Corrosive Chemicals
Acids & Corrosives · Acids & Corrosives overview
Corrosive chemicals — strong acids, strong alkalis and reactive halogens — are used across UK metal finishing, chemical processing, water treatment, food manufacturing, cleaning and laboratory work. When they are heated, agitated, electrolysed or sprayed they release corrosive mists, fumes and vapours that injure the eyes, skin and respiratory tract. Airborne exposure to corrosive chemicals is controlled under the Control of Substances Hazardous to Health (COSHH) Regulations 2002 and read against the Workplace Exposure Limits in HSE EH40.
What counts as a corrosive chemical
A corrosive chemical is one that destroys living tissue and many engineering materials on contact. In UK workplaces the main groups are: strong inorganic acids (sulphuric, hydrochloric, nitric, hydrofluoric, phosphoric, chromic); strong organic acids (formic, acetic, peracetic, methanesulphonic); strong alkalis (sodium and potassium hydroxide, ammonia); reactive halogens and halides (chlorine, bromine, hypochlorite); and certain specialty oxidisers used in cleaning and surface treatment.
Each behaves differently in air — sulphuric forms a non-volatile mist, hydrochloric and nitric release both mist and gas, caustic forms an alkaline aerosol, and chlorine and ammonia are predominantly gaseous. A single COSHH approach for all corrosives under-controls the worst and over-controls the rest.
How corrosive chemicals reach the operator
Airborne exposure happens through the same handful of mechanisms: open or partially enclosed tanks, electrolytic gassing, high-pressure or spray dosing, splashing during loading and dragout, decanting and dosing from bulk containers, leakage from pumps and seals, and chemical reaction with substrate metals. Personal exposure is concentrated at the tank rim, sample point, pump skid and rectifier station.
- Tank loading, unloading, dragout and rack jigging.
- Acid and caustic dosing into reactors, scrubbers and CIP systems.
- Bulk transfer from IBC, tanker or drum into process plant.
- Maintenance — pump and seal change, filter change, breakdown response.
- Sampling, dipping and laboratory analysis.
- Spray and high-pressure cleaning of process equipment.
Why corrosive exposure matters
Corrosive aerosols and vapours injure tissue on contact. Acute effects include burning of the eyes, nose and throat, chemical pneumonitis at high concentration, and serious skin burns where the aerosol settles on bare skin. Chronic low-level exposure is associated with dental erosion, chronic upper-airway irritation, occupational asthma in some workers, and — for strong inorganic acid mists — the IARC Category 1 association with laryngeal cancer.
Most of the corrosive substances have their own EH40 WEL, often including a 15-minute short-term limit. Demonstrating control means comparing measured personal exposure against the correct substance-specific limit, not a generic value.
Monitoring corrosive chemical exposure
Each substance is sampled by a validated MDHS-equivalent method appropriate to its chemistry. Acid mists are collected on treated filters or impingers and analysed by ion chromatography for the relevant anion. Caustic aerosols are analysed for sodium or potassium ion. Chlorine, hydrogen chloride, hydrogen fluoride and ammonia have their own sorbent-tube and diffusive sampler approaches. Sampling strategy follows BS EN 689.
Direct-reading detector tubes and electrochemical sensors support walk-through surveys, LEV commissioning and incident response, but the COSHH judgement against the WEL is built on laboratory-analysed personal samples.
Controlling corrosive chemicals
The COSHH hierarchy applies to corrosives as to any other hazardous substance: substitute to a less hazardous chemistry or concentration where the process allows; cover, enclose and minimise free surface; provide LEV designed for corrosive duty with acid- and alkali-resistant materials; scrub the discharge where airborne corrosives would otherwise be released to the workplace neighbourhood; and use RPE and chemical PPE for tasks where engineering control alone cannot reach the limit.
LEV for corrosive duty must be designed and maintained as a corrosion-resistant system — polypropylene or FRP ducting, acid- or alkali-rated fans, suitable gaskets and joints, with Thorough Examination and Test at least every 14 months under COSHH Reg 9.
When to review corrosive chemical exposure
Review the assessment on a change of substance, concentration, temperature, throughput or LEV; on incidents and near-misses; on operator symptoms; following enforcement or insurer review; and at a defined two- to three-year refresh interval. Specific high-hazard substances such as chromic acid, hydrofluoric acid and chlorine warrant shorter review cycles and more intensive monitoring.
Frequently asked questions
Is one WEL used for all corrosive chemicals?
No. Each substance has its own EH40 limit, often with both an 8-hour TWA and a 15-minute short-term limit. Reading exposure against a generic corrosive value will mis-classify the COSHH judgement.
Are corrosives only an inhalation hazard?
No. Skin and eye contact with corrosive mists can cause serious chemical burns. PPE, splash protection and safety showers are essential alongside inhalation controls.
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