Introduction to Hydrogen Chloride (HCl)

Hydrogen Chloride (HCl) is a colorless gas at room temperature and is used in many applications in the technology and chemical industry, including cleaning, pickling, electroplating metals, tanning leather, and refining and producing a wide variety of products. Most Hydrogen Chloride is used in the production of hydrochloric acid. Due to its great solubility, this hazardous gas forms hydrochloric acid on contact with moist conditions, ranging from atmospheric humidity to water found in body tissue. It is also an important reagent in other industry chemical transformations, such as hydrochlorination of rubber and production of vinyl and alkyl chlorides.

Hydrogen Chloride has an irritating, pungent odor. Any equipment handling Hydrogen Chloride gas must be checked on a routine basis. The gas requires the use of specialized materials on all wetted parts of the flow path, as it will interact with or corrode numerous materials hydrochloric acid alone will not such as stainless and regular polymers. Exposure risk for the general population is minimal, but personnel working in occupations in which Hydrogen Chloride is used have a high risk of exposure and must follow proper safety and detection methods.

Health Hazards

When present in high concentrations, Hydrogen Chloride may produce these symptoms:

  • Coughing
  • Choking
  • Eye irritation (liquid contact)
  • Nose, throat, respiratory inflammation
  • Pulmonary edema (excess fluid in lung tissue)
  • Circulation system failure
  • Death

Exposure Limits

When researching HCl gas detection solutions, facility managers should be aware of the following HCl exposure limits:

Exposure Limits Agency
5 ppm ceiling OSHA PEL (General Industry)
5 ppm ceiling OSHA PEL (Construction Industry)
5 ppm ceiling OSHA PEL (Maritime)
2 ppm TWA ACGIH TLV
5 ppm TWA NIOSH REL
50 ppm NIOSH IDLH

Technology for HCl Gas Detection

Electrochemical Sensors

Electrochemical sensors are fuel cell-like devices consisting of an anode, cathode, and electrolyte. The components of the cell are selected so that a subject gas, allowed to diffuse into the cell, will cause a chemical reaction and generate a current. The cells are diffusion-limited, meaning that the rate of the gas entering the cell is solely dependent on the gas concentration. The current generated is proportional to the rate of consumption of the subject gas in the cell.

Learn more about the advantages of using Sierra Monitor's electrochemical gas sensor modules »