Interpretation Response #25-0137

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date: 09/24/2026

Company Name: Public Utilities Commission of Ohio

Individual Name: Rod "Chip" Moser

Location State: OH Country: US

View the Interpretation Document

Response text:

September 24, 2026

Rod "Chip" Moser
Chief, Transportation Compliance/Registration
Public Utilities Commission of Ohio
180 E Broad Street
Columbus, OH  43215

Reference No. 25-0137

Dear Mr. Moser:

This letter is in response to your October 8, 2025 email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) on cargo tanks and the performance requirements to prevent accumulation of material impairing the operation of the pressure relief systems. Specifically, you ask about the applicability of § 178.345-10(b)(6) as it relates to pressure relief device (PRD) components.

We have paraphrased and answered your questions as follows:

Q1. What part of the pressure relief device, e.g., the "rain cap," does § 178.345-10(b)(6) apply to?

A1. Section § 178.345-10(b)(6) refers to the entire pressure relief system, rather than an individual PRD or an individual PRD component. Under § 178.345-10(b)(1), a primary pressure relief system consists of one or more reclosing pressure relief valves (devices), and a "rain cap" or cover may be either a component of the PRD or a separate element of the broader system.

Q2. Does missing an "upper housing hole plug" as part of a PRD as shown in the example schematic provided constitute a violation of § 178-345-10(b)(6)?

A2. The requirement found in § 178.345-10(b)(6) is intended to ensure the pressure relief system is "mounted, shielded and drainable" to minimize the accumulation of material that could impair its operation. Noncompliance is determined on a case-by-case basis, considering not only the cargo tank design, but also the conditions and environment in which the cargo tank will be in use. If the absence of a single component, such as a the one you describe, affects the operation or discharge capability of the pressure relief system—by the accumulation of material that allows freezing, corrosion, or blockage—it may result in non-compliance.

Q3. Is it a violation if the "rain cap" is in place but the rubber plug is missing?

A3. See answer A2.

I hope this information is helpful. Please contact us if we can be of further assistance.

Sincerely,

Dirk Der Kinderen
Chief, Standards and Development Branch
Standards and Rulemaking Division

Regulation Sections