Why Material Compatibility Matters

The UK Environment Agency requires secondary containment (bunding) for bulk liquid storage under PPG2 and the Control of Pollution (Oil Storage) Regulations 2001. COSHH regulations demand that containment systems are suitable for the specific substances stored. But these legal frameworks only work if the containment material itself is chemically resistant to what it is designed to hold.

Consider these real failure scenarios:

• Zinc attack from alkalis: A galvanised steel drip tray was placed beneath a sodium hydroxide (caustic soda) drum. Within weeks, the NaOH had dissolved the zinc galvanising layer, creating zinc oxide sludge that contaminated the chemical and left bare mild steel exposed. The tray failed structurally within months, resulting in a full spill directly to floor drainage.
• PP dissolved by aromatics: A polypropylene IBC bund was used to contain toluene — a common aromatic solvent. The toluene caused the PP walls to swell and soften over several weeks, ultimately leading to a structural failure of the bund during a minor overfill event. Toluene entered the stormwater drain, resulting in an Environment Agency enforcement notice.
• EPDM seals and petroleum: A drum spill pallet fitted with EPDM drain valve seals was used for waste oil collection. The petroleum-based waste caused rapid swelling of the EPDM elastomer, jamming the drain valve open and allowing waste oil to bypass the containment system entirely.

These are not unusual cases. They represent common mismatches that occur when chemical compatibility is not systematically verified before purchasing containment equipment.

The consequences range from regulatory prosecution and Environment Agency enforcement notices to insurance voidance, serious environmental damage, and in the case of flammable or reactive chemicals, fire or explosion risk.

Material-by-Material Guide

Polypropylene (PP)

Polypropylene is the most widely used polymer in spill containment products — drum pallets, IBC bunds, portable bunds, and sump pallets are routinely manufactured in PP. It offers an excellent combination of chemical resistance, rigidity, UV stability, and cost-effectiveness.

PP is compatible with: Most inorganic acids (sulphuric acid up to 96%, hydrochloric acid, nitric acid at dilute concentrations), alkalis including sodium hydroxide and potassium hydroxide, alcohols (ethanol, methanol, isopropanol), hydrogen peroxide, sodium hypochlorite (bleach) at standard concentrations, and aqueous solutions generally.

PP is NOT suitable for: Aromatic hydrocarbons (toluene, xylene, benzene), chlorinated solvents (dichloromethane, trichloroethylene, chloroform), concentrated oxidising acids at elevated temperatures, and certain ketones at high concentrations. Aromatic solvents cause swelling and eventual dissolution of the polymer matrix — PP will not simply degrade slowly, it will lose structural integrity rapidly.

Typical PP containment products: Drum spill pallets, IBC spill pallets, portable bunding.

HDPE (High-Density Polyethylene)

HDPE offers slightly broader chemical resistance than PP, particularly for hydrocarbons and petroleum-based products. It is less rigid than PP but more impact-resistant at low temperatures. HDPE is commonly used for chemical storage tanks, IBC inner bottles, and specialist containment where petroleum products are stored alongside other chemicals.

HDPE is compatible with: Petroleum fuels (diesel, petrol), oils and lubricants, most inorganic acids (dilute concentrations), alkalis, alcohols, hydrogen peroxide, bleach, and most aqueous solutions. It offers somewhat better resistance to aromatic hydrocarbons than PP but is still not recommended for prolonged contact with concentrated aromatics.

HDPE is NOT suitable for: Concentrated aromatic solvents for extended periods, halogens, and some strong oxidising agents. Always verify with a chemical resistance chart for the specific grade and concentration.

Galvanised Steel

Galvanised steel bunds (hot-dip or electro-galvanised) are commonly used for petroleum and oil storage — particularly under fuel tanks, generators, and oil-fired boiler systems. The zinc coating provides cathodic protection against atmospheric corrosion and makes galvanised steel suitable for outdoor installations.

Galvanised steel is compatible with: Petroleum fuels (diesel, red diesel, kerosene, petrol), mineral oils, lubricants, and hydraulic fluids. It performs well in weathering environments when the zinc layer is intact.

Galvanised steel is NOT suitable for: Any acid (even weak organic acids), strong alkalis (caustic soda, potassium hydroxide), bleach, and aqueous salt solutions. Zinc is amphoteric — it dissolves in both acidic AND alkaline conditions. A pH below 6 or above 12 will cause rapid zinc dissolution. This is a critical failure mode that is frequently underestimated. For any chemical other than petroleum and oils, galvanised steel should not be used as a primary containment material without specialist corrosion engineering review.

Stainless Steel 316

Grade 316 stainless steel (18% chromium, 10% nickel, 2% molybdenum) is the specification for aggressive chemical environments and high-temperature applications. The molybdenum content provides superior resistance to pitting corrosion and chloride attack compared to grade 304. SS316 is used for pharmaceutical storage, food-grade applications, and chemical plant containment where contamination risk from polymer migration is unacceptable.

SS316 is compatible with: Most inorganic and organic acids at moderate concentrations, alkalis, solvents including alcohols and ketones, hydrogen peroxide, and many oxidising chemicals. It is the preferred specification for nitric acid bunding and for high-temperature service.

SS316 is NOT suitable for: Concentrated hydrochloric acid (chloride stress corrosion cracking risk), concentrated sodium hypochlorite, and environments with high chloride ion concentrations at elevated temperatures. For these specific chemicals, PP or specialist alloys should be specified.

SS316 represents a higher capital cost than polymer alternatives, but for aggressive chemicals, pharmaceutical applications, and situations requiring structural rigidity at elevated temperatures, it is the correct specification. Always consult a materials engineer for novel chemical combinations.

EPDM Seals (Ethylene Propylene Diene Monomer)

EPDM elastomer is used for drain valve seals, gaskets, and flexible connections in spill containment systems. Its chemical resistance profile makes it suitable for water, steam, dilute acids, alkalis, and polar solvents, but it has a critical incompatibility with petroleum products that must be understood by anyone specifying containment systems for fuel storage.

EPDM is compatible with: Water, steam, dilute acids and alkalis, ketones (acetone, MEK), alcohols, hydrogen peroxide, and sodium hypochlorite. It maintains flexibility and sealing performance across a broad temperature range in aqueous environments.

EPDM is NOT suitable for: Petroleum fuels, mineral oils, hydraulic oils, diesel, kerosene, or any hydrocarbon-based fluid. Oil causes EPDM to swell significantly — often to the point where seals jam in open or closed positions, or extrude from their housings. For petroleum containment, specify Nitrile (NBR) seals.

Nitrile / NBR Seals (Acrylonitrile Butadiene Rubber)

Nitrile rubber (NBR) is the standard seal material for petroleum products, fuels, and mineral oils. Its oil resistance is significantly superior to EPDM, making it the default specification for drum pallets and bunds used in fuel storage, oil distribution, and lubrication systems.

NBR is compatible with: Petroleum fuels, diesel, petrol, mineral oils, hydraulic fluids, greases, and engine coolant. It offers good resistance to moderate concentrations of dilute acids.

NBR is NOT suitable for: Ketones (acetone, methyl ethyl ketone), esters, chlorinated hydrocarbons, strong oxidising acids, and aromatic hydrocarbons at elevated concentrations. Contact with ketones causes NBR to swell severely and lose tensile strength rapidly.

Chemical Compatibility Table

The table below provides compatibility ratings for the 18 most commonly stored industrial chemicals against five containment materials. Ratings are based on standard chemical resistance data at ambient temperature (20°C) and typical industrial concentrations. Always verify ratings for specific concentrations, temperatures, and blend compositions with your containment supplier or a chemical engineer.

Key: ✅ Compatible — suitable for continuous contact | ⚠️ Limited — suitable for short-term/splash exposure, verify application | ❌ Not Recommended — avoid, risk of degradation or failure

Data provided for guidance at 20°C and typical industrial concentrations. Elevated temperatures, high concentrations, or chemical blends may alter compatibility ratings. Always consult a chemical engineer for critical applications.

How to Specify the Right Containment Material

When specifying spill containment for a new installation or reviewing an existing one, follow this systematic process:

1. Identify all chemicals stored in or near the containment area. Don't just consider the primary stored chemical — consider cleaning agents, transfer fluids, and anything that could realistically end up in the bund during a spill or overfill event.
2. Check concentration and temperature. A chemical that is compatible at 10% concentration and 20°C may be incompatible at 50% and 60°C. Always check the specific operational conditions, not just the chemical name.
3. Identify the most aggressive chemical in the mix. If you are storing both diesel and sulphuric acid in the same bunded area (e.g., a battery charging station adjacent to a fuel tank), specify a containment material that is compatible with the worst-case chemical — in this case, a polymer bund (PP or HDPE), not galvanised steel.
4. Check seal materials separately. The bund body material and the seal material may have different compatibility profiles. A PP bund body with EPDM drain seals is NOT suitable for petroleum — the seals will fail even if the body is chemically resistant.
5. Document your compatibility assessment. Under COSHH and Environment Agency guidance, you should be able to demonstrate that you have assessed material suitability. Keep records of your specification decisions.

Products by Application

• Drum storage — chemicals: PP drum spill pallets — suitable for acids, alkalis, alcohols, and aqueous solutions
• IBC storage — chemicals and fuels: IBC spill pallets — available in PP for chemicals or galvanised steel for petroleum
• Flexible/temporary bunding: Portable bunds — PVC or PE options available, suitable for a wide range of chemicals

Frequently Asked Questions

What is the best material for storing hydrochloric acid in a spill containment bund?

Polypropylene (PP) and HDPE are both excellent choices for hydrochloric acid containment. PP offers outstanding resistance to most inorganic acids including HCl at concentrations up to 35%. Stainless Steel 316 is also suitable but represents a higher cost option. Galvanised steel must be avoided as the zinc coating is rapidly attacked by acid.

Can I use a polypropylene spill pallet for diesel?

Yes, polypropylene is suitable for diesel and most petroleum-based fuels with short-term exposure. However, PP should NOT be used for aromatic hydrocarbons such as toluene, xylene, or benzene. For general petroleum products, both PP and HDPE pallets are widely used in compliance with UK Environment Agency bunding regulations.

Why is galvanised steel unsuitable for chemical bunding?

Galvanised steel has a zinc coating which undergoes rapid galvanic attack when exposed to acids or strong alkalis such as sodium hydroxide. This dissolves the zinc layer, exposing bare steel to corrosion. For chemical bunding, stainless steel 316 or polymer materials (PP/HDPE) are the correct choice.

What is the difference between EPDM and Nitrile seals?

EPDM seals are ideal for water, dilute acids, alkalis, and ketones, but are NOT compatible with petroleum oils or fuels. Nitrile (NBR) seals are excellent for petroleum products, fuels, and oils, but degrade rapidly in contact with ketones and esters. Always match the seal material to the chemical being contained.

Is Stainless Steel 316 always the safest option?

SS316 offers superior corrosion resistance to most acids, alkalis, and organic solvents. However, it is NOT suitable for concentrated hydrochloric acid (chloride stress corrosion cracking risk) or concentrated sodium hypochlorite. For these chemicals, PP or HDPE is often more appropriate. SS316 is also significantly more expensive than polymer alternatives.