🌿 Iron oxides in workplace air — flame AAS

Environment PN-Z-04469

Overview

The edition PN-Z-04469:2025-02 replaced PN-Z-04469:2015-10.

Iron oxides — haematite (Fe₂O₃), magnetite (Fe₃O₄), iron(II) oxide — occur in the air of ore mines, in metallurgical processes and above all in welding. Their inhalation has an irritant action; with continuous exposure they are deposited in the lungs, causing iron pneumoconiosis (siderosis) — the oldest known benign pneumoconiosis — and high concentrations (more than 10 mg Fe/m³) may damage the respiratory tract ("welder's lung"). In the regulation on the maximum admissible concentrations (NDS) and intensities (NDN) iron oxides — calculated as Fe — have admissible values laid down for the inhalable fraction (5 mg/m³) and for the respirable fraction (2.5 mg/m³).

The method employing flame atomic absorption spectrometry was worked out at CIOP-PIB as a revision of the standard PN-79/Z-04066.02, which met neither the requirements of PN-EN 482 (a limit of determination at the level of 1/10 of the NDS) nor the principles of personal sampling of PN-Z-04008-7; that procedure became the basis of the standard PN-Z-04469:2015-10 (the next edition 2025-02). In the 2013 procedure, from which the course described below is taken, the limit of determination for the respirable fraction is 0.35 mg/m³ with an air volume of 720 l, and the measuring range of 0.35–10.4 mg/m³ corresponded to 0.07–2.1 of the NDS value in force at that time (5 mg/m³ for the respirable fraction); where there are other iron compounds in the air the sum of the iron is determined. The more recent CIOP-PIB procedure (2021) determines manganese, nickel and iron in both fractions of the aerosol in a single analytical run — for iron in the range of 0.35–10.42 mg/m³ in the inhalable fraction and 0.17–5.21 mg/m³ in the respirable fraction (720 l of air, 10 ml of solution after mineralisation), i.e. about 0.07–2.08 of the NDS values of 2018. The PKN catalogue card of the PN-Z-04469:2025-02 edition (read on 23.09.2026) gives the same lowest determinable concentrations: 0.35 mg/m³ for the inhalable fraction and 0.17 mg/m³ for the respirable fraction. How the course according to the 2025-02 edition differs from the one described below — WE HAVE NOT ESTABLISHED: we do not have the text of the standard.

Method principle

Course according to the CIOP-PIB procedure of 2013 (the basis of the 2015-10 edition). A known volume of air (up to 720 l) is drawn through a cellulose ester membrane filter with a pore diameter of 0.85 µm placed in the head of a cyclone or in another separator of the respirable fraction (for the inhalable fraction — in a suitable sampler). The filter is mineralised in a beaker with 2 ml of concentrated HNO₃ (65 %) on a hot plate at a temperature of about 140 °C almost to dryness (the operation is repeated twice), 4 ml of 1 mol/l HNO₃ is added, after 30 min it is transferred quantitatively with 0.1 mol/l HNO₃ into a 50 ml flask, and 1 ml of that solution is diluted in a 10 ml flask with the addition of 0.5 ml of lanthanum chloride solution (about 10 % La) as a spectral buffer. Iron is determined in a (lean) air–acetylene flame at a wavelength of 248.3 nm, against a calibration curve of 0.50–15.0 µg/ml prepared on the day of the analysis, the blank from a clean filter being subtracted. The concentration in the air: X = (c − c0)·V1·k/V [mg/m³], where V1 = 50 ml, k = 10, V — the volume of air in litres. The presence of Mn, Ni, Cr and Cu (50–200 µg/ml) does not affect the result.

Applications

• Assessment of occupational exposure to welding fumes and to dusts containing iron oxides — welding shops, grinding shops, metallurgy, ore mines, foundries
• Measurements required by the regulation of the Minister of Health on tests and measurements of harmful agents — comparison with the NDS for the inhalable fraction (5 mg/m³) and for the respirable fraction (2.5 mg/m³)
• Personal sampling in the breathing zone with separation into the fractions of the aerosol
• Determination of the sum of the iron in the aerosol where other iron compounds occur together with the oxides
• Parallel determination of Mn, Ni and Fe from one sample in the CIOP-PIB procedure (2021)

Key parameters

Standard

Standard number

PN-Z-04469:2025-02

Title (PL)

Ochrona czystości powietrza — Oznaczanie tlenków żelaza na stanowiskach pracy metodą płomieniowej absorpcyjnej spektrometrii atomowej

Title (EN)

Air purity protection — Determination of iron oxides at workplaces by flame atomic absorption spectrometry

Step-by-step procedure

1. Sampling

   Calibrate the system for the sampling of the respirable fraction with a flow calibrator for the flow rate required by the manufacturer of the cyclone. In the breathing zone of the worker (the principles of PN-Z-04008-7) draw up to 720 l of air through the filter placed in the head of the cyclone. Where the inhalable fraction is determined take a parallel sample in a sampler of that fraction.

2. Mineralisation

   Place the filter in a 50 ml beaker, add 2 ml of concentrated HNO₃ and heat it on the hot plate (about 140 °C) almost to dryness; repeat twice with 2 ml of the acid. After cooling add 4 ml of 1 mol/l HNO₃ and leave it for about 30 min. Transfer it quantitatively with 5–6 portions of 0.1 mol/l HNO₃ into a 50 ml flask and make up to the mark. In parallel mineralise a clean filter (the blank).

3. Solution for the test

   Into a 10 ml flask transfer 1 ml of the solution after the mineralisation, add 0.5 ml of lanthanum chloride solution and make up with 0.1 mol/l HNO₃. At concentrations outside the range change the dilution factor, retaining the addition of lanthanum.

4. Calibration curve

   On the day of the analysis prepare the working solutions of 0.50; 1.50; 5.00; 10.0 and 15.0 µg/ml Fe (0.5 ml of lanthanum chloride per 10 ml) and a zero sample. Make three measurements of the absorbance of each solution at 248.3 nm in a lean air–acetylene flame, zeroing the spectrometer with 0.1 mol/l HNO₃; prepare the curve or use the automatic calibration of the instrument.

5. Measurement and calculation

   Measure the absorbance of the solution for the test and of the blank under the same conditions, read the concentrations c and c0 from the curve. Calculate X = (c − c0)·V1·k/V in mg/m³ (V1 = 50 ml, k = 10, V — the volume of air in l).

6. Check of the effectiveness of the mineralisation

   Onto six filters apply 600 µl each of the 10 mg/ml Fe solution, dry them until the following day, mineralise them as the samples and compare them with comparison solutions prepared without mineralisation; the factor wm = (Cd − Co)/Cp should be 1.00 ± 0.05 — otherwise change the manner of the mineralisation.

7. Assessment of the exposure

   Determine the index of exposure for the working shift and compare it with the NDS appropriate to the fraction (5 mg/m³ inhalable, 2.5 mg/m³ respirable).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Carry out all the operations with concentrated nitric acid in protective clothing and goggles and under an efficiently working fume cupboard — the hot mineralisation evolves nitrogen oxides
• Acetylene: the gas installation and the burner in accordance with the instructions for the spectrometer; check of leak-tightness, protection against flash-back of the flame
• Collect the residues of the solutions of the reagents and of the standards in marked containers and hand them over to authorised firms for disposal

Frequently asked questions