🌿 Hydrogen chloride in workplace air — turbidimetric method, PN-Z-04450

Environment PN-Z-04450

Overview

WHAT THIS STANDARD DESCRIBES. The scope from the PKN catalogue card, quoted in full: "W niniejszej normie podano metodę oznaczania chlorowodoru (nr CAS: 7647-01-0) w powietrzu na stanowiskach pracy z zastosowaniem metody turbidymetrycznej z pobieraniem próbek na filtry. Metodę stosuje się podczas kontroli warunków sanitarnohigienicznych. Metody nie stosuje się w obecności w badanym powietrzu: chloru, bromu, bromowodoru, jodu, siarczków i siarkowodoru. Najmniejsze stężenie chlorowodoru, jakie można oznaczyć w warunkach pobierania próbek powietrza i wykonywania oznaczania opisanych w normie, wynosi 0,5 mg/m3" [This standard specifies a method for determining hydrogen chloride (CAS No.: 7647-01-0) in workplace air using the turbidimetric method with sampling on filters. The method is used when monitoring sanitary and hygienic conditions. The method is not used when the air under test contains chlorine, bromine, hydrogen bromide, iodine, sulphides or hydrogen sulphide. The lowest concentration of hydrogen chloride that can be determined under the conditions of air sampling and determination described in the standard is 0.5 mg/m3]. The standard was published on 1 August 2014 in a Polish-language version, has eight pages and is maintained by KT 159. The card has no "Replaces" field — it is therefore a document without a predecessor in the PN collection. The card has neither a "Withdrawn" header nor a "Withdrawal date" row (checked on 23.09.2026).

SIX EXCLUDING SUBSTANCES — A LIMITATION MORE IMPORTANT THAN THE LIMIT OF QUANTIFICATION. The standard states explicitly that the method IS NOT USED in the presence of chlorine, bromine, hydrogen bromide, iodine, sulphides and hydrogen sulphide. The mechanism is chemical: the turbidimetric determination consists in precipitating silver chloride and measuring the turbidity, and each of the listed agents either itself forms a precipitate with silver ions (bromine, iodine, sulphides) or oxidises the chloride ions and changes the result (chlorine, hydrogen sulphide). **And here is the practical point: three of these six substances occur at THE SAME workplaces as hydrogen chloride.** Pickling of metals with hydrochloric acid containing admixtures, production and packaging of disinfectants, industrial wastewater treatment plants — everywhere there, chlorine or hydrogen sulphide is often present next to HCl. A laboratory that has this standard in its scope must therefore establish the composition of the air at the workplace for every order, and not merely perform the determination.

A LIMIT OF QUANTIFICATION EXACTLY AT THE THRESHOLD — AND WHAT FOLLOWS FROM IT. The limit value for hydrogen chloride is **NDS 5 mg/m³ and NDSCh 10 mg/m³** (item 119 of the list in the wording given by the regulation of 26 March 2026, Journal of Laws 2026 item 447). The lowest determinable concentration is 0.5 mg/m³, i.e. **exactly one tenth** of the limit value. PN-EN 482 requires a measurement procedure to cover the range from one tenth to twice the limit value — this method meets the requirement EXACTLY AT THE BOUNDARY, without any margin. In practice this means that any deterioration of the conditions — shorter sampling, a smaller sample volume, a higher background — takes the method outside the requirement. For comparison: for potassium hydroxide (PN-Z-04436, a separate entry in this database) the margin is one twelfth, and for sodium hydroxide one twentieth.

NO TRANSITIONAL PROVISION — CHECKED ON THE TEXT OF THE ACT. § 2 of the amending regulation lists thirteen items for which the values from the annex apply later or at a different level. **Hydrogen chloride is not among them**, so the values of 5 and 10 mg/m³ apply directly. We give this negative result because without it the reader does not know whether the check was made.

SCALE OF CITATIONS (reading of 23.09.2026, copy of the database of accreditation scopes). Matching by the BEGINNING of the notation, i.e. the way the "Laboratories" tab searches: 18 entries at 17 laboratories; across all forms of the core "04450" — the same. Only TWO forms of notation, the balance of occurrences agrees: "PN-Z-04450:2014-08" 16 times and "PN-Z-04450:2014" without the month 2. The notation is clean — no distortion of the PN element, no addition, no number of an own procedure. The ratio of entries to laboratories is 1.1.

TWO NOTATIONS WITHOUT THE MONTH ARE NOT AN ERROR, BUT AN OLDER CONVENTION. The designation "PN-Z-04450:2014" omits the month element that PKN introduced into the numbering of standards published after 2010. Matching by the beginning of the notation covers both notations, because they differ only at the eleventh character — but if the key of this entry read "PN-Z-04450:2014-08", these two laboratories would drop out of the tab. This is the same mechanism as with a distorted prefix, only at the opposite end of the designation: **the key must not be longer than the shortest notation it is meant to cover**.

Method principle

Hydrogen chloride is retained on a filter while a known volume of air from the workplace is drawn through it. The chloride ions are washed out of the filter, and silver chloride is precipitated in the resulting solution by adding silver ions. The resulting suspension is measured turbidimetrically — the intensity of the scattered light is proportional to the amount of precipitate, and therefore to the chloride content. The concentration of hydrogen chloride in air is calculated from the chloride content in the solution and the volume of air drawn. The method therefore measures CHLORIDE IONS, not the HCl molecule — which is why any substance that forms a precipitate with silver ions or changes the oxidation state of the chlorides falsifies the result, and why the standard lists six such substances as excluding.

Applications

• Periodic measurements of occupational exposure required by the regulation of the Minister of Health on tests and measurements of agents harmful to health in the working environment
• Pickling plants and workplaces where metals are treated with hydrochloric acid
• Production and packaging of household chemicals and disinfectants
• Checking the effectiveness of local exhaust ventilation at hydrochloric acid tanks — provided that the presence of chlorine has been ruled out

Key parameters

Standard

Standard number

PN-Z-04450:2014-08 (wersja polska)

Title (PL)

Ochrona czystości powietrza -- Oznaczanie chlorowodoru na stanowiskach pracy metodą turbidymetryczną z pobieraniem próbek na filtry

Title (EN)

Air purity protection — Determination of hydrogen chloride at workplaces by turbidimetric method with sampling on filters

Step-by-step procedure

1. Checking the conditions at the workplace

   Establish that chlorine, bromine, hydrogen bromide, iodine, sulphides and hydrogen sulphide do not occur in the air. If any of them is present, the method MUST NOT be used; another procedure must be chosen.

2. Sampling

   Draw a known volume of air from the worker's breathing zone through the filter.

3. Washing out the chlorides

   Wash the chloride ions out of the filter into a solution of known volume.

4. Precipitation and measurement

   Add silver ions, wait for the time provided for in the procedure and measure the turbidity of the suspension.

5. Calculation

   Read the chloride content from the calibration curve and calculate the concentration of hydrogen chloride in air from the volume of air drawn.

6. Reference to the limit values

   Compare the exposure index for the work shift with the NDS of 5 mg/m³, and the results of short-term measurements with the NDSCh of 10 mg/m³. Record in the report on what basis the presence of interfering substances was ruled out.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Hydrogen chloride is corrosive to the respiratory tract and eyes — carry out sampling wearing the personal protective equipment appropriate to the workplace
• Silver nitrate(V) stains skin and fabrics; work in gloves and store the reagent in dark glass containers
• If the presence of chlorine or hydrogen sulphide at the workplace is suspected, measurement by this method is not permissible, and these agents themselves require a separate exposure assessment

Frequently asked questions