A corrosive classification can have significant implications for a product. It can affect hazard labelling, Safety Data Sheet (SDS) information, shipping requirements, packaging, handling procedures, and associated costs.
In some cases, a product may initially be classified as corrosive based on its ingredients, formulation data, or a conservative classification approach. Laboratory testing provides an opportunity to evaluate the finished product itself and determine whether that classification is supported by test data.
Corrosion testing may be useful when a company wants to:
- Investigate whether a corrosive classification can be downgraded or removed
- Reduce shipping, packaging, or labelling requirements where supported by test results
- Meet Transportation of Dangerous Goods (TDG) proof of classification requirements
- Generate product-specific data rather than relying solely on ingredient-based calculations
- Better understand the hazards of a new or reformulated product
- Support SDS preparation or classification
- Confirm whether a formulation change has affected the product’s corrosive properties
The appropriate testing strategy depends on the classification being investigated and the regulatory purpose of the data.
Corrosive to Skin vs. Corrosive to Metals
“Corrosive” does not describe a single test endpoint.
For hazard communication purposes, corrosion to skin and corrosion to metals are separate hazard classes. For transport, either skin corrosion or corrosion to metals may be relevant to determining whether a product meets Class 8 criteria.
This means that a product that is not corrosive to skin is not automatically non-corrosive for transport. Corrosion to metals may still need to be evaluated.
The amount of sample required for these tests is also very different. OECD 435 skin corrosion testing requires approximately 25 mL of sample, while UN TDG corrosion-to-metals testing requires approximately 3 L.
For this reason, the order of testing can make a considerable difference for a client.
Starting With Skin Corrosion Testing
Dell Tech Laboratories typically recommends starting with OECD 435 skin corrosion testing when investigating a corrosive transport classification.
OECD 435 is an in vitro membrane barrier test used to identify substances and mixtures that are corrosive to skin. Only approximately 25 mL of sample is required.
If the product is found to be corrosive to skin, it can meet the criteria for a Class 8 corrosive classification for transport. In that case, there may be little benefit in immediately proceeding with a test that requires several litres of additional product if the client’s objective is to determine whether the Class 8 classification can be removed.
Starting with OECD 435 can provide an answer to the first classification question using a relatively small quantity of sample.
What If the Product Is Not Corrosive to Skin?
A non-corrosive result from OECD 435 is good information, but it does not necessarily resolve the transport classification.
The next step may be UN TDG corrosion-to-metals testing.
This method evaluates the corrosion rate of the product against steel and aluminum. A corrosion rate exceeding the applicable threshold of 6.25 mm per year at a test temperature of 55°C can result in a Class 8 transport classification.
The practical difference is sample volume. Corrosion-to-metals testing requires approximately 3 L of product.
A staged approach can therefore look like this:
- Submit approximately 25 mL for OECD 435 skin corrosion testing.
- If the product is corrosive to skin, the corrosive transport classification is supported and further testing may not be necessary for that particular objective.
- If the product is not corrosive to skin, submit the larger sample volume for corrosion-to-metals testing.
- If the product does not meet the applicable criteria for either endpoint, the combined test data may provide the evidence needed to support removal of the corrosive transport classification.
This sequence can be particularly useful when shipping large quantities of the product to the laboratory is difficult or expensive. It may also avoid the need to ship and dispose of 3 L of a product that has already been demonstrated to meet Class 8 criteria through skin corrosion testing.
Supporting TDG Proof of Classification
Corrosion testing can also be useful for companies looking to establish or maintain documentation supporting their transport classification.
Under TDG requirements, consignors are responsible for determining the classification of dangerous goods before transport and maintaining the applicable proof of classification. Laboratory test results can provide product-specific evidence to support the classification decision.
This can be particularly valuable when existing formulation information leads to a conservative Class 8 classification, but the company has reason to believe that the finished product may not meet the applicable corrosivity criteria.
Rather than relying on an assumption that the product is less hazardous, testing provides objective data that can be retained as part of the technical basis for the classification.
Potential Benefits of Removing an Unnecessary Corrosive Classification
Where supported by the test results and applicable regulations, removing or downgrading a corrosive classification can have practical benefits.
Depending on the product and regulatory framework, these may include reduced dangerous goods shipping requirements, different packaging requirements, simplified hazard communication, and lower transportation or handling costs.
There is also value beyond cost savings. Accurate classification gives manufacturers, distributors, workers, carriers, and customers a better understanding of the actual hazards associated with the finished product.
The goal of testing is not simply to obtain a “non-corrosive” result. It is to generate data that supports an accurate and defensible classification.
What About Canadian Consumer Products?
Products subject to Canada’s Consumer Chemicals and Containers Regulations, 2001 (CCCR, 2001) have additional considerations for corrosive classification. Depending on the product and its pH, acid or alkali reserve testing may be used as part of the classification process.
This testing evaluates how much acid or base a product holds in reserve and can help distinguish between products that are corrosive, irritant, or non-hazardous under CCCR, 2001.
For a closer look at how pH and acid/alkali reserve work together for Canadian consumer product classification, read our article, Beyond pH: Acid Alkali Reserve Testing Determines Corrosive Hazards Under CCCR, 2001.
What About Skin and Eye Irritation?
A product does not have to be corrosive to cause irritation.
If testing determines that a product is not corrosive, additional testing may be appropriate to evaluate less severe effects. Dell Tech Laboratories also offers dermal irritation and ocular irritation testing to help characterize potential skin and eye hazards.
Eye corrosion and irritation are relevant to hazard communication and SDS classification, but are not used to determine whether a product meets Class 8 criteria for transport.
The appropriate combination of corrosion and irritation testing will depend on the product, its existing classification, and the regulatory question being investigated.
Choosing a Testing Strategy
There is no single corrosion testing plan that is appropriate for every product.
If the objective is to investigate a Class 8 transport classification, starting with the smaller-volume OECD 435 test can be an efficient approach. If the product is not corrosive to skin, corrosion-to-metals testing can then be performed to investigate the remaining basis for the transport classification.
If the objective is broader SDS hazard characterization, both skin corrosion and corrosion-to-metals endpoints may need to be considered because they represent separate hazard classes.
Understanding the reason for testing before selecting the method helps ensure that the laboratory data answers the right classification question.
Need help determining which corrosion test is appropriate for your product? Dell Tech Laboratories can help identify a testing approach based on your current classification, product type, sample availability, and intended use of the results.
Blog Author
Kate Hatherley
Katherine supports analytical testing in Dell Tech’s Lab Services. Prior to joining Dell Tech’s Lab Services Group in 2019, Katherine worked in project administration and geographic information systems in the Ontario forestry industry.
