Oxidising Chemicals
Acids & Corrosives · Acids & Corrosives overview
Oxidising chemicals — nitric acid, chromic acid, hydrogen peroxide, peracetic acid, hypochlorite, permanganate, persulphate and the strong oxidising halogens — are central to metal finishing, water treatment, disinfection, paper and pulp bleaching, and specialty chemical manufacture. They release reactive, corrosive and sometimes toxic species when they meet metals, organics or other reducers, and their airborne exposure is controlled under the Control of Substances Hazardous to Health (COSHH) Regulations 2002.
Where oxidising chemicals are used
Oxidisers are present across UK industry in both bulk and small-scale use. The main workplace settings are metal passivation and brightening, electropolishing, chromic and decorative chrome plating, peroxide bleaching of pulp and textile, peracetic and hypochlorite disinfection in food and water, and persulphate microetching in electronics.
- Nitric and chromic acid passivation, bright-dipping and electropolishing.
- Chromic and decorative chrome plating baths.
- Hydrogen peroxide bleaching in pulp, paper and textile finishing.
- Peracetic acid and hypochlorite disinfection in food, brewing and water treatment.
- Persulphate microetching in printed-circuit and metal finishing shops.
- Permanganate cleaning, oxidation and water treatment.
Why oxidising chemical exposure matters
Oxidising chemicals damage tissue both directly and through the reactive products they release. Chromic acid mist (chromium VI) is a recognised respiratory carcinogen with a low EH40 limit. Hydrogen peroxide and peracetic acid vapours are sharp respiratory irritants and have short-term EH40 limits set for the brief, intense peaks generated during dosing and decanting. Hypochlorite mixed inadvertently with acid releases chlorine. Persulphate is a recognised occupational sensitiser implicated in hairdresser and electronics-worker asthma.
Oxidisers also raise fire and explosion risk by accelerating combustion of organic materials — but the occupational hygiene focus is the airborne corrosive and reactive species their use generates around operators.
Monitoring airborne oxidising substances
Each oxidiser is sampled by a method matched to its chemistry. Chromium VI is sampled on a treated filter and analysed by a sensitive colorimetric or IC method against the strict EH40 limit. Hydrogen peroxide and peracetic acid are sampled on impregnated filters or sorbent media. Hypochlorite exposure is sampled as chlorine in air. Sampling strategy follows BS EN 689, with explicit attention to short-term limits during dosing, decanting and equipment cleaning.
Direct-reading instruments — peroxide and chlorine sensors — support tank-side diagnostics and incident response but do not substitute for laboratory-analysed personal samples for the formal COSHH judgement.
Controlling oxidising chemical exposure
The COSHH hierarchy applies. Substitute where possible — citric passivation for nitric, lower-strength peroxide formulations, sealed CIP for hypochlorite. Where the oxidiser must remain, enclose dosing skids and reactors, lid storage and process tanks, provide LEV designed for corrosive and oxidising duty, and scrub the discharge. Acid- and oxidiser-resistant materials are essential — many fluoropolymer linings and FRP grades are specified for oxidiser duty.
Procedural controls — segregate oxidisers from organics and reducers, control dosing temperature and sequence, and provide RPE and PPE rated for the worst credible release — complete the package.
When to review oxidising chemical risk
Review on a change of oxidiser, concentration, dosing skid or sequence; on changes to organic load or substrate; following spills, fires or near-misses; on operator symptoms or sensitisation reports; after enforcement or insurer audit; and at a defined refresh interval. Chromic and persulphate processes warrant shorter review cycles and more intensive monitoring than general oxidisers.
Frequently asked questions
Why does chromic acid get singled out?
Chromic acid mist contains chromium VI, an EH40-listed Category 1 carcinogen with a very low limit. It requires dedicated sampling, fume-suppressed baths, well-maintained acid LEV and frequent review.
Are persulphates an occupational asthma risk?
Yes. Persulphate salts are recognised respiratory sensitisers, with documented occupational asthma among hairdressers and electronics-finishing operators. Dust and aerosol containment and personal sampling are essential where they are used.
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