Even a small concentration of hydrochloric acid in the air irritates the membranes of the respiratory tract making it easily detectable in amounts below the Threshold Limit Value of five parts per million. One to five parts per million can be detected by smell, while five to ten parts become disagreeable.
In addition hydrochloric acid mixed with sodium cyanide liberates HCN gas. This is extremely dangerous (read the cyanide safety section). Contact of hydrochloric acid with any cyanide containing solutions must be avoided.
Personal protective equipment is not an adequate substitute for good safe working conditions, adequate ventilation or intelligent conduct on the part of employees working with hydrochloric acid. In many instances, however, it is the only means of protecting the worker, particularly in emergency situations.
Under conditions which are sufficiently hazardous to require personal protective equipment, its use should be supervised and the type of protective equipment selected should be capable of control over any potential hazards.
Hydrochloric acid can emit gas, hydrogen chloride, which has a highly corrosive action upon the skin and mucous membranes due to the rapid absorption of the gas on these surfaces, forming hydrochloric acid and heat. Either the liquid or gas will therefore cause burns, if in contact with any part of the body. If taken by mouth, the acid may injure the gastrointestinal tracts, whereas breathing the anhydrous vapors may injure the respiratory tract.
Either the gas or the liquid are particularly damaging to the eyes and prompt removal with copious quantities of water is essential. The vapor has such a sharp and penetrating odor, that the inhalation of seriously toxic quantities is unlikely, unless the victim is trapped in such a location that escape from the vapor is impossible.
Employees should be instructed to avoid contact with hydrochloric acid at all times. In instances where contact is unavoidable, adequate personal protective equipment as described above should be used.
The importance of emergency showering and prompt removal of contaminated clothing following contact with liquid acid or concentrated vapors, must be emphasized. Adequate emergency showers and wash-up facilities should be available in areas where hydrochloric acid is used. Eye wash fountains should be placed in accessible locations, and employees should be instructed in their use. Employees should be instructed to make a prompt report of any suspected burns or exposures, or any irritated conditions of the eyes, nose or throat.
The hydrochloric acid system is only to be used to descale the drum filter cloths or the clarifier leaves. Extreme care must be taken when using hydrochloric acid and all users should be familiar with the potential hazards.
The acid wash system in this plant is portable and consists of a small cart which carries the drum of inhibited muriatic acid (34% hydrochloric acid), the acid mixing tank and the acid feed pump.
The system must be wheeled into place before a batch of acid can be prepared. Once in place, the mix tank can be filled with fresh water (DO NOT USE RECLAIM WATER OR BARREN SOLUTION TO MIX A BATCH OF HYDROCHLORIC ACID) followed by the desired amount Of acid. ALWAYS ADD ACID TO WATER, NOT WATER TO ACID. When the desired acid solution (3% HC1 v/v) is thoroughly mixed, and the feed pump discharge line connected to the permanent drum filter acid wash lines, the feed pump can be started and acid washing of a drum filter can begin. The flow of acid onto the drum filter is locally controlled with a rotometer.