This writer has heard of many accidents that occur in heat-treatment shops on an international basis with the use of low-temperature (nitrate) heat-treatment salts. The safety aspect of using heat-treatment salts cannot be overemphasized.
Salt is a wonderful method of heat treatment, particularly for the aspect of temperature uniformity. It cannot be more strongly emphasized that when using any heat-treatment salts (low or high temperature) that the utmost of care be taken not only by the heat-treatment associate but also by management in terms of lectures on the use of the salts, handling the salts and safety.
Nitrate salts are generally comprised of a mixture of potassium nitrate and sodium nitrite. Both of these salts are oxygen suppliers, and one often finds them being used occasionally in the mixture of gunpowder. So, extreme care needs to be applied when using not only the nitrate salts but any heat-treatment salt.
If the salt bath is in need of repair and it necessitates a person going inside of the salt bath (empty, of course), the event should and MUST be considered as CONFINED-SPACE ENTRY. The appropriate meeting of all involved in the repair of the salt bath must understand each other’s function and the potential dangers of confined-space entry.
The last statement applies not only to heat-treatment salt baths. Any furnace that requires an entry into the process chamber or quench tank must be considered confined-space entry, and each person should sign off that they understand the confined-space entry requirements.
When handling the salts (nitrate or otherwise), one should wear the appropriate safety clothing. That safety clothing will be comprised of:
- A fire-resistant insulated long-sleeved jacket
- Fire-resistant insulated over-trousers
- Long-sleeved insulated gloves
- Shoe spats to prevent burning of the feet with liquid salt splashes
- Safety goggles for eye protection
- Safety full-face and head-face shield
- Head-protection helmet
We will conclude this discussion next time in part 2.