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Contents
The welders working environment
4
Electricity
4
Electromagnetic fields
7
UV, IR and visible light radiation
9
Air pollution in connection with welding
11
Fire and spatter
15
Noise risks
17
Ergonomics
18
Machine safety and mechanical protection
20
The cutting operators environment
22
Risks and measures with gas cutting
22
Risks and measures with plasma cutting
23
Under water plasma cutting
24
Risks and measures with laser cutting
24
Laser protection class 4
24
Laser protection class 1
25
Risks and measures with waterjet cutting
26
Reference literature
27 4
The welders working environment
Welders are members of an occupational group which is exposed to a
number of different environmental problems. This booklet deals with the
different factors in the welders working environment, as well as suitable
measures that can be implemented to improve this environment and
reduce the health risks. Effective protection can reduce the health risks.
A good welding environment is far more important, however. Access to
qualified welders is essential to obtain good quality and productivity.
The working environment is one of the factors that have an effect on the
choice of occupation.
Electricity
Human beings are extremely sensitive to current that passes through
their bodies. Serious physical injury can be caused by currents of just
20 or 30 mA.
Physical injuries, such as falling from scaffolding or a ladder, can result
indirectly from very low currents as a result of a sudden and
uncontrollable reaction to an electric shock.
Figure 1. Time and current dependence of alternating current in the frequency
range of 15-100 Hz.
Perceptible current (Zone 1). Alternating
current is perceptible at just 0.5 mA, while the
limit for direct current is around 2 mA. If the
current increases, pain and physical discomfort
are generated, but this normally produces no
harmful physiological effects.
Release limit (Zone 2). Currents above the
release limit produce muscular spasm and the
inability to release the live component of ones
own free will. It is also difficult to breathe,
especially if the current lasts for longer than
two seconds. Normally, no damage is done to
tissue and internal organs before the next
threshold value is passed.
The next threshold value, auricular fibrillation
(Zone 3), depends very largely on the build of the
victim, but it also depends on how long the
current lasts and the route it takes through the
body, as well as the point in the cardiac cycle at
which the disruption occurs.
Auricular fibrillation means that the ability of the
heart to pump blood ceases. When this threshold
is passed, serious, life-threatening injuries, such
as cardiac arrest, occur, breathing stops and tissue
and internal organs are burned. 5
The choice of the type of current (alternating or direct) during arc
welding is important, as the risks associated with alternating current
(AC) are as much as four times greater than those associated with direct
current (DC).
Risk of electric shocks
The effects that result from current passing through the human body
depend on:
the level and duration of the current
the current path through the body
the frequency of the current
The level and duration of the current
If someone comes in contact with live components, the size of the
current depends on the voltage and the resistance in the current circuit.
The risk of ventricular fibrillation in the heart depends also very largely
on the duration of the current.
The resistance in the current circuit is the sum of the resistance in the
skin, the rest of the body and the protective clothing.
The resistance of the skin depends, among other things, on the
contact area and moisture.
The resistance of a human body, excluding the resistance of the skin,
is comparatively low (can be roughly set at 500 ohm in each arm and
each leg).
Sufficient protective clothing in form of dry leather gloves and shoes
with soles made of rubber.
Figure 2. Statistical values for
total body resistance when
current passes from hand to foot
at 50/60 Hz. For example, the
resistance in 50% of all people is
a maximum of 1,400 ohm when
they are exposed to 230 V (AC).
Figure 2b. Current passing from hand to hand 6
The current path through the body
The danger of ventricular fibrillation in the heart depends on the path of
the current through the body, i.e. the level and time of current passing
through the heart.
The frequency of the current
As mentioned above the risks associated with alternating current are
higher than for direct current. We are most sensitive in the frequency
range of 15-100 Hz.
Welding equipment
Open circuit voltage
The highest permissible open-circuit voltage for a power source
depends on whether it produces direct or alternating current. (Please
note that the EN 60974-1 welding power source standard provides more
detailed information than that which now follows.)
In the case of alternating current (AC), the open-circuit voltage must not
exceed 80 V (rms), but there are some exceptions.
If the equipment is being used in confined space where the risks are
greater (such as moist, hot or confined spaces with conductive parts),
the open-circuit voltage is limited to 48 V (AC). Equipment
suitable for welding with increased hazard of electric shock may
be marked with the S symbol on the rating plate
certain small MMA power sources which often are used at home
can be marked according to the standard EN 50 060 with a limitation
of 55 V (AC).
In the case of mechanised welding in which the welder does not
handle the welding gun manually, 100 V (AC) is permitted.
In the case of direct current (DC), an open-circuit voltage of 113 V
(peak value) is normally permitted, but here, too, there are exceptions
for mechanised welding with a maximum of 141 V and for plasma
cutting, where the live parts are not accessible, with 500 V.
Routine inspection of equipment
If the internal cooling surfaces of a power source are clogged up with
dust and dirt, the temperature increases. It is important from a safety
point of view to avoid overheating. A breakdown of the insulation
between the primary and secondary windings in the transformer may
admit the mains voltage to reach the welding circuit. The insulation
resistance may also deteriorate from conducting dust coming from
grinding.
As the secondary circuit not necessarily is connected to earth, this
would be hazardous to the welder. It is therefore recommended to make 7
routine inspections and cleaning of the internal of the welding power
source.
Protection provided by the enclosure
Power sources should have protection for solid foreign objects and
water penetration provided by the enclosure (IEC 60529). The degree of
protection is indicated by the IP-code (International Protection) on the
rating plate. Power sources for outdoor use shall have a minimum
degree of protection of IP23.
Electromagnetic fields
The question of the health hazards associated with electromagnetic
fields has still not been fully clarified. Even so, straightforward action
may well be justified if it can reduce the level of exposure for people
working in high electromagnetic fields and do so at a reasonable cost.
A low frequency electromagnetic field is a combination of electrical and
magnetic fields but in a given situation, one of them can be dominating.
Electrical fields originate from the voltage. They occur between live
cables or surfaces. Fortunately, it is easy to do something about these
fields using an earthed sheath or screen.
Magnetic fields occur around conductors through which current flows.
The magnetic flux density is measured in tesla (T). In air or other non-
magnetic objects, the flux density is so low that the unit
µ
T is normally
used. A low value for the magnetic flux density for low-frequency fields
is 0.2
µ
T and it is unusual for this value to exceed 1
µ
T in a normal office
environment
Figure 3. A magnetic field quickly decreases as the distance increases. It
decreases most rapidly from a point source, where it declines to one-eighth the
size when the distance doubles. 8
The frequency of the field is important when it comes to its ability to
transfer energy to the surroundings. So, in this way, heat or electric
currents can be generated in surrounding objects.
The welders situation
Welders belong to one of the occupational groups which are exposed to
the highest field strengths. Arc welding requires high welding currents.
The welding equipment may be near the welder and the welding cables
are often in direct contact with the body. In the area close to the welding
cable, the magnetic field exceeds 200
µ
T.
A great deal of welding is performed with direct current. This applies, for
example, to MIG/MAG welding, which is currently the most frequently-
used welding method in industrial applications. Pure direct current
probably has no effect on the health risks but a normal welding current
often have some type of pulsations.
Perhaps the most powerful magnetic fields are found in conjunction with
resistance welding. People with a pacemaker should be especially
careful. It is unsuitable for them to be in the vicinity when resistance
welding is in progress and, in some cases, even when some other type
of welding with high currents is performed. Consult an expert physician.
Measures to improve the welders working situation
A great deal can very definitely be achieved by passing on factual
information about