🌿 Sulphuric(VI) acid and sulphur trioxide (in the standard "trójtlenek") in workplace air — membrane filter, mineralisation, reaction with barium chloride in ethylene glycol, turbidimetric measurement; determinability according to the standard 0.20 mg/m³ of sulphuric acid and 0.17 mg/m³ of sulphur trioxide, MAC (NDS) for sulphuric acid 0.05 mg/m³ (thoracic fraction), NDS for sulphur trioxide 1 mg/m³; PN-Z-04056-02:1991 (withdrawn 17-10-2011)

Environment PN-Z-04056-02

Overview

WHAT THE STANDARD COVERS. Scope from the PKN card, in full: "The method consists in collecting the aerosol of sulphuric acid and sulphur trioxide on a membrane filter, mineralising the filter, dissolving the residue in water and causing a reaction with barium chloride in ethylene glycol. The turbidity of the suspension obtained is measured turbidimetrically. The determinability of the method is 0.20 mg of sulphuric acid and 0.17 mg of sulphur trioxide in 1 cubic metre of air" (our translation; on the card without a full stop at the end). We did not have the text of the standard (2 pages). The CIOP index of methods from 2000–2017 lists "Kwas siarkowy – frakcja torakalna nr 1(71) 2012"; we did not read the article and give nothing from it.

NDS VALUES (list in the annex to the regulation of 26 March 2026, Journal of Laws 2026 item 447). Item 349: "Sulphuric(VI) acid [7664-93-9] – thoracic fraction" — NDS 0.05 mg/m³, no NDSCh; the thoracic fraction is defined according to PN-EN 481 (footnote 19 of the list: the aerosol fraction "penetrating into the respiratory tract within the chest"). Item 560: "Sulphur trioxide" — NDS 1 mg/m³, NDSCh 3 mg/m³. The determinability of sulphuric acid according to the card, 0.20 mg/m³, is four times the NDS; the determinability of sulphur trioxide, 0.17 mg/m³, is 17 % of its NDS.

STATUS (card as of 04.10.2026). The card of PN-Z-04056-02:1991 (Polish version) has the heading "Withdrawn": published 31-05-1991, withdrawal date 17-10-2011, 2 pages, price group A, Health, Environment and Medicine Sector, KT 159 Chemical and Dust Hazards in the Working Environment, ICS 13.040.30, "Replaces PN-Z-04056-02:1971"; the card does not name a replacing standard. The PKN search for "PN-Z-04056" (04.10.2026) shows six items, all labelled "Withdrawn": PN-Z-04056:1959 (rapid method for sulphuric acid mist), parts 01 and 02 of 1971 and 1991, and part 03:1979 (titrimetric method). The first result pages for "kwasu siarkowego" and "tritlenku siarki" (50 items each) contain no current standard for sulphuric acid or sulphur trioxide at workplaces.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data load up to 17.09.2026, read on 04.10.2026). The number 04056-02 (with a hyphen, full stop or slash before the part number) appears in 4 records at 4 laboratories; in the current PCA documents (read on 03.10.2026; issues from 04.02.2026 to 07.05.2026 — all issued after the withdrawal of the standard) — in 4 rows at the same laboratories; a search of all PCA documents downloaded from the BIP found no laboratories outside the database copy; no item is suspended, and no document repeats pages. The form "PN-91/Z-04056/02" — AB 802 and AB 964; "PN-91/Z-04056.02 z wyłączeniem pkt. 7" — AB 1004; "PN-Z-04056-02:1991" — AB 877. The "Laboratories" tab: "PN-91/Z-04056/02" shows 2 laboratories, "PN-91/Z-04056.02" — 1, "PN-Z-04056-02" — 1, 4 in total, the same in the copy and on the labcoda.pl production server (tab queries of 04.10.2026).

WHAT THE LABORATORIES TEST (database copy and PCA documents). Working environment: AB 802 — concentration of sulphur trioxide, 0.092–7.0 mg/m³, turbidimetric method; AB 964 — concentration of sulphur trioxide, 0.1–13.8 mg/m³, spectrophotometric method. General environment and waste gases: AB 877 — air and waste gas samples collected on filters, content of sulphuric acid 0.303–50.0 mg per sample and of sulphur trioxide 0.250–41.50 mg per sample, turbidimetric method; AB 1004 — waste gases, concentration of sulphuric(VI) acid and sulphur trioxide 0.1–20 mg/m³ (0.1–10 mg per sample), turbidimetric method, "excluding point 7". None of the four laboratories determines sulphuric acid at workplaces according to this standard.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — sensitivity against the NDS for sulphuric acid: the determinability from the card, 0.20 mg/m³, is four times higher than the NDS of 0.05 mg/m³ — the method as worded on the card cannot assess exposure to sulphuric acid at the NDS level; the laboratories working at workplaces have only sulphur trioxide in their scopes. Second — fraction: the NDS for sulphuric acid concerns the thoracic fraction according to PN-EN 481, while the card speaks of a membrane filter without a fraction sampler. Third — object: AB 877 and AB 1004 apply the "at workplaces" standard to waste gases, i.e. an emission measurement, for which the NDS is not a reference value. Fourth — technique: the card describes a turbidimetric measurement, while AB 964 gives a spectrophotometric method. Fifth — status: the standard has been withdrawn since 17-10-2011, and the reviewed PKN search results (term "PN-Z-04056" and the first 50 items for the two substance terms) contain no current standard; 4 laboratories have it in scopes issued in 2026. Sixth — AB 1004 excludes point 7 of the standard, whose content we do not know.

WHAT WE DO NOT GIVE. We did not have the text of the standard — we do not give the volume or flow rate of air sampling, the type of filter, the mineralisation conditions, the reagent concentrations, the wavelength or calculations; we do not describe how the standard distinguishes sulphuric acid from sulphur trioxide. We do not claim that another standard has replaced PN-Z-04056-02:1991 — PKN names none.

Method principle

The aerosol of sulphuric acid and sulphur trioxide from workplace air is collected on a membrane filter, the filter is mineralised, the residue dissolved in water and reacted with barium chloride in ethylene glycol, and the turbidity of the suspension is measured turbidimetrically (PKN card). Determinability according to the card — 0.20 mg/m³ of sulphuric acid (above the NDS of 0.05 mg/m³) and 0.17 mg/m³ of sulphur trioxide (NDS 1 mg/m³). The standard is withdrawn (17-10-2011); WE DO NOT GIVE details — we did not have the text of the standard.

Applications

• Workplace air — sulphur trioxide (AB 802, AB 964); waste gases and air — sulphuric acid and sulphur trioxide (AB 877, AB 1004); despite the withdrawal of the standard
• Assessment of occupational exposure to sulphur trioxide against the NDS of 1 mg/m³ and the NDSCh of 3 mg/m³ (Journal of Laws 2026 item 447, item 560); for sulphuric acid (item 349, NDS 0.05 mg/m³) the determinability from the card is too high

Key parameters

Standard

Standard number

PN-Z-04056-02:1991

Title (PL)

Ochrona czystości powietrza — Badania zawartości kwasu siarkowego i trójtlenku siarki — Oznaczanie kwasu siarkowego i trójtlenku siarki na stanowiskach pracy metodą turbidymetryczną

Title (EN)

Air purity protection — Tests for sulphuric acid and sulphur trioxide content — Determination of sulphuric acid and sulphur trioxide at workplaces by turbidimetric method

Step-by-step procedure

1. Status

   PN-Z-04056-02:1991 withdrawn 17-10-2011, with no successor named (card as of 04.10.2026).

2. Sampling and mineralisation

   Aerosol on a membrane filter, mineralisation of the filter, dissolution of the residue in water (PKN card); WE DO NOT GIVE the conditions.

3. Reaction and measurement

   Reaction with barium chloride in ethylene glycol, turbidimetric measurement of the turbidity (PKN card).

4. Result and assessment

   Concentration in mg/m³; sulphur trioxide against the NDS of 1 mg/m³ and the NDSCh of 3 mg/m³; for sulphuric acid (NDS 0.05 mg/m³, thoracic fraction) the determinability from the card of 0.20 mg/m³ is too high.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Mineralisation and acid aerosols — work in a fume hood, chemical laboratory safety rules
• TECHNICAL NOTE: the determinability of sulphuric acid from the card (0.20 mg/m³) exceeds the NDS of 0.05 mg/m³; two laboratories apply the standard to waste gases

Frequently asked questions