 [3] and the ELVs for UV radiation haven’t been changed in the newest ICNIRP statement
for UV protection of workers published in 2010 [4]. Directive statements had to be implemented
into the law in each EC countries until 2011. Risk assessment is the scientific approach to identify
and quantify health hazards due to optical radiation [5] and obligatory to preform by employers. It
means that each source of optical radiation in working environment should be identify and then risk
assessment performed. But the determination of exposure level is often not a trivial task, especially for
technological, not stable in time sources, like welding arcs.
Welding arcs belong to the strongest technological sources of artificial optical radiation, especially
in ultraviolet and visible range [5–15]. It creates a wide range of risks for skin and eyes both for welders
and workers / people surrounding welding workstation [13,14,16–21]. Strong UV radiation is emitted
by welding arc into surrounding environment and large numbers of workers at workplaces, where
welding is performed, are exposed to UVR. Among those workers are not only professional welders
but also not professional welders, who perform welding occasionally or are engaged in non-welding
tasks [14]. The measurements in the surroundings of welding arc showed that actinic radiant exposure
(i.e. 8-hour dose) for non-welding workers could reach about 360 J/m2 (it corresponds to 12xELV,
where ELV = 30 J/m2 ), and even about 164 J/m2 (5.5xELV) in the non-welding areas what substantially
pose health risk to all nearby workers [15,20]. The exposure to optical radiation when striking the arc
for nearby workers could also rise hazard for eyes [7,9,14,22,23].
The worldwide population of professional welders is estimated as more than 3 million [21,24] but
it is estimated that more than 110 million workers across the world are exposed to welding related
radiation [25]. It constitutes a significant number of workers who works in hazardous environment
related to welding. UV radiation emitted by welding arc is one of the most important physical agent to
consider during risk assessment. Exposure to UVR is a risk factor of the development of: erythema
[17,26], sunburn /burn [24,25], actinic keratosis [24,26], skin cancer: basal cell carcinoma – BCC and
squamous cell carcinoma – SCC [18,24,25], cutaneous malignant melanoma – CMM [24,26], cataract
[21], photokeratoconjunctivitis often known as "welders flash" [26,27] and ocular malignancy [18].
The International Agency for Research on Cancer (IARC) has identified ocular melanoma in welders
as the main health adverse effect due to UV radiation emitted by welding arc (IARC). In everyday
practice acute health effects of UV radiation, especially "welders flash", occur frequently at workplaces
where welding has being performed. It concerns both welders and workers in the vicinity of welding
workstation [14].
As it was mentioned before, Directive [2] refers to the risks to the health and safety of workers
due to adverse effects caused by exposure to artificial optical radiation to the eyes and skin. The
requirements included in this Directive apply workers exposed to optical radiation emitted by welding
arc, both welders and workers who perform theirs tasks nearby the welding station. The employer
is obligated to perform the risk assessment arising from optical radiation for all employees who
are exposed to this radiation. It means not only welders. To do this, the appropriate exposure
level assessment should be designated. In the case of welding, it is usually determined based on
measurements results at workstations. The exposure level has to be evaluated in relation with Exposure
Limit Values (ELVs) [2].
The measurement of optical radiation emitted by welding arc is not a trivial task. Mainly
because of unstable in time arc emission, especially on the beginning – during arc ignition. The arc
ignition process affects the subsequent arc welding process [28] and then stable welding process
which is essential for good joint quality [1]. For this reason there are several methods of arc stability
determination based on measurements and analysis of welding current intensity and voltage [29],
noise emitted, arc light emission [1] or acoustic emission from material. According to Suban and
Tusek, an ideal welding arc could be characterized by at least following properties: a uniform material
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transfer, constant arc length and no spatters. It was proved that some welding parameters could
influence the arc stability. For example analysis of MIG/MAG (Metal Inert Gas / Metal Active Gas)
welding process stability showed that type of shielding gas influences the stability and should be
selected according the material transfer mode [29] measurements of optical radiation from welding
arc for hazard evaluation were the subject of different studies. The strong influence of welding
parameters on UV radiation emission was proved [8,10,14,30]. The relative spectrum of arc emission
depends mainly on welded material chemical composition, but the absolute intensity of the radiation
depends on the wire/electrode diameter, electrode material chemical composition, current intensity
and voltage of arc [5,8,10,13]. For example study of Nakshima et al proved that the UV emission is
more hazardous when the welding materials include magnesium and electrodes contain oxides yield
[14]. The other study of Garcia-Guinea et al put attention on the relationship between ultraviolet
emission and consumable electrodes coatings mineralogy [30]. Strong effective irradiance dependence
on the direction of emission from the arc was also proven [10,14]. The study of Okuno et al for MAG
welding with CO2 shielding gas showed that the maximum emission was at 50◦ -60◦ from the surface
of the base metal. The other study of Nakshima et al carried out for TIG welding showed the highest
effective irradiance at 40◦ from the base metal but at the same time there was found no dependence
of effective irradiance versus angle of inclination with respect to the welding direction [14]. The
differences between angles of maximum emission could be the result of different characteristic of
reflected radiation from the welded materials, because at those angles (40◦ − 60◦ ) both direct and
indirect UV (reflected from welding pool etc) radiation were measured.
The changes of UV emission during arc ignition are mentioned in many articles [7–10,12,14,15].
But the literature review showed that only one publication from 1985 [7] was focused on optical
spectra study for arc ignition. In that time Eriksen used for measurements Diode Array Radpid Scan
Spectrometer (DARSS), which gave him possibility to measure complete spectrum in UV and visible
range in 5 ms [7]. Eriksen’s study was carried out for MIG welding and showed that after only one
arc ignition (lasting less than 50 ms but of emission exceeding more than 10 times the steady state of
arc burning) the ELVs were much exceeded [7]. However in the later article from 1991 he wrote that
ignition phase of MIG/MAG welding arcs lasts approximately 25 ms [6]. It seems strange that for
about 30 years nobody else has not focused on this interesting phenomenon in relation to UV or blue
light hazard evaluation (based on published studies available for authors for the literature review),
except for conference paper in 2018 [23]. However in some studies concerned optical hazard evaluation
from arc welding the high increase of optical radiation emission during arc ignition was mentioned
[8–10,12,14,15], and usually referred to that only one study of Eriksen [7]. The others studies related to
UVR exposure assessment exclude arc ignition emission, usually starting the measurement (or analysis)
after arc ignition [8–10,13,14]. Depending on the study and measuring equipment (polysulfone film,
radiometer, CCD spectroradiometer) the single (or continuous) measurement duration of arc radiation
(after arc ignition) was from the range between 5s and 50s, for example: 6 s [9], 50 s [12], 10 s [5], 5 s
[14] and 15 s [13].
It could be concluded, that previous studies confirmed that:
• UVR emitted by welding arc is highly hazardous not only for welders but also for non-welders
performing the work in the surrounding of welding, which is reflected in skin and eyes diseases
related to UV exposure among that population,
• ELVs to arc ignition could result in exceeding allowable daily exposure.
The development of measurement techniques makes possible to take again the challenge of
determination the actinic radiant exposure from arc ignition to evaluate the actinic UV hazard and
compare results with previous study of Eriksen [7]. Previous studies carried out by authors [23]
indicated that the duration of UV radiation peak of arc ignition could be in range from 20 ms to
220 ms depending on the welding technique and those results were consistent with Eriksen’s [7].
The estimated actinic irradiance during ignition phase was 1.2 to 5 times bigger than average actinic
irradiance after ignition (maximum 26 times bigger for the worst case). It corresponded to actinic
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radiant exposure of 30 J/m2 reached in duration from 0.5 s to 37.5 s in average conditions and 0.1 s for
the worst case [23].
This article presents a new measurement method of UV radiation emitted during the arc ignition
phase based both on CCD spectroradiometric measurements of irradiance spectra and on quick
photometer/flicker meter (based on photodiode) for measurements of photocurrent distribution over
a time. Based on set of measurements carried out for Pulsed Gas Metal Arc Welding (MAG-P) for
different welding currents the hazard evaluation during welding arc ignition phase was performed
using two approaches of actinic radiant exposure determination. The special attention was paid to
actinic hazard to eye over the aversion response time during the unintentional exposure of unprotected
eye could have adverse health effect for workers in the vicinity of welding workstation. The aim of the
article is to present a new proposition of evaluation of UV hazard from welding arc ignition phase
using a CCD spectroradiometer combined with photometer / flicker meter.
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2. Materials and Methods
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Previous studies [23] have concerned the evaluation of UVR hazard during the arc ignition phase
in three welding processes: TIG (Gas Tungsten Arc Welding), MAG and MAG-P. Welding arc ignition
phase was recorded with photometer capable to perform sampling with frequency 50 Hz. However the
analysis of results obtained in that study suggested that improvement of the photocurrent recording
quality during ignition phase is needed, because the shape of peak values of photocurrent was not
precisely mapped. More accurate determination of actinic radiant exposure during the arc ignition has
been needed. Therefore for ignition phase photocurrent recording an improved measuring equipment
has been used in presented research. The range of investigated welding processes has been limited to
one welding process MAG-P.
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2.1. Site
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The studies were conducted in controlled environment of welding laboratory of leading polish
welding research centre – Instytut Spawalnictwa. A laboratory room was a large ventilated room
of dimensions: The walls and ceiling was painted with coating dedicated for welding rooms. The
welding workstation were equipped dedicated local exhaust ventilation system which was removing a
fumes, dust and gases without disturbing the airflow around the arc. The surrounding of welding
workplace was darkened by means of black welding screens, blinds and curtains to reduce influence
of reflected UV radiation on measured data. The illuminance of measurement area was reduced to
around 2.5 lx.
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2.2. Welding process characteristic
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MAG-P process is commonly used in the Polish industry. It can be characterized by presence
of noticeable period of increased optical radiation at the beginning of welding which is the subject
of this research. Welding arc parameters for the process such as current, voltage, gas flow and wire
speed were controlled by automated welding workstation KEMPPI PRO5200. This choice allowed
to reduce arc instability resulting from the limited precision of electrode guidance during manual
welding. Measurements were performed for five settings of welding current: 70 A, 100 A, 120 A, 180
A and 240 A. The welding electrode was mounted in constant position while welded material was
mounted on motor-driven rotating stage (Figure 3). Welding parameters are presented in Table 1.
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Table 1. MAG-P welding parameters.
Parameter
Shielding gas
Ar+18%CO2 +
+2%O2
Gas flow
12 l/min
Welding current
70–240 A
Length of arc
12 ± 1 mm
Welding wire
G3Si1 1.0 mm
Welded material
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Welding process
MAG–P
Construction steel
2.3. Measuring equipment
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Distinguishing feature of the new method of the UV hazard evaluation is simultaneous use of two
measuring devices: spectroradiometer based on CCD array detector and photometer/flicker meter
using silicon photodiode. The recording with photometer/flicker meter was registering about 5.5 s.
It started 1–2 s before arc ignition and lasted during arc ignition phase and about 3–4.5 s after arc
ignition. The spectroradiometer recording lasted from 10 s (10 repeated registrations). It was started
1–2 s after arc ignition phase what was adjusted to observation of welding arc when the arc seemed to
burn "smoothly". The approximate duration of arc ignition was less than 50 ms what corresponds with
Eriksen studies [7].
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2.3.1. Spectroradiometer system for spectral irradiance recording
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Measurements of average spectral irradiance during arc operation were performed with
spectroradiometer system GL Spectis 5.0 Touch manufactured by GL Optic. The spectroradiometer
communicates with a PC via USB connection with spectral analysis software (GL SpectroSoft) for data
analysis. This software is used to perform spectroradiometric measurement and read these values
in realtime interface. The true irradiances of a spectrum are displayed in table and on the graph in
actual mW/(m2 nm). Additionally GL SpectroSoft provides automatic calculation of whole range of
UV parameters needed for photobiological hazard evaluation (Figure 1).
The CCD spectroradiometer is based on back-thinned type CCD detector combined with reflective
diffraction grating and allows to perform measurements in wide spectral range 200 nm -– 1050 nm.
The device is characterized by low level of stray light which is 2*10e−4 according to manufacturer
specification presented in Table 2. Considering stray light level declared by manufacturer, possible
influence of daylight on measured irradiance in the UV range caused by stray light can be neglected.
Table 2. Specification of GL Spectis5.0 Touch spectroradiometer.
Parameter
Specification
Spectral range
200 nm – 1050 nm
Optical FWMH
2.5 nm – 3.5 nm
Wavelength reproducibility
0.5 nm
Stray light
2*10E-4
Signal to noise ratio
1000:1
Integration time
10 ms – 60 s
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Figure 1. The view of window of GL SpectroSoft software presenting measured spectrum, table
with measurement results for particular weavelengths and selected results of calculations like: total
UV irradiance, actinic irradiance, UVA irradiance and blue light hazard irradiance (example for
current 120 A)
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The irradiance probe of this instrument allows for extended spectral range measurements
and can be used for the assessment of photobiological safety in conformity with EN 14255-1 [31].
Spectroradiometer probe had 10 mm diffuser made from quartz glass which guaranteed the correct
transmittance in the UV range and provided cosine corrected response in class A (f2 <1.5%) The probe
was connected to the device by means of 1.5 m quartz fiber glass. Calibration of probe was confirmed
with factory certificate of absolute spectral calibration dated on three months before the measurements
day. Angle of probe observation was limited to 30◦ by means of additional diaphragm.
Factory calibration in UV and blue light range was carried out with deuterium lamp what
ensures higher accuracy in this range with respect to the halogen reference light source. Calibration
was performed by direct comparison with the use of standards of spectral irradiance: VNIIOFI
KGM24-275 No. 0906 tungsten-halogen lamp standard and VNIIOFI DL4 deuterium lamp standard.
Both deuterium lamp and halogen lamp used for calibration of spectroradiometer are The All-Russian
Research Institute for Optical and Physical Measurements Federal State Unitary Enterprise (VNIIOFI)
traceable standards. Expanded uncertainty of spectral irradiance measurement with GLSpectis 5.0
(expanded uncertainty of instrument calibration with coverage probability 95% and k=2) has been
determined according to material available from manufacturer [32] and equals 6% for range 200 nm -–
220 nm, 5% for range 220 nm – 400 nm and 4% for range 400 nm — 1050 nm. In case of welding arc
radiation the main source of random uncertainty is instability of arc radiation which is much higher
that uncertainty of spectroradiometers.
Due to the rapid changes of instantaneous irradiance, automatic adjustment of spectroradiometer
integration time could not be used. The integration time of spectroradiometer had to be manually
adjusted for each measurement according to the maximum level of arc radiation. Adopted welding
currents range (arc radiation) and distance to the MAG-P process welding arc required integration
time of 1 s.
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Changes of dark current of CCD detector were compensated by regular performing of a dark
current compensation procedure available in spectroradiometer software where detector was covered
with opaque material showing non-response of any spectral radiance. Furthermore the test of influence
of electromagnetic emissions was performed to ensure non-response of spectroradiometer system from
electromagnetic frequencies. Welding sessions were preceded with measurement of ambient light. The
results of ambient light measurements were then subtracted from actual welding arc measurements
during the results processing stage.
The average irradiance for each measurement session was calculated as the arithmetic average of
10 recordings, based on the recommendation for good practice in measurements using diode-array
detectors [6].
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2.3.2. Photometer / flicker meter for photocurrent recording
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Due to the constrains of minimum integration time required by the spectroradiometer, variability
of the arc irradiance in the phase of ignition of the welding arc was recorded using photometer / flicker
meter ( GL Photometer03 manufactured by GL Optic).
The selected photometer measures light with silicon diode (manufactured by Hamamatsu).
The device used for experiment was additionally equipped with UV transmitting filter UG-11
(manufactured by Schott). The purpose of this filter was to limit the impact of visible and infrared
radiation on the measurement result, especially radiation from light sources and daylight. Considering
this fact and also low level of illuminance from visible light sources observed at the experiment
workplace, the assumption was made that a change of a recorded detector photocurrent is proportional
to the change of actinic irradiance in UV.
The selected photometer can perform series of measurements with adjustable frequency in the
range from 31.25 kHz to 200 kHz what corresponds to sampling time between 32 µs and 5 µs For
the purposes of the experiment the frequency 31.25 kHz has been selected, since the use of a higher
sampling rate (ie. about 0.03 ms) leads to significant increase of accuracy of recorded distribution
of photocurrent over the time or arc ignition. It’s worth to emphasizing that this is over 6,000 times
higher sampling frequency than used in previous experiments performed by Eriksen [7]. Linearity of
photometer declared by manufacturer is ± 2%.
Figure 2. Example of recorded photocurrent samples for welding current 120 A.
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For investigated welding process a recording of arc ignition phase were performed. First 5.5 s of
welding arc emission was recorded. Selected sampling frequency 31.25 kHz for this duration resulted
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in series of 163,840 samples of a detector photocurrent. Then the actual ignition peak at the very
beginning of welding action was identified and the data before this point were rejected from further
analysis (Figure 2). The average photocurrent of samples series Iavg (in mA) was calculated and the
photocurrent Is of each sample in series was represented as ratio of Is /Iavg .
2.4. Measurement geometry
Measuring head of spectroradiometer and detector of photometer / flicker meter were installed on
tripod in front of rotating welding stage. The position of welding torch was adjusted during welding
to a small extent. Torch position changes were perpendicular to the line of observation determined by
the detectors.
Figure 3. Measurement geometry.
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The distance L between measuring head and welding arc was 1.0 m. The measuring probe was
mounted at the height D = 0.86 m while height d of rotating stage was at 0.76 m (Figure 3). Applied
geometry of measurement resulted in observation angle α between measuring axis and rotating stage
plane equal 6◦ . Although highest actinic irradiance can be expected for observation angle around 40◦
[14] or 50◦ [10], the angle α was selected to capture mostly direct radiation emitted by arc and limit
reflected radiation from welded material.
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2.5. Actinic irradiance
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The analysis of photobiological hazard presented in this paper was based on actinic irradiance
Es understand as irradiance within the UV wavelength range 180 nm to 400 nm effective for adverse
effects on human eyes and skin. The actinic irradiance Es is defined as spectral power distribution
spectrally weighted by action spectrum S(λ) defined in Directive 2006/25/EC [2] or ICNIRP [4] and
integrated with Equation 1.
Es = ∑ E(λ) · S(λ) · ∆λ
(1)
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where:
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Es
E(λ)
S(λ)
∆λ
= actinic irradiance (W/m2 )
= spectral irradiance from measurement (W/(m2 nm) )
= relative spectral effectiveness factor
= bandwidth of the measurement.
Tmpe =
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Es
(2)
The Equation 2 express maximum permissible exposure time based on actinic ELV. In case of GL
Spectis 5.0 Touch used for spectral measurement, effective irradiance Es as well as other parameters
related to photobiological hazard evaluation are automatically calculated by analytic software GL
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SpectroSoft provided together with spectroradiometer (Figure 1). The actinic irradiance is expressed in
Watts per square meter (W/m2 ). Actinic irradiance accumulated in selected time interval is defined as
actinic radiant exposure.
The base for evaluation of actinic irradiance of ignition peak was the arithmetic average of actinic
irradiance Esavg of 10 spectroradiometric measurements (performed after ignition phase). For each
series of 10 measurements the maximum Esmax , the mimimum Esmin and the arithmetic mean Esavg
were calculated. Then the standard deviation of mean σ ( Esavg ) were determined. Based on it the
expanded uncertainty U ( Esavg ) estimated for coverage factor k = 2.
The actinic irradiance of each sample Esample was referred to average actinic irradiance Esavg ,
average photocurrent Iavg and photocurrent Is of each sample in series, and was calculated according
to equation 3.
Table 3. Statistical measures of actinic irradiances .
Welding
Average
Minimum
Maximum
Standard
Expanded
current
actinic irradiance
actinic irradiance
actinic irradiance
deviation
uncertainty
k=2
Esavg
Esmin
Esmax
σ ( Esavg )
U ( Esavg )
A
W /m2
W /m2
W /m2
W /m2
W /m2
70
0.88
0.82
0.97
0.01
0.03
100
1.51
1.07
1.82
0.07
0.14
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2.28
1.86
2.75
0.08
0.16
180
1.94
1.43
2.48
0.11
0.22
240
2.12
1.36
2.82
0.14
0.27
Esample = Esavg · Is /Iavg
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(3)
2.6. Actinic radiant exposure determination
Two approaches have been used in current study to determine actinic radiant exposure during
the arc ignition phase and then to be applied for actinic hazard evaluation of eyes during aversion
response time. The first approach, used also in previous research [23] is based on calculation as a
product of maximum registered actinic irradiance of arc ignition (maximum peak actinic irradiance)
E peak1 and duration of arc ignition Tpeak (without consideration of the shape of that peak output) (see
Figure 4). The duration of ignition was defined for purpose of these calculations as a period during
first 50 ms of welding action (according to [7]) when the recorded actinic irradiance Esample was higher
than average actinic irradiance Esavg (Figure 4).
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Figure 4. Distribution of actinic irradiance Esample (t) over eye aversion response time (example for
current 120 A).
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The weighted average (Equation 4) was used to calculate total actinic irradiance Et1 (index 1
means first approach) corresponding to eye aversion time Tavr and in the next step total actinic radiant
exposure Ht1 during this period (Equation 5). The assumption was that Tpeak duration will not exceed
eye aversion time Tavr equal 0.25 s. A maximum permissible time of exposure Tmpe1 were calculated
for each welding current with Equation 7 based on ELV = 30J/m2 [2].
Et1 =
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E peak · Tpeak + Esavg · ( Tavr − Tpeak )
Tavr
(4)
Ht1 = Et1 · Tavr
(5)
Et1 = Ht1 /Tavr
(6)
Tmpe1 = 30/Et1 = 30 · Tavr /Ht1
(7)
The results of previous studies based on this method [23] indicated the possibility of exceeding of
Exposure Value Limit (ELV) for MAG-P process with just one glance from distance of 1.4 m. However,
further analysis of arc radiation runs obtained in that studies suggested that improving the quality
of recording of ignition phase may lead to more accurate determination of actinic radiant exposure
taking into account not only its maximum value but the real shape of the peak output.
Therefore the second approach used in current studies is based on an integration of recorded
irradiances during the ignition phase taking into account the real shape of the peak output (Figure 4).
This new approach was possible due to use more adequate device for recording of photocurrent to
determine the shape of the peak and then calculation of actinic irradiance.
Actinic radiant exposures in this approach were calculated by summation of individual actinic
irradiances Esample obtained from Equation 3 (Figure 5). Actinic radiant exposure of peak H peak2 (index
2 was used for second approach) was calculated using Equation 8 while total actinic radiant exposure
Ht2 with Equation 9. Adequately to first approach, the maximum permissible time of exposure Tmpe2
was determined with Equation 11.
Tpeak
H peak2 =
∑
t =0
Esample (t) · ∆t
(8)
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Figure 5. Distribution of actinic radiant exposure integrated over eye aversion response time (current
120 A)
Tavr
Ht2 =
∑ Esample (t) · ∆t
(9)
t =0
Et2 = Ht2 /Tavr
(10)
Tmpe2 = 30/Et2 = 30 · Tavr /Ht2
(11)
305
The results obtained from both approaches were compared to determine the differences in
evaluation of UV radiation actinic hazard during the welding arc ignition and the potential impact of
applied approach on risk assessment.
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3. Results
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304
307
308
309
310
311
312
313
314
315
316
317
318
For each of registered distribution of photocurrent over the time the ignition peak can be identified
although higher actinic irradiances were observed for lower welding currents. Duration of ignition
peak Tpeak was varying in range 0.009 s – 0.015 s. Total actinic radiant exposure during adopted 0.25 s
(equal to eye aversion response time) after start of ignition of welding arc were calculated according to
both mentioned before approaches. Total actinic radiant exposures calculated for duration longer than
adopted eye aversion time are presented in Appendix A.1.
The results of first approach of UV evaluation are presented in Table 4. Data obtained with the
first approach can be characterized by large data scatter. It is shown that maximum peak actinic
irradiance tends to be the biggest for the smallest welding arc current 70 A, then decreases at 100 A,
and increases at 120 A, and finally again decreases at 180 A where is its minimum. At the first glance
it was surprising for us, so we repeated few times measurement series for that currents. The results
presented the same tendency.
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Table 4. Actinic irradiance and actinic radiant exposure corresponding to eye aversion response time
Tavr = 0.25 s based on first approach of UV actinic hazard evaluation.
Welding
Maximum peak
Peak
Peak actinic
Average
Total actinic
current
actinic irradiance
duration
radiant exposure
irradiance
radiant exposure
E peak1
Tpeak
H peak1
Esavg
Ht1
A
W /m2
s
J/m2
W /m2
J/m2
70
41.60
0.014
0.58
0.88
0.79
100
21.51
0.012
0.26
1.51
0.62
120
38.72
0.015
0.58
2.28
1.12
180
11.94
0.009
0.11
1.94
0.58
240
12.42
0.015
0.19
2.12
0.68
Table 5. Actinic radiant exposure corresponding to eye aversion response time Tavr = 0.25 s based on
second approach of UV actinic hazard evaluation.
Welding current
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
Peak actinic
Total actinic
Ratio
radiant exposure
time
radiant exposure
H peak2
Ht2
Ht1 /Ht2
A
J/m2
J/m2
70
0.15
0.27
2.93
100
0.09
0.26
2.38
120
0.17
0.53
2.11
180
0.06
0.42
1.37
240
0.08
0.73
0.94
When we consider average actinic irradiance after ignition phase, the increase with the welding
current is observed, however not simply proportional to welding current, and in the range between
120 A and 240 A seems to be approximately constant. So it could mean that it was probably related to
the change in the mode of metal transfer in the arc during ignition and increasing amount of welding
fumes close to the arc. The decrease of irradiance in the range of welding arc currents between 240 A
and 400 A was also observed by Okuno et al [10] during measurement of effective irradiance during
MAG welding with solid wire. The authors [10] suggested that the change in the mode of metal
transfer in the arc from dip mode through globular mode to spray mode could be potential reason of
that.
As the product of maximum peak actinic irradiance and peak duration, the maximum peak
actinic radiant exposure for 70 A was about 5.3 times bigger that for 180 A. But when we compare
the total actinic radiant exposure for different welding currents the biggest one is for 120 A, and it is
1.9 times bigger than for 180 A (the smallest one). However the big difference in peak actinic radiant
exposure between 70 A and 180 A has been "compensated" during the arc emission after ignition (over
0.25 s), so the ratio of total actinic radiant exposures decreased to about 1.4. The calculated peak actinic
radiant exposure and total actinic radiant exposure Ht2 of welding arc determined with the second
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337
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341
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approach are presented in Table 5. Additionally, the last column presents the ratio between total
radiant exposures determined using both approaches. Calculations of radiant exposure were based on
the same average actinic irradiances Esavg and recorded data as in the first approach. The peak actinic
radiant exposure was the biggest for 120 A and approximately the same for 70 A welding current. The
smallest one was for 180 A. The ratio between maximum and minimum of above mentioned values
was 2.83. Still when we look at total actinic radiant exposure we can observe its increase with welding
current increasing, with one exception for 180 A. The biggest one is for 240 A, and the smallest for
100 A giving the ratio biggest/smallest of 2.81.
The last column in Table 5 presents ratio of total actinic radiant exposures obtained using both
approaches. This way we could see the differences of determined radiant exposures for actinic hazard
evaluation. It could be noticed that with increase of the welding current the ratio decrease from about
3 (at 70 A) to about 1 (at 240 A). It proves overestimation of radiant exposure using first approach
especially for smaller welding currents. But for the longer time of exposure like 3 s, the ratio of actinic
radiant exposures is approximately about 1.0 what suggests that the approach used for calculation is
less significant and the contribution of peak radiant exposure decreases (see Appendix A.1).
Figure 6. Distribution over the time of actinic radiant exposure for different welding currents.
350
351
352
353
354
355
356
357
358
359
360
361
362
363
The Figure 6 shows the distribution of actinic radiant exposure over the time for different welding
currents. The slopes of plots present the radiant exposure grow rate for particular welding currents. It
could be concluded that for smaller welding arcs the radiant exposure grows rapidly to higher values
during ignition and then slowly increases in the rest of time . In contrary for bigger welding arcs
radiant exposure grows less rapidly and to a smaller values during ignition time and then evenly
and almost linearly increases in the rest of the time. The higher current the bigger grow rate. It also
indicates the contribution of peak radiant exposure in total radiant exposure, is bigger for smaller
currents than for higher currents.
The contribution of peak radiant exposure in total radiant exposure obtained using both
approaches are presented in Figure 7. The first approach of actinic radiant exposure determination for
hazard evaluation results in much bigger contribution of peak actinic radiant exposure in total radiant
exposure than in the second approach. The maximum difference is about 20 % (for 70 A and 120 A)
and the smaller about 4 % (for 180 A). The decrease of that contribution with the increasing of welding
current is also visible on this figure.
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Figure 7. Contribution of peak actinic radiant exposure in total actinic radiant exposure for different
welding currents.
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365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
4. Discussion
Due to the adopted measurement geometry, the obtained results of actinic irradiance and total
actinic radiant exposure are lower than the maximum results recorded for the MAG-P or MAG
processes in similar conditions reported in other papers [6,10,23]. Determination of maximum possible
actinic irradiances at the accepted distance from welding and height of probe above the floor arc was
not a goal of this study. However relation between increase of actinic irradiance of ignition phase and
average actinic irradiance of welding action should be approximately the same in all directions of arc
emission, what we assumed in our analysis.
Improved method of recording variability of welding arc ignition allowed for a more accurate
mapping of the peak output shape of arc ignition and thus a more precise determination of its duration
and the maximum value. The ratio of maximum peak irradiance and average irradiance (during
the "stable" phase of arc emission) was in the range between about 6 and 47, what showed that the
irradiance peak during ignition phase could be much bigger than 10, as it had been stated by Eriksen
[6]. The new method of registration allowed to discover this. The range of duration of ignition peak
identified using new photometer / flicker meter showed that the peak duration was narrower than
ranges determined in previous studies i.e. 25 ms and 50 ms. [6,7,23]. It suggests that actinic radiant
exposure of UV during arc ignition evaluated on base of previous results can be overestimated and then
the hazard evaluation. The higher accuracy of measurement obtained thanks to proposed new method
of measurement can be expected to provide lower measurement error what is crucial for determination
of expanded uncertainty which should be not bigger than 30% according to EN 14255-1 [31]. Taking
into account wide range of uncertainty components related to arc welding (fumes, instability of arc
emission during the time, arc movement, reflections from welding area and surrounding etc.), the
efforts should be focused on reducing any measurement errors both related to measurement geometry,
measurement processing procedure and measurement equipment quality.
Another important aspect which strongly influences the determined parameters for UV hazard
evaluation is the way of calculation of parameters based on obtained measurement results. As it was
presented in the article consideration or not he phase of arc ignition for short duration exposures
(like eye aversion response) in actinic hazard evaluation of eye could have critical consequences. For
investigated MAG-P welding process, omission of peak radiant exposure especially for low welding
currents (between 70 A – 120 A) could result in 44% – 66% decrease of calculated radiant exposure.
Version January 9, 2019 submitted to Energies
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417
Going forward, the determined maximum allowed time of exposure will be longer than it should be
and as a consequence will lead to increased hazard for worker related to overexposure to UV radiation.
The next important aspect is the determination of actinic radiant exposure used for photobiological
hazard evaluation. Integration of actinic irradiances applied for determination of total actinic radiant
exposure in second approach leads to the more precise determination of the actinic hazard, especially
for short exposure time including ignition of arc (with special attention to aversion response time). For
MAG-P welding it is significant especially for smaller welding currents (70 A - 120 A) and for currents
above 200 A it seems to be not so important (see Table A3) .
For both approaches the same tendency may be observed. As the welding current increases,
the significance of ignition peak actinic radiant exposure for total actinic radiant exposure decreases
(Figure 7). The ratio Ht1 /Ht2 decreases with increasing welding current what corresponds with lower
contributions of peak actinic radiant exposure in total radiant exposure presented on Figure 6 and
Figure 7.
However the results of total actinic radiant exposure during eye aversion time were much lower
than exposure limit values 30 J/m2 what means that single glance of unprotected eye at arc ignition
does not pose the high risk of adverse effect. But multiple glances could lead to high risk of acute
effect like photoceratoconjunctivity "welding flash" what was stated in other publications [7,10,14].
Unprotected skin especially of head or neck, can be exposed to welding arc radiation for longer time
because of lack of aversion response time. Importance of this fact both for welders and non-welders
were underlined by Tenkate [15,20]. So for this reason the maximum permissible exposure time was
determined in our study (Appendix A1). It was in the range of from 7 s to 13 s (first approach) and 10 s
to 29 s (second approach). But both in our study and other published studies [10,11,14,20] the total
daily exposure time of unprotected parts of skin to UV arc radiation could be easily much longer than
permissible exposure times.
418
5. Conclusions
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
While the exposure is brief for each arc ignition, if this occurs many times in a workday,
the total actinic radiant exposure may become sufficient to cause acute adverse effects like
photoceratoconjunctivitis, erythema and burn. If it will be repeated for a many days the chronic
adverse effects of prolonged exposure to UV like ocular malignancy, actinic keratosis or different kind
of skin cancer could appear. In fact the total exposure time can easily exceed the permissible exposure
time obtained in our study, i.e 7 s - 29 s at the distance of 1 m from the arc. It means that UV radiation
form MAG-P arc welding is actually hazardous for the eyes and skin not only for welders but also for
workers in the vicinity of welding arc.
The presented measurement method using CCD spectroradiometer and photometer /flicker
meter enables determination of radiant exposure of arc ignition radiation. This method is especially
recommended for UV hazard evaluation of eyes during the aversion response time exposure.
Additionally it provides reduce of the uncertainty of welding arc emission measurements for the
needs of determination parameters for photobiological hazard evaluation through the limiting the
errors related to measurement method. Proposed method could be easily expanded to other hazards
related to optical radiation emitted by welding arc, especially for blue light hazard evaluation.
The way of determination UV radiant exposure during the arc ignition time, based on obtained
measurements results, has the significant influence on hazard evaluation. For MAG-P welding process
and considered welding currents it was especially significant for exposure duration below 3 s. The
measurements using the same method should be continued for the other welding techniques and
welding parameters to determine characteristic dependencies occurring during arc ignition.
It is important to promote knowledge about the new methods of photobiological hazard
evaluation among possibly wide range of health safety officers, employees and other experts who
perform risk assessment which will contribute to the quality of hazard evaluation and will help to
improve occupational safety.
Version January 9, 2019 submitted to Energies
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Author Contributions: conceptualization, Andrzej Rybczyński and Agnieszka Wolska; methodology, Andrzej
Rybczyński, Tomasz Pfeifer and Jolanta Matusiak; validation, Andrzej Rybczyński and Agnieszka Wolska; formal
analysis, Andrzej Rybczyński and Agnieszka Wolska; investigation, Andrzej Rybczyński, Agnieszka Wolska,
Mariusz Wisełka and Jolanta Matusiak; resources, Agnieszka Wolska ; data curation, Andrzej Rybczyński;
writing—original draft preparation, Andrzej Rybczyński; writing—review and editing, Agnieszka Wolska.;
visualization, Andrzej Rybczyński.; supervision, Agnieszka Wolska; project administration, Agnieszka Wolska.;
funding acquisition, Agnieszka Wolska”.
Funding: This paper has been based on the results of a research task carried out within the scope of the fourth
stage of the National Programme "Improvement of safety and working conditions" partly supported in 2017–2019
— within the scope of research and development — by the Ministry of Family, Labour and Social Policy. The
Central Institute for Labour Protection – National Research Institute is the Programme’s main co-ordinator.
Acknowledgments: We would like to thank to Instytut Spawalnictwa (Welding Institute) for providing access to
the MAG-P welding workstation, provided welding materials and technical support during measurements.
458
Conflicts of Interest: The authors declare no conflict of interest.The funders had no role in the design of the study;
in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish
the results.
459
Abbreviations
460
The following abbreviations are used in this manuscript:
456
457
461
462
CCD
ELV
FWMH
MAG
MAG-P
MIG
TIG
UV
UVR
463
Appendix A
464
Appendix A.1
465
466
467
468
Charge-coupled device
Exposure limit value
Full width at half maximum
Metal Active Gas
Metal Active Gas – Pulse
Metal Inert Gas
Tungsten Inert Gas
Ultraviolet
Ultraviolet radiation
Calculation of total actinic radiant exposure estimated for eye or skin actinic hazards (for time
duration longer than eye aversion time i.e.: 0.05 s (arc ignition duration according to Eriksen [7] , 1 s, 2
s and 3 s) are presented in Table A1 and Table A2. Table A3 presents ratio between total actinic radiant
exposures obtained with both approaches.
Table A1. Actinic radiant exposure Ht1 corresponding to different time duration, based on first
approach of UV hazard evaluation.
Welding current
Total actinic radiant exposure over a time
0.05s
1s
2s
3s
A
J/m2
J/m2
J/m2
J/m2
70
0.61
1.45
2.33
3.21
100
0.32
1.75
3.26
4.77
120
0.66
2.83
5.11
7.40
180
0.19
2.03
3.97
5.91
240
0.26
2.27
4.39
6.51
Version January 9, 2019 submitted to Energies
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Table A2. Total actinic radiant exposure Ht 2 corresponding to different time duration based on second
approach of UV hazard evaluation.
Welding current
Total actinic radiant exposure over a time
0.05s
1s
2s
3s
A
J/m2
J/m2
J/m2
J/m2
70
0.17
0.76
1.76
2.68
100
0.12
1.16
2.73
4.37
120
0.21
1.98
4.25
6.84
180
0.12
1.95
3.93
5.82
240
0.26
2.50
4.61
6.46
Table A3. Ratio of actinic radiant exposures Ht1 /Ht2 .
Ratio Ht1 /Ht2
Welding current
469
References
470
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471
472
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473
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7.
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8.
9.
10.
0.05s
1s
2s
3s
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3.61
1.91
1.32
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2.63
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1.09
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3.15
1.43
1.20
1.08
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1.56
1.04
1.01
1.02
240
1.63
0.91
0.95
1.01
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