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Flashbacks
Flashbacks are associated with one or more of the following points. Correct
operating procedures and preventative steps are outlined below:
Agilent 55B AA Spectrometer User's Guide
Keep the burner clean. Cleaning instructions are included in the Burner section
of the Maintenance chapter – Page 91.
Deposits must not be allowed to build up in or on the burner slot because
they can partially block it. Blockages can cause the pressure to build up in
the spray chamber and breach the seal provided by the liquid trap.
Alternatively, glowing particles can fall through the slot into the spray
chamber and ignite the combustible gas mixture inside.
Small deposits in the ends of the burner slot disrupt the laminar gas flow
and allow the flame to burn back into the spray chamber at "Flame Off"
when the gas flow is reduced. Thoroughly clean the burner slot.
The use of a hard object to brush off glowing carbon particles during
flame operation is not recommended because of the increased risk of
knocking one of the particles down the slot.
When using an organic solvent, the thimble of the nebulizer should be set
in a forward or reduced uptake position, to restrict the amount of liquid
fuel that is fed to the flame (refer to the Operation chapter for more
information – Page 67).
The width of the burner slot must not exceed the Table 9. Maximum
allowable burner slot width design specification – see Page 121.
Even a small increase in width can greatly increase the possibility of a
flashback occurring.
Ensure that the spray chamber and liquid trap are kept clean.
If dirty solutions are being analyzed (e.g., engine oils), ensure that the spray
chamber, liquid trap, float and drain tube are regularly cleaned and flushed
with a suitable solvent so that sludge does not build up in the parts.
Ensure that the correct O-rings are used on the burner, nebulizer block and
nebulizer, and that they remain undamaged.
Damage to O-rings in the spray chamber can result in the leakage of gas
which can be ignited by the flame and in turn set fire to the spray
chamber.
Safety Practices and Hazards
29
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