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Section §173.124: Class 4, Divisions 4.1, 4.2 and 4.3-Definitions

Below are the available interpretations and guidance for the given section. To return to the list of parts, use the Parts link above. If you do not see any guidance or interpretation information below, that means there is none available for the given part/section. Return to the search page to browse additional regulations sections.

PHMSA has published several Frequently Asked Questions (FAQ) documents on regulatory topics. Please review our FAQ documents below:

Additionally PHMSA has Hazardous Materials FAQs based on letters of interpretation on the following topics:

This section of the website provides the ability to find regulations information including regulations parts, content of sections, and interpretations for regulations sections. Below is a list of parts, identified by the part number and subject. To browse sections by part, click on the subject link below. You will be taken to the eCFR website to view sections for a part.

A written regulatory interpretation, response to a question, or an opinion concerning a pipeline safety issue may be obtained by submitting a written request to the Office of Pipeline Safety (PHP–30), PHMSA, U.S. Department of Transportation, 1200 New Jersey Avenue SE., Washington, DC 20590–0001 or at the email address: In addition to email address, the requestor must include his or her return address and should also include a daytime telephone number. Requests should be submitted at least 120 days before the time the requestor needs a response.

Note: electronic submission is provided as alternative to the 49 CFR Part 190.11(b) mail-in requirement.

The regulations text of the section can be found on the eCFR website. To view the regulations text, use the link below. For assistance, please send an email to

View section 173.124 on the ECFR website

Interpretation Responses

Ref ID Date Company Name Individual Name Response Document
23-0105 SET Environmental, Inc. David Olsen, Jr. View
20-0084 LANXESS Corporation Cyndi Fink View
18-0087 Scarpa Consultants Nicholas Scarpa, Ph.D. View
98-0345 Neal Langerman, Ph.D. View
09-0262R Elkem Metals, Inc. Mr. George Scott View
01-0179 W. R. Grace Co.-Conn Mr. Michael P. DeCiceo View
13-0161 Royal Oak Enterprises LLC Mr. Phillip Zimmerman View
16-0189 CTI and Associates, Inc. Ms. Terri Zick View
09-0273 Dow Corning Corporation Mr. Stephen V. Moser View
03-0131 Design & Product Development IDEO Chicago Mr. Iain Roberts View
08-0277 Mr. Lawrence W. Bierlein View
01-0178 W. R. Grace Co.-Conn Mr. Michael P. DeCicco View
09-0300 Sartorius Stedim Filters, Inc. Mr. José H. Braulio-Martinez View
98-0524 Hunt Shipmate, Inc. Mr. Steven Charles View
08-0046 Mr. Stanley Peterburgsky View
98-0525 Elkem Metals Company Ms. Sharon L. Thompson View
03-0254 CONSIDAR, Inc. Ms. Noreen McDonald View
98-0133 Sumitomo Corporation of America Mr. Thomas M. Riederer View
13-0114 WTS, Inc. Mr. James Moulds View
02-0183 Exotherm Technology, Inc. Robert W.Stephens View
12-0127 Veolia ES Technical Solutions, L.L.C. Ms. Jennifer Eberle View
11-0122 Safety Management Services Inc. Mr. A. Garn Butcher View
13-0031 Minigrip Mr. Ben Hellming View
04-0110 Bécancour Silicon Inc. René Boisvert View
08-0025 HMT Associates, L.L.C. Mr. E.A. Altemos View
02-0291 Exotherm Technology, Inc. Robert W. Stephens View
08-0214 DuPont Global Logistics Mr. Kevin Greene View
09-0044 Restek Corporation Mr. Erik Perrin View
08-0293 S.H. Bell Company Mr. Chris McKenzie View
09-0058 Thermo Fisher Scientific, Customer Channels Group Mr. Gene Sanders View
03-0218 CONSIDAR, Inc. Ms. Noreen McDonald View
08-0154 Symmetricom Mr. Gerald M. Beauchesne View