What Are Corrosive Substances? Class 8, pH, Risks & Safety

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Corrosive substances are chemicals that destroy living tissue and degrade materials by chemical action. Beyond strong acids and alkalis, some salts and gases are corrosive too. They can burn skin and eyes, damage airways if inhaled, and eat through metals. In dangerous goods terms they’re Class 8.

This guide explains what qualifies as corrosive, how Class 8 is applied under ADR, IMDG and IATA, and why pH and corrosion‑rate tests matter. We’ll compare acids and bases, give common examples, outline health, property and environmental risks, show how to read labels and SDSs, and share practical storage, handling, mixing and emergency steps, including hydrofluoric acid considerations.

How corrosives are defined and classified

OSHA defines a corrosive substance as a chemical that causes visible destruction or irreversible change in living tissue at the site of contact. In transport, these substances are assigned to Hazard Class 8. Corrosives include acids and bases and can be liquids, solids or gases; the defining test is their ability to cause full‑thickness skin destruction within a specified time or severe tissue damage on contact. Typical examples include sulfuric acid, sodium hydroxide, bromine and concentrated hydrogen peroxide.

Understanding class 8 and where it applies

Class 8 is the UN dangerous goods transport class for corrosive substances. It applies whenever corrosives are carried by road (ADR), sea (IMDG Code), air (IATA/ICAO) or rail (RID). The class is based on a material’s ability to cause full‑thickness skin destruction within a specified time and includes liquids and solids. Assigning Class 8 triggers mode‑specific requirements for packaging, labelling, documentation, placarding, segregation from incompatibles, and emergency response information. It is a shipping classification; workplace hazard systems such as OSHA run alongside it.

pH, corrosion rate and other criteria for classification

pH is a quick screening tool. Many safety programmes flag liquids with pH ≤4 or ≥9 as corrosive, but pH alone does not set Class 8; buffering, non‑aqueous systems and concentration can change the outcome. For transport, decisive criterion is whether the substance causes full‑thickness skin destruction within a set time, supported by test data and expert judgement.

  • Skin corrosion data: demonstrated tissue destruction in tests drives the class and severity.
  • Corrosion to metals: corrosion rate on steel or aluminium signals risks to packaging and vehicles and informs compatibility.

Acids versus bases: similarities, differences and examples

Both acids and bases are corrosive: they destroy tissue and can attack metals; mixed they neutralise vigorously, often releasing heat, so must be segregated. Acids have pH < 7, turn blue litmus red, e.g. sulfuric (H2SO4) and hydrochloric (HCl). Bases have pH > 7, turn red litmus blue, e.g. sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)2).

Common examples in industry and at home

Across industry, common corrosive substances include sulfuric, hydrochloric and nitric acids; sodium hydroxide (caustic soda) and calcium hydroxide; bromine; high‑strength hydrogen peroxide; and specialist acids such as hydrofluoric and perchloric acid. At home you’ll encounter corrosives in drain and oven cleaners, toilet bowl cleaners, and car batteries (battery acid). These examples span liquids and solids.

Health hazards: routes of exposure and effects

Corrosive substances harm by skin and eye contact, inhalation of vapours, mists or dusts, and ingestion. Contact causes immediate chemical burns; solids and their dust can react with moisture on skin or in airways. Eye splashes can rapidly damage the cornea and lead to permanent vision loss. Inhaling corrosive atmospheres irritates or burns the nose, throat and lungs. Swallowing causes burns from mouth to stomach. Some, such as hydrofluoric acid, add delayed systemic toxicity and require specific antidote measures.

Property and environmental risks

Beyond personal harm, corrosives attack assets and the environment. Leaks can pit steel and aluminium, degrade concrete, and compromise tanks, pipes, vehicles and packaging—causing leaks or failure. Contact with metals can release flammable hydrogen; neutralisation generates heat. Spills contaminate soil and waterways, and incompatible mixes can liberate toxic or flammable vapours.

How to identify corrosives on labels and SDSs

To identify corrosives, check labels and the Safety Data Sheet (SDS). For transport, look for the Class 8 ‘Corrosive’ label and UN number; workplace labels and the SDS set out the classification and controls, and confirm if a product is corrosive.

  • Corrosion pictogram: the standard symbol used for corrosive hazards on labels and packages.
  • SDS essentials: classification, PPE, storage/segregation, incompatibilities, spill response and first aid.
  • Transport identifiers: Class 8 mark on packages, plus proper shipping name and UN number.

Storage and segregation basics you must follow

Store Class 8 corrosives to prevent leaks, reactions and exposure. Keep acids separate from bases and other incompatibles to avoid heat and hazardous vapours. Use corrosive‑rated cabinets with secondary containment, and keep containers below eye level near an eyewash and emergency shower.

  • Segregate: store acids and bases in separate cabinets.
  • Contain: use corrosion‑resistant trays/bunds for secondary containment.
  • Position: never above eye level; heavy bottles low.
  • Readiness: keep spill kits and neutralisers—CaCO3 for acids, citric acid for bases.

Handling and PPE essentials for corrosives

Handle Class 8 substances with controls that prevent splashes, inhalation and skin contact. Work in a fume hood, keep an eyewash and emergency shower immediately available, and check the SDS for required PPE and incompatibilities before you start.

  • Goggles and face shield: Wear chemical splash goggles; add a face shield for high‑splash tasks—never a shield alone.
  • Gloves: Choose compatible chemical‑resistant gloves (e.g., butyl); inspect before use and replace promptly if contaminated.
  • Apron: Use a chemical‑resistant apron whenever splash risks exist.
  • Handling aids: Use bottle carriers and secondary containment; keep containers low, capped and under control.

Decanting, dilution and mixing rules

Incidents often occur while decanting and diluting. Work in a fume hood. For acids, always add acid to water—specifically, add the more concentrated acid to the dilute—never water to acid. Pour slowly down the container wall rather than straight into the liquid.

  • Small increments: Neutralisation generates heat; add in small portions and pause.
  • Keep containers low: Work below eye level; use bottle carriers and containment.
  • Confirm compatibility: Check the SDS; some acid reactions release toxic or flammable vapours.

Spill response and first aid you should know

Protect people first, then contain. If a corrosive leaks, approach cautiously, don PPE and deploy your spill kit. For large spills, unknowns or strong vapours, evacuate and call your emergency number. Some acid reactions can release toxic or flammable gases; remove ignition sources.

  • Small spills (trained): Absorb, then neutralise (CaCO3 for acids; citric acid for bases), and containerise.
  • Eyes: Flush immediately for at least 15 minutes; hold lids open and roll eyes.
  • Skin: Remove contaminated clothing; wash for at least 15 minutes (use the emergency shower for large splashes).

Seek medical attention.

Special cases to treat with extra care: hydrofluoric acid and more

Some corrosive substances demand extra precautions. Hydrofluoric acid (HF) can cause delayed deep tissue injury and systemic toxicity; keep calcium gluconate gel on hand and follow HF‑specific emergency procedures. Others need chemical‑specific protocols due to volatility or oxidising power—always check the SDS before starting.

  • Hydrofluoric acid (HF): designated areas, calcium gluconate gel, immediate decontamination and medical review.
  • Concentrated hydrogen peroxide: corrosive and strong oxidiser; may react violently with organics.
  • Perchloric acid: consult SDS and local protocols; special procedures apply.

Transport compliance for class 8 under ADR, IMDG and IATA

For carriage, Class 8 is applied under ADR (road), IMDG Code (sea) and IATA/ICAO (air). Compliance starts with the UN number and proper shipping name, then any assigned packing group. The modal code you use will specify packaging, Class 8 marks/labels/placards, segregation from incompatibles and required transport documentation. Follow the code’s segregation rules to prevent heat or toxic/flammable vapours when acids contact incompatibles, and ensure stowage prevents leaks that could attack metals and structures.

Packaging, marking and documentation at a glance

For Class 8, use UN performance‑tested packaging compatible with the substance and its Packing Group. Mark with the Class 8 label plus UN number and Proper Shipping Name; add subsidiary risk labels if assigned. Provide mode‑specific dangerous goods documents showing UN number, Proper Shipping Name, class, packing group, quantity and emergency information.

Frequently confused hazards: skin corrosion vs corrosion to metals

Two distinct issues are often confused. Skin corrosion means a substance can destroy living tissue on contact (the basis for Class 8). Corrosion to metals is compatibility: the chemical attacks steel or aluminium, threatening packages, plant and vehicles; acids contacting metals can release flammable hydrogen. Controls differ: PPE/eyewash for skin risks; compatible packaging/containment for metal attack.

Practical checklist for working with corrosives

Use this quick check before any task with corrosive substances: read the SDS and label; set up a fume hood, eyewash and shower; wear splash goggles + face shield, compatible gloves and apron; segregate acids from bases; keep containers below eye level with bottle carriers; add acid to water; have spill kit and neutralisers (CaCO3/citric acid) ready.

Key takeaways

Corrosives (Class 8) destroy tissue and materials; pH, skin‑corrosion data and compatibility drive classification and controls. Separate acids and bases, store low with containment, wear splash PPE, use fume hoods, add acid to water, and prepare for spills and first aid. Need compliant procedures and training? Speak to Logicom Hub for ADR, IMDG, IATA support.