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Subchapter 7. General Industry Safety Orders
Group 16. Control of Hazardous Substances
Article 109. Hazardous Substances and Processes
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§5188. Molten Salt Baths.

(a) Where molten salt baths are used for heat-treating metallic objects.

(1) All objects shall be thoroughly cleaned of oil, grease and dirt, and thoroughly dried of all moisture before being placed in the bath.

(2) Means shall be provided whereby the operator is protected from splashes or spatters of the molten salt while inserting or withdrawing metal objects.

(3) Hoods shall be provided for all baths containing nitrates or cyanides or other baths if fumes or vapors are produced in amounts giving rise to harmful exposure. Such hoods shall be provided with mechanical exhaust ventilation unless sufficient natural draft is produced.

(4) Where the location of the bath is such that there is a possibility of water coming in contact with the molten salt, a hood, shield, or other means shall be provided to preclude such contact.

(5) Workers exposed to spatters or splashes shall be protected as prescribed in Article 10. Clothing should be of wool or other material which does not burn readily.

(6) Baths not protected by hood or shield shall be provided with a removable cover which shall be placed over the bath during temporary shut downs and at end of periods of use.

(b) Nitrate Baths. In addition to the requirements of (a):

(1) No salt containing any cyanide or any organic compound shall be added to a salt bath containing nitrate. Proper warning signs to this effect shall be posted near all such baths.

(2) Nitrate baths shall not be operated at a temperature of greater than 1200 degrees F.

(3) Nitrate baths used to treat aluminum or its alloys shall not be operated at a temperature greater than 1000 degrees F. In such baths if the temperature reaches 1000 degrees F, or if the objects being treated and the bath appear to be beginning an exothermic reaction the operator shall withdraw the metal objects from the bath.

(4) Every nitrate bath over 10 cubic feet in capacity shall be provided with an automatic cut-off safety control which will shut off the source of heat when the temperature reaches the limits set forth in (2) or (3). This control shall be in addition to any regular controls whether they act automatically or manually.

(5) If external heating by gas or oil is used, the combustion chamber shall be arranged so that the sides of the chamber are bathed in hot gasses as uniformly as possible without any flame impinging directly on the containers and so that in case of failure of the container, molten salt will flow to a safe place and so that molten salt cannot drip or spatter into the combustion chamber.

(6) The molten salt container shall be emptied at regular intervals and inspected for deterioration. When inspection shows that deterioration has taken place to such an extent that failure is likely, or that uneven heating of the salt may occur, the container shall be replaced or repaired.

(7) No article shall be allowed to stay in the bottom of the bath. Accumulations of sediment or products of partial decomposition shall be removed regularly, as often as is necessary to prevent uneven heating of the bath. The chemical content of the bath should be checked frequently.

(8) Nitrate shall not be stored in the room with the bath. Storage in a separate building is recommended.

(9) Buildings in which nitrate baths are located should be of construction recommended by the National Board of Fire Underwriters Research Report, No. 2, 1954, for such location. Combustible materials in a room with a bath shall be kept to a minimum.

(10) Magnesium or magnesium alloy shall not be heat-treated in nitrate baths.

(11) When heat is turned off such a bath and before it is allowed to cool, a metal wedge long enough to reach from the bottom of the bath to above the surface shall be inserted to prevent explosion when bath is reheated.

NOTE: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.


1. Renumbering and amendment of Section 5203 to Section 5188 filed 12-10-87; operative 1-9-88 (Register 87, No. 51).

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