PHMSA Harmonization NPRM – Corrosive Classification Process

Earlier this week I wrote about the recent publication of a notice of proposed rulemaking from DOT’s Pipeline and Hazardous Material Safety Administration (PHMSA) proposing the latest set of revisions to the hazardous material regulations (HMR) to harmonize those regulations with international hazmat shipping rules. Today I would like to address a specific portion of that NPRM; the classification process for corrosive materials in accordance with 49 CFR 173.137.

Overview

In section 4 of the NPRM, PHMSA briefly describes the changes to the HMR being proposed. With regards to the classification of corrosive materials it notes:

“Alternative criteria for classification of corrosive materials: PHMSA proposes to include non-testing alternatives for classifying corrosive mixtures that instead uses existing data on the chemical properties. Currently the HMR require offerors to classify Class 8 corrosive material and assign a packing group based on test data. The HMR authorize a skin corrosion test and various in vitro test methods that do not involve animal testing. However, data obtained from testing is currently the only data acceptable for classification and assigning a packing group. These alternatives would afford offerors the ability to make a classification and packing group assignment without the need to conduct physical tests.”

PHMSA is also proposing to update the incorporation by reference OECD Guidelines for the Testing of Chemicals to the 2015 version. Specifically, for the testing of corrosive materials for determination of packing group determination, this will affect OECD tests 404, 430, 431, and 435.

Along with the similar change to the definition of ‘corrosive material’ in 173.136, PHMSA is proposing to remove the phrase “full thickness destruction” and replace it with “irreversible damage” in all instances where it occurs in 173.137.

PHMSA is not proposing to add additional corrosivity testing protocols in this NPMR.

Corrosion Classification Alternatives

The proposed regulation provides two non-testing alternatives to determine the packing group containing mixtures of chemicals including one or more previously tested corrosive chemicals. The first, bridging {§173.137(d)(1)}, would be used when “there is sufficient data on both the individual ingredients and similar tested mixtures to adequately classify and assign a packing group for the mixture”. There are five bridging principals that could be applied to mixtures under this provision:

• Dilution;

• Batching;

• Concentration of mixtures;

• Interpolation within one packing group; and

• Substantially similar mixtures.

The second technique is the calculation method {§173.137(d)(2)}. This technique uses known concentration data and regulatory information from the Hazmat Table to calculate which packing group a product would be in. A proposed Appendix I helps translate the calculations into actual packing group determination.

Calculation Process

By their very nature, regulatory documents are not real clear in explaining how a process will work. After some careful reading of the NPRM and the proposed changes to §173.137 and the new Appendix I, this is how I see the calculation process working.

First, someone is going to have to make a technical determination of whether or not any interactions (or chemical reactions) will enhance the corrosive effects of any of the constituent materials. It that determination is positive, then physical testing will be required, or the organization will have to assume PG I status for the material.

Next all of the corrosive constituents of the product will have to be identified. The Hazmat Table (§172.101 table) will then be used to determine the packing group and any minimum concentration limit associated with that material in the Table. That minimum concentration limit is called the ‘specific concentration limit (SCL)’ in this NPRM. Unfortunately, it is not specifically defined.

The first calculation will only involve PG I corrosive constituents of the product. For each PG I corrosive constituent the ratio of its concentration in the product to the SCL will be determined. For most corrosive materials, the Hazmat Table does not provide an SCL; for those chemicals a generic concentration limit (GCL; again, not specifically defined in the NPRM) of 1% will be assumed for this initial calculation. The sum of all of the PG1/SCL(GCL) ratios will be determined. If that sum is greater than or equal to one, Calculation #2 will be completed. If the sum is less than 1%, Calculation #3 will be completed.

Calculation #2. Again, just the concentration and GCL for the PG 1 corrosive materials in the product will be used. In this case (and in all subsequent calculations) the GCL will be equal to 5% and the concentration ratios for all PG I will be recalculated. If the sum of those ratios is greater than or equal to 5% then the material will be classified as Class 8, PG I. If the sum of those ratios is less than 5%, the material will be classified as Class 8, PG II.

Calculation #3. This calculation will use the same data from all PG I and PG II chemicals in the material being classified. Where a SCL is provided it will be used in the ratio calculation described above. Otherwise, a GCL of 5% will be used. The ratios for each of the PG I and PG II chemicals will be summed. If the sum is greater than or equal to 5%, the material will be classified as Class 8, PG II. If the sum is less than 5%, Calculation #4 will be completed.

Calculation #4. This calculation will use the same data from all PG I, PG II and PG III chemicals in the material being classified. Where a SCL is provided it will be used in the ratio calculation described above. Otherwise, a GCL of 5% will be used. The ratios for each of the PG I, PG II and PG III chemicals will be summed. If the sum is greater than or equal to 5%, the material will be classified as Class 8, PG III. If the sum is less than 5%, the material will not be classified in Class 8.