ESAB m3 G2 System Manual page 61

section 6
Danger
A hazard exists whenever a water table is used with plasma arc cutting. Severe explosions have resulted from the ac-
cumulation of hydrogen beneath the plate being cut. Thousands of dollars in property damage have been caused by
these explosions. Personal injury or death could result from such an explosion.
The best available information indicates that three possible sources of hydrogen exists in water tables:
1. molten metal reaction
Most of the hydrogen is liberated by a fast reaction of molten metal from the kerf in the water to form metallic ox-
ides. This reaction explains why reactive metals with greater affinity for oxygen, such as aluminum and magnesium,
release greater volumes of hydrogen during the cut than does iron or steel. Most of this hydrogen will come to the
surface immediately, but some will cling to small metallic particles. These particles will settle to the bottom of the
water table and the hydrogen will gradually bubble to the surface.
2. slow chemical reaction
Hydrogen may also result from the slower chemical reactions of cold metal particles with the water, dissimilar metals,
or chemicals in the water. The hydrogen gradually bubbles to the surface.
3. plasma & shield gas
Hydrogen or other fuel gases, such as Methane (CH
used plasma gas. This gas is 35% hydrogen by volume. When using H-35 at high currents, as much as 125 cfh of
hydrogen will be released.
Regardless of the source, the hydrogen gas can collect in pockets formed by the plate being cut and slats on the
table, or pockets from warped plate. There can also be accumulation of hydrogen under the slag tray or even in the
air reservoir, if these are part of the table design. The hydrogen, in the presence of oxygen or air, can then be ignited
by the plasma arc or a spark from any source.
4. follow these practices to reduce hydrogen generation and accumulation:
A. Clean the slag (especially fine particles) from the bottom of the table frequently. Refill the table with clean water.
B. Do not leave plates on the table overnight or a weekend.
C. If a water table has been unused for several hours, vibrate it in some way before the first plate is laid in position.
This will allow accumulated hydrogen in the refuse to break loose and dissipate before it is confined by a plate
on the table. This might be accomplished by laying the first plate onto the table with a slight jolt, then raising
the plate to permit hydrogen to escape before it is finally set down for cutting.
D. If cutting above water, install fans to circulate air between the plate and the water surface.
E. If cutting underwater, agitate the water under the plate to prevent accumulation of hydrogen. This can be done
by aerating the water using compressed air.
F. If possible, change the level of the water between cuts to dissipate accumulated hydrogen.
G. Maintain pH level of the water near 7 (neutral). This reduces the rate of chemical reaction between water and
metals.
hydrogen explosion hazard! read the following before attempting
to cut when using a water table.
), may come from the plasma or shield gas. H-35 is a commonly
4
pt-36 plasma torch
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