# Truck Trailer Manufacturing Association — Hazardous Materials Safety Interpretation - **operation:** document - **citation:** 17-0065 - **title:** Truck Trailer Manufacturing Association — Hazardous Materials Safety Interpretation - **source type:** guidance - **agency:** Pipeline and Hazardous Materials Safety Administration - **status:** guidance - **official:** true - **published on:** 2018-07-23 - **effective on:** Not available - **summary:** 17-0065 response to Truck Trailer Manufacturing Association concerning 178.345, 178.347, 180.407. - **machine formats:** - **json:** https://regulus.evalyn.ai/document/phmsa-interpretation-17-0065.json - **markdown:** https://regulus.evalyn.ai/document/phmsa-interpretation-17-0065.md - **app url:** https://regulus.evalyn.ai/document/phmsa-interpretation-17-0065 - **source url:** https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/standards-rulemaking/hazmat/interpretations/58541/170065.pdf **body:** <<>> U.S. Department of Transportation 1200 New Jersey Avenue, SE Washington, DC 20590 Pipeline and Hazardous Materials Safety JUN 15 2018 Administration Mr. John Freiler Engineering Manager Truck Trailer Manufacturing Association 7001 Heritage Village Plaza, Suite 220 Gainesville, VA 20155 Reference No. 17-0065 Dear Mr. Freiler: This letter is in response to your July 6, 2017, letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the installation of U.S. Department of Transportation (DOT) 400-series cargo tank vents on Motor Carrier (MC) 300-series cargo tank motor vehicles (CIMV). Specifically, you include in your letter two scenarios and enclose guidance documents and a technical bulletin from your organization; one driver/vehicle examination report; and a clarification letter on this topic issued by the Research and Special Programs Administration, the predecessor agency of the Pipeline and Hazardous Materials Safety Administration (PHMSA). We have paraphrased and answered your questions as follows: Scenario 1: An MC 307 CTMV fitted with a 30-pounds per square inch gauge (psig) pressure relief device (PRD) has a set discharge pressure of 30 psig (or maximum allowable working pressure (MAWP)) to 33 psig (110% of MAWP); see superseded $§ 178.342-4(c) and 180.407()(1)(ii)(A). However, per the requirements in § 180.4070)(1)(ii)(B), a vent upgraded to conform to DOT 407 specifications on a 30 psig MAWP CTMV would be required to open between 36 psig (120% of MAWP) to 39.6 psig (132% of MAWP); see §§ 178.347-4(c) and 178.345-10(d)(1). 01. Based on Scenario 1, when upgrading an MC 307 CTMV PRD to a DOT 407 CTMV PRD, is the correct set-to-open pressure 120-132% of MAWP? A1. An MC 307 PRD modified to conform to DOT 407 specifications on a 30 psig MAWP CTMV would be required to open between 36 psig (120% of MAWP) and 39.6 psig (132% of MAWP), as prescribed in §§ 180.407()(1)(ii)(B), 178-347-4(c), and 178.345- 10(d)(1). <<>> Scenario 2: An MC 307 CTMV with a 30 psig MAWP originally had a PRD flow rated at 130% or 39 psig. The original MC 307 design specification limited the flow to 130% per superseded § 178.342- 4(0). In this case, the upgraded PRD would flow at 150% per the test pressure requirements prescribed in § 178.347-5; it would negate the requirement in paragraph (b) of superseded § 178.342-4 and conform to the PRD requirements stated in § 178.345-10. Q2. Based on Scenario 2, when upgrading an MC 307 CTMV PRD to a DOT 407 CTMV PRD, is the correct flow pressure equal to the CTMV's test pressure? A2. As prescribed in § 178.345-10(e), a DOT 400-series CTMV's flow rating is determined at a pressure not exceeding the CTMV's test pressure. Per § 178.347-5(b), the test pressure of a DOT 407 CTMV must be the greater of 40 psig or 1.5 times (150%) its MAWP. Thus, the flow pressure for Scenario 2 must be no more than 45 psig, provided the minimum venting capacity is met. I hope this information is helpful. Please contact us if we can be of further assistance. Sincerely, I. Alexs Taste T. Glenn Foster Chief, Regulatory Review and Reinvention Branch Standards and Rulemaking Division <<>> stevens $180.405 (c)(2)(Ur) aro o lank TTMA 7006. TRUCK TRAILER Assulacturers lank Conterence TTMAnet.org Since 1941 7001 Heritage Village Plaza • Suite 220 • Gainesville, VA 20155 • 703-549-3010 Jeffrey M. Sims • President July 6, 2017 U.S.DOT PHMSA-Office of Hazardous Materials Standards Attn: PHH-10 East Building Washington, DC 20590 1200 New Jersey Ave, SE Phmsa.hm-infocenter@dot.gov Subject: Request for Interpretation - Venting Upgrades Dear Sirs, We are requesting formal interpretation of the provisions to upgrade venting as provided for under sections 180.405(c)(2)(iv) and 173.33(d)(3) of title 49 CFR especially in light of a recent citation issued to Harnett Trucking (copy attached). In that case, a specification MC-307 cargo tank with upgraded vents meeting the DOT 407 requirements was cited for not meeting 178.343-4 and 180.405(c). The violation claims that the tank failed the inspection due to the inclusion of a DOT 407 vent on an MC-307 cargo tank. This specific tank was manufactured with MC-307 specification required reclosing and fusible vents, and was upgraded post construction. However, many tanks built during the early '90s were constructed as MC-307 or 312 cargo tanks with vents upgraded to DOT 407 or 412 vents similar to this tank as provided for in the HMR: 180.405(c)(2) A cargo tank of a specification listed in paragraph (c)(1) of this section may have its pressure relief devices and outlets modified as follows: (iv) A Specification MC 307 cargo tank, to conform with a Specification DOT 407 cargo tank (See $$178.347-4 and 178.345-11 of this subchapter). And 173.33(d)(3) A cargo tank motor vehicle made to a specification listed in column 1 may have pressure relief devices or outlets may be modified to meet the applicable requirement for the specification listed in column 2 without changing outlets conforming to the applicable specification to which the tank was constructed, or the pressure relief devices or the markings on the tank specification plate. The venting capacity requirements of the original DOT cargo tank specification must be met whenever a pressure relief valve is modified. Column 1 Column 2 MC 307 DOT 407. <<>> It has been standard industry practice to apply upgraded venting when the opportunity presents, as the new venting was seen to be safer as it banned non-reclosing devices such as fusible caps or rupture discs except when under a reclosing pressure relief device, and provided for greater product retention in an overturn due to the higher set pressures. When the caution in 173.33(d)(3), "The venting capacity requirements of the original DOT cargo tank specification must be met whenever a pressure relief valve is modified" is brought up, stakeholders relied on the 1996 letter of interpretation signed by Hattie Mitchell stating that the caution is not intended to prevent upgrades that are flow rated according to the DOT 400 specification, i.e., vents that achieve their flow rate only at the tank test pressure rather than the 130% of MAWP. The caution is there to require that flow rates be checked carefully against the requirements anytime the pressure relief devices are modified. That letter referenced 180.405(h)(3) which says: As provided in paragraph (c)(2) of this section, the owner of a cargo tank may elect to modify reclosing pressure relief §178.345-10 of this subchapter must provide the minimum venting capacity required by the original specification to devices to more recent cargo tank specifications. However, replacement devices constructed to the requirements of which the cargo tank was designed and constructed. Given the similarity in language between the caveat here and the language in 173.33(d)(3) stakeholders have understood that the flow rates of vents that have been upgraded is to be determined as required for the new specification: i.e. at tank test pressure per 178.345-10.- Additionally, PHMSA recently added 180.407(), Pressure Vent Bench Test, to make the opening pressures for vents clearer. For an MC-307 tank with vents upgraded to DOT 407 the code requires that the vents be set "according to the pressures set forth for a DOT 407 cargo tank in $178.347-4 of this subchapter." See 180.4070)(1)(ii)(B). §178.347-4 requires that pressure vents be set in accordance with §178.345-10(d), which states: (d) Settings of pressure relief system. The set pressure of the pressure relief system is the pressure at which it starts to open, allowing discharge. (1) Primary pressure relief system. The set pressure of each primary relief valve must be no less than 120 percent of the and remain closed at lower pressures. MAWP, and no more than 132 percent of the MAWP. The valve must reclose at not less than 108 percent of the MAWP It's clear that when a MC-307 cargo tank has its pressure relief devices upgraded, the HMR requires that they will conform in all ways to the upgraded specification. That is, it is set and flow rated according to the DOT 407 specifications at the cargo tanks test pressure and the original specification is consulted only to determine the required flow rate for the cargo tanks surface area at to be in compliance. " We believe that this citation, if allowed to stand, will create a safety risk for these tanks with upgraded venting. The upgraded vents are better performing and the prohibition against non- reclosing vents and higher set pressures means that retention of the hazardous commodity being transported is maximized. The consequences of allowing this citation to stand is to essentially outlaw upgrades: carriers will change back to MC-307 vents and fusible caps and lose the safety gains with the newer DOT 407 venting. Additionally, MC-307 cargo tanks with vent upgraded to DOT 407 specifications venting has been the industry norm for about 25 years without a reported incident caused by the use of these upgraded vents; a change now would be a tremendous waste of resources, causing confusion and the possibility of worker injury or mistaken vents being placed during the unnecessary and unwarranted change. <<>> Background on the addition of the provision in 173.33(d)(3) requiring "The venting capacity requirements of the original DOT cargo tank specification must be met whenever a pressure relief valve is modified": those meetings, there was much concern expressed by vent makers in regard to the so-called "Smart Vent" or "Dual This provision was added to the code in response to comments made at public meetings that I attended. At Function" requirements ‹ the reduced leakage during surge requirements laid out in (b)(3) (b)(3)}. Betts Industries, a leading Manufacturer of vents for MC-306 cargo tanks had developed a style of vent for the DOT 406 requirements that would leak less than one gallon during surge (the proposed requirement at that time), but those vents had a reduced capacity at the set and flow rate pressures for a DOT 406 cargo tank when compared to the vents currently in service on MC-306 tanks. It was felt that a potential safety hazard existed wherein a MC-306 cargo tank operator could replace his existing vents one for one with the new smart vents, not realizing that their capacity as measured at the DOT 406 pressures would be lower in terms of SCH than that cargo tank originally required. This lead to the following entry in the Federal Register Vol. 59, No. 212, Thursday, November 3, 1994, pg. 55163 & 55169: Page: 55163: Section 173.33 Consistent with the changes made in § 180.405(h) in this final rule, a new sentence is added to paragraph (d) stating that the venting requirements of the original DOT cargo tank specification must be met whenever a pressure relief valve is modified to a more recent specification. See preamble discussion for § 180.405(h). Page: 55169: Section 180.405 valve must be capable of re-seating to a leak-tight condition after a pressure surge. Section 180.405(c) Paragraph (h) specifies that replacement for any pressure replacement for any reclosing pressure relief authorizes modifying the reclosing pressure relief valves of an MC 306 cargo tank by installing the dual function pressure relief valves which are required for DOT406 cargo tank motor vehicles. Commentators pointed out that this replacement could result in an MC 306 cargo tank having lower emergency venting capacity than its specification requires: because it is difficult to produce a valve that achieves the comparatively high flow rates of the MC 306 units, withstands the pressure surges specified in the DOT 406 specification, and recloses with minimal loss of lading. A reduced flow capacity is less likely to be encountered in fitting and MC 307 with a DOT 407 valve replacement, and in fitting an MC 312 with a DOT 412 valve replacement, because of the larger pressure differentials which are commonly used in these cargo specification must be met whenever a pressure relief valve is replaced. .. tanks. Regardless of the equipment installed, the venting requirements specified in the particular cargo tank <<>> Q1. When upgrading an MC-307 cargo tank's pressure relief device to a DOT 407 pressure relief device, is the correct set to open pressure 120% to 132% of MAWP? For example, an MC-307 30psig pressure relief device has an allowable set to discharge pressure of 30psig (or MAWP) to 33psig (110% of MAWP); see §178.342-4 (c) and §180.407()(1)(ii)(A). However, per the requirements in 8180.4070(1)(i1)(B), a vent upgraded to conform with DOT 407 specs on a 30psi MA WP cargo tank would be required to open between 36psig (120% of MAWP) to 39.6psig (132% of MAWP); see §§178.347-4(c) & 178.345- 10(d)(1). Q2. When upgrading an MC-307 cargo tank's pressure relief device to a DOT 407 pressure relief device, is the correct FLOW PRESSURE equal to the tank's test pressure? For example, an MC-307 tank with a 30psig MAWP normally has a pressure relief device flow rated at 130% or 39psig. The original design regulation specification limited the flow to 130% per §178.342-4 (b). So, in this case, the upgraded pressure relief vent would flow at 150% per the test pressure requirements stated in §178.347-5. It would negate the requirement in section (b) of §178.342-4 and conform to pressure relief requirements stated in §178.345-10. We understand that PHMSA and the industry share the position that safety is enhanced with upgraded vents. We hope we can continue this cohesiveness and further hope that an expeditious clarification will prevent needless wasted efforts and the degradation to safety and risks to workers with needless vent replacements. If you have any questions at all, please feel free to contact me. Sincerely, John Freiler John Freiler Engineering Manager cc Glenn Foster, Chief, Regulatory Review and Reinvention Stan Staniszewski Encl. Background on 173.33(d)(3) 1996 Hattie Mitchell Letter Harnett Trucking citation and supporting photos. TTMA Position paper on Venting Upgrades TB 126 Bench Testing Pressure Relief Devices <<>> interp INTERPRETATION U.S. Department of Transportation Washington, D.C. 20590 400 Seventh Streel. S.W. Special Programs Research and Administration Ref. No. 96-1094 JUN I O 1996 Mr. John Freiler Senior Pröject Engineer Girard Equipment, Inc. PO Box 302-B Rahway, NJ 07065 Dear Mr. Freiler: This is in response to your letter requesting clarification of the pressure relief requirements specified in 49 CFR 173.33 (d) . Specifically, you asked if $ '173.33 (d) (3) prohibits upgrading vents on MC 307 and MC 312 cargo tanks to DOT 407 and DOT 412 vents that are flow rated in accordance with § 178.345-10. I apologize for the delay in responding and regret any inconvenience it may have caused. The answer is no. Section 173.33 (d) (3) provides that pressure vehicle listed in column 1 may be modified to meet the applicable relief devices. or outlets on a specification cargo tank motor requirements for the specification listed in column 2. However, replacement devices constructed to the requirements of § 178.345- original specification to which the cargo tank was designed and 10 must provide the minimum venting capacity required by the constructed. See § 180: 405 (h) (3). I trust this satisfies your inquiry. sincerely, Hothe z. michell Hattie I. Mitchell, Chief Office of Hazardous Materials Standards Exemptions and Regulations Termination 173.33(0) 961094 <<>> Jun 071702:48p p. 1 DRIVER/VEHICLE EXAMINATION REPORT Aspen 3.0.0.17 Illinois Division Federal Motor Carrier Safety Administration Report Number: US1459000551 3250 Executive Park Drive Inspection Date: 05/16/2017 Springfield, IL 62703 Start: 02:24 PM CT End: 3:26:14 PM CT Fax 217-492-4986 Inspection Level: |- Full HM Inspection Type: Bulk L T HARNETT TRUCKING INC 7431 STATE ROUTE 7 Driver: STILTNER, JIMMY R KINSMAN, OH 44428 License#: RU636599 State: OH MC/MX#: 170992 USDOT#: 00239562 Phone#: (330)876-2701 Date of Birth: 03/27/1944 State#: Fax#: CoDriver: License#: Location: MARSHALL SCALES Date of Birth: State: County: CLARK, IL Highway: 170 WB MilePost: 151 rigin: COLUMBUS, OF Shipper: OPC POLYMERS Destination IMPERIAL, MC Bill of Lading: 66877 Cargo: LIQUIDS/GASES IN TANKS VEHICLE IDENTIFICATION 1 Unit Type Make Year State 1 TT INTL 2006 OH Plate # Equipment ID VIN 2 ST POLA 1994 OH TPL9175 PVR7200 4 GWR CVSA# CVSA Issued # OOS Sticker 2865 2HSCNAPR66C301602 52,000 1PMS34227R1012865 58,000 BRAKE ADJUSTMENTS Axie # 11/8 1 2 Chamber Left Right L-20* 1 1 1/8 3 3/8 3/4 4 L-30 L-30 3/4 11/4 5/8 1 C-30 C-30 1 1/4 VIOLATIONS 393.45PC Vio Code 393.45 Section Unit OoS Citation # Verify Crash Violations Discovered Brake Tubing and Hose Adequacy - Connections to Power 393.45B2PC 393.45(b)(2) 2 N N N Brake Hose or Tubing Chafing and/or Kinking - Connection to Unit: Axle 2 Left Emergency hose cut core exposed 178.342-4 180.405(c) 2 N N N MC307 venting: MC307 (30psig MAWP) equipped with MC407 Power Unit: Servie side chafing rubbing against cat walk • vent with a set pressure of 36psig (MAWP). HazMat: 3 Flammable Special Checks: No Data for Special Checks. Placard: Yes Cargo Tank: 407 Pursuant to authority contained in Title 49, Code of Federal Regulations, Section 396.9(c), I hereby declare vehides with detects followed by an "Y' in the "Out of Service" column in the service defects have been repaired and the vehicles have been restored to safe operating condition. violations discovered section of this repart OUT OF SERVICE. No person shall remove the out of service stickers applied to these vehicles, or operate such vehicles until the out of Signature Of Repairer X: Facility ELS Date S16-/8 поитонских Fon Sult Date: 66-7-17 Page 1 of 1 Stitue 00239562 IL US1459000551 <<>> Harnett Trucking • DOT407 violation of MC307 upgrade 3 <<>> VEG EV: POLAR TANK TRAILER INC. MONTH AND YEAR IN WHICH FINAL GROSS VEHICLE WEIGHT RATING STAGE MEG. IS COMPLETED: LBS GROSS AXLE WEIGHT PATING AXLE NO. GROSS WEIGHT RATING ALL (FROM FRE OF VEHICLE CLAS WITH ERIMS, AT. TIRES (FROM FRE OF VEHICLE FRIE FROM 2R BENEMIES TIRE GERMS. AL THIRDERO ECONOMS TALLAN LERAL NOTOR VEHICLE SAFETY SIANDAS EATBOF MANUFACTURE SINOWN JEHICLE DOEN THIGATON NO ILLE ASSIFICATION OF VI HIGLA <<>> MANUFACTURED BY POLAR TANK TRAILR MFG. SERIAL R1-12865 MFG. LATE 77 68 D.O.T. SPEC. MC COT ORIGINAL TEST 7795 CERTIFICATION DATE 7/2 DESIGN PRESSURE 30 S.J.G. TEST PRESSURE SIG HEAD MATL 212MINTEG SHELL MAT'L WELD MAT'L 8116 LINING MAPL NOMINAL COMP'T CAP (FRONT TO REAR) U.S. SALS MAX. PROD. W 58000 LBS GAL MAX. PROD LOA LBS. MAX. TEMP LOADING EMI CHEN UNLOALING LIT O MONE SP2865 F-NNIN <<>> From:614 630 8886 05/16/2017 17:08 #926 P.006/011 #2865 Cl TREMCAR TREMCAR U.S.A. INC. 135 12t1 Street NE. • Strasburg. Ono 14bbo TANK TRAILER SPICIALISTS Prune: 330-8/8-1708 • Fax 320-878-5074 • Iol Free: 088-TREMCAR EXTERNAL VISUAL INSPECTON REPORT DOT NUMBER: CT-10556 in accordance with 49 CFR pat 180 Para. 180.470 (d)) R Stamp Repalr Required ฿ R -6563 Yes_ No Customer L..T. MARNETT MC/DOT No..... 307 Manufacture._ Date... 3-14 binE SerialNo. 1PMS 34221R101286 Unit No._..... 2865 Year of MFR. 1993 Original shell thickness.... NA Original head thickness MAWP/Design Pressure. _30 Min. Shell Thickness →121 Min. Head Thickness .112 N/A Cargo Tank Is Jacketed Cap. Comp. 1. 7000 insulated N/A Ryes \ Yes No Special Service Last Service Date. _No _NO Last Service Product 2-16 -... Last Service Miles .. "Cargo tank used to haul product corrosive to tank (Required every two years for tank in corrosive service) Upper Coupler Assembly Remored -X. res X res ...No _No INSPECTION STEPS Acceptable Non- See Acceptable Corrective 1.Shell and heads: condition of wells-dents- Action 2.Upper coupler assembly; condition of plate- Gouges-corrosion or abrasion…........ Valve installations-valve operator installation- 3.Bolted attachments: piping brackets and supports Undercarriage attachments Dust cap retainers-all tank-to-frame and/or 4. All major appurtenances and structural attachments On the cargo tank, including suspension system Members, outriggers and boister.............. Attachments, connecting structures, framels, cross" t 5. Piping and all valves and adapters: attachments- Leakage-handles and levers-cables or alr lines- Shear sections duit caps all gaskets or ortings: X lubrication poin........ (Normal, remote, and thermal)- function check- 6. Internal valve operation: three means or closure <<>> From:614 539 8886 06/16/2017 17:10 #925 P.010/011 *: - TREMCAR TREMCAR U.S.A. INC. 136 121h Streel Ni - Straspurg, Ohio i 1680 TANK THALEP SPErIALISTS Phone 330-878-7708 • fax: 330-878 3074 • Toll Freo' 886 TREMCAR DOT NUMBER: CT-10556 _Hydrostatic or pneumatic, EPA Mettrod 27- when applied LEAK TEST REPORT Test Liquid MR oveR Mee in accordance with 49 CFR Part 180 Para. 180.407 [h) Stamp Required... Yes _No MC/00 ....... Customer LT. MARNETT #R-6563 307 Date. 3-14-17 serial No. J PMS 34227R1012865 Unit No.. 2865 Year of MFR. Manufacture.... POLAR 1993 Original shell thickness MAWP/Design Pressure 30 Material Min. shel Thickness 316 121 Min. Head Thickness Original head thickness. 112 NA Insulated _Yes._ No Comp 1 араст Test pressure 24.0 Start Time End Time Comp. 3 Comp. 7 7:56 7:41 Comp. 4 Comp. 5. Vents Removed & Tested Set To Discharge Comp. 1 N 2 Open Pressure 368 4 5 Vent Type Reseal Pressure 36,0 33,0 Disposition GIRARD 30 * 407 Remarks Removed Replaced Reinstalled after completing bench test requirements Including normal yents if ok. The following must be completed for each compartment. Red fisg all vents removed or rendered Inoperative. Reinstall vents Acceptable (See Remarks) Nonacceptable Install test fitting into manhole assembly Manhole, open internal valve (if appropriate) Cleanout or any other top opening. Close And gradually pressurize to 80% of MAWP. <<>> TTMA RUCK TRAILER manufacturer Tank Conference ssociatio TTMAnet.org Since 1941 Jeffrey M. Sims • President 7001 Heritage Village Plaza • Suite 220 • Gainesville, VA 20155 • 703-549-3010 TTMA Position on MC 307 to DOT 407 Venting Upgrades Updated December 17, 2015. ABSTRACT TTMA summarizes the history and rationale behind the venting changes made when DOT authorized new 400 series cargo tanks. The HMR allowed owners of older cargo tanks to upgrade their venting systems to the new code, and the industry embraced this. However, a small minority of users have some confusion, both about what the HMR requirements actually specify and what is best practice. This paper describes the requirements as laid out in the HMR and in official code interpretations from DOT. BACKGROUND The Truck Trailer Manufacturers Association (TTMA) is an international trade association formed in 1941 representing approximately 90% of the trailers manufactured in the United States. TTMA works closely with both regulators and end users. In September of 1990, Docket HM-183 was advanced and the Code of Federal Regulations was modified for construction of cargo tanks. Prior to 1990, DOT had spent a number of years investigating the design, construction and safety of cargo tanks hauling hazardous materials. The old Motor Carrier (MC 306, 307, 312) codes would not be used for cargo tank construction after September 1, 1995. All cargo tanks would be constructed to the new DOT 407 code, three notable differences were: • Removal of fusible and/or frangible disc from the pressure relief system. • Set to discharge changed from (MAWP to +10%) to (120% to 132% of MAWP). • Flow rate calculation threshold shifted from 130% of MAWP to 150% of MAWP. In reviewing actual performance of cargo tanks, DOT concluded the safety record of tanks could be improved. For venting, the MC codes were designed primarily around preventing catastrophic failure of the tank. However many accidents didn't involve catastrophic scenarios, but were less severe (more common) sorts of events; for example, a tank rolling-over on a highway exit ramp. In these events, the design of the MC code venting allowed release of product - when it could possibly have been prevented. Changes were put forward to continue to provide catastrophic levels of protection, while also increasing cargo retention in less severe incidents. Fusible and frangible devices as stand-alone pressure relief devices were removed from cargo tanks (about) 25 years ago. This was done to provide improved containment of the hazardous materials. Industry embraced this change, and it has been a great improvement to the cargo tank design. The set-to-discharge pressure range was increased a slight amount from MC 307 to DOT 407. This increase in pressure range does not have any negative affect on the structural integrity of the cargo tank, since both designs are subject to test pressures of at least 150% of MAWP. The higher set-to- <<>> discharge pressure allows for variations and hysteresis within acceptable limits of use. This change allows the pressure relief device to reseat and seal before dropping below the MAWP. Both of these changes serve to contain the product in the cargo tank in the event of a rollover far better than the earlier designs. In a rollover, a fusible or frangible device that had opened could allow the entire cargo to escape the tank. The increased set-to-discharge pressure served to protect the tank from discharging when the weight of the cargo (head) was added to any internal pressure (when the tank was inverted). CHALLENGE The HMR allow for pressure relief devices to upgraded to the newest specification in §§180.405(c)(2) and 173.33(d)(3). Thousands of MC 307 cargo tanks were produced between 1990 and 1995 with DOT 407 compliant vents. Moreover, many owners of older cargo tanks from the MC 307 years desired an upgrade to newer pressure vents. WHY? Industry didn't want to maintain the older style of cargo tanks with fusible devices that needed to be constantly replaced. They wanted to be environment friendly with robust re-closing pressure relief devices. It made sense then and still does today. They wanted higher flow rates from the DOT 407 pressure relief devices. On the other hand, some groups have misconstrued or misunderstood the wording and intent of the changes to the Code of Federal Regulations. Their misguided interpretations would allow fusible devices back on MC 307 cargo tanks with DOT 407 compliant venting, along with greatly reduced pressure relief devices. Seemingly, they don't understand the applicable engineering principles. Will the design of the MC 307 cargo tank be compromised in any form or fashion if the set to discharge pressure is increased by 10%? Should the flow rates be calculated at 130% or 150%? Both of these questions are technical in nature and are answered best by design certifying engineers familiar with cargo tank design and construction. UNDERSTANDING THE DESIGN Fusible and/or frangible device background: Fusible vents have been used on cargo tanks since the 1950's. Typically, a fusible device consists of a threaded connection holding a fusible element and a disc. The fusible device is designed to yield at an approximate temperature of 250°F. The fusible device communicates with the vapor space of the tank. In a fire emergency, the fusible element would melt and provide an outlet for vapor pressure to escape from the tank vessel. In a catastrophic fire, the boiling liquid could cause a rupture resulting in damage, possible injury and release of the lading. The fusible device creates an inexpensive form of venting the cargo tank's pressure, potentially suppressing the rupture. During the 40 year period from 1950 to 1990 many improvements were made to manufacturing fusible vents. With all of the improvements, the fact remains that this type of relief device is non-reclosing. Once opened, it will stay open until manually replaced. Tank trucks are subject to high shock and vibration loads on a regular basis. Fusible vents are not able to withstand the high vibration load over an extended period of time. When subject to these vibration loads, the fusible vent may open at an 2 <<>> inopportune time. The surrounding environment would then unnecessarily be exposed to toxic, harmful vapors. Heat systems are used on some tank trucks that transport thick viscosity ladings. These heating systems sometimes operate very near to the temperature range that a fusible device is required to yield. The high heat eventually degrades the fusible vent and causes it to open. Another form of adverse heat to the fusible vent is steam from tank cleaning operations. Guidance from DOT: In the 1980's, when DOT was contemplating re-writing cargo tank regulations, they held several public meetings that TTMA members attended. Officials from DOT clearly and succinctly stated their thoughts and intentions regarding fusible devices in the passage, below. In the Federal Register (Volume 50, No.180, p.37776, Tuesday September 17, 1985) DOT stated: 5. We believe that the risk from hazardous material transportation is substantially reduced when packaging is designed to retain the lading in non-catastrophic accidents and to minimize the quantity of lading released when release is inevitable. However in a cargo tank accident, particularly an overturn followed by a fire, the functioning of a frangible disc or a fusible element would result in the release of a substantial quantity of lading. A reclosing pressure relief device on the other hand would minimize the quantity of lading released. Further we believe that a frangible disc and fusible elements particularly in low pressure applications are much more likely to fail as a result of impact and liquid surge than reclosing pressure relief devices. Accordingly, for all cargo tanks constructed after the effective date of the final rule, we are proposing that all pressure relief devices be re-closing except a frangible disc may be used in series with a reclosing pressure relief device. TTMA believes that DOT had a thorough understanding of fusible/frangible devices and focused a great deal of their attention to eliminating the use of non-reclosing devices. This greatly enhances tank safety and protects public interest. How, one might ask? First, when a rollover occurs with an opened fusible device, lading is almost always released; conversely, reclosing pressure relief devices release lading only when there is pressure on the tank. Secondly, the release of non-accident vapors to the atmosphere is prevalent when using fusible devices that have failed due to impact and/or liquid surge. This inadvertent release of vapors is greatly reduced or eliminated with the use of reclosing pressure relief devices. MC 307 Venting systems: 49 CFR 178.342-4, (a) through (d) specifies safety relief vents on MC 307 Cargo Tanks. The device will consist of pressure-actuated spring loaded device, otherwise known as a reclosing safety relief device. When necessary to meet the venting capacity of Table Ill, one or two fusible and/or frangible devices would be added to the total venting system. The spring loaded safety relief device in this system makes up a subpart of the total capacity of the pressure relief system. The fusible or frangible device(s) are used to augment this system. DOT 407 venting systems: 3 <<>> 49 CFR 178.345-10 (a) through (h) specifies the requirements for DOT 406, 407 and 412 series pressure relief system. Specifically, 178.345-10 (b) (1) requires that each primary pressure relief system consist of one or more reclosing pressure relief valves. Furthermore, non-reclosing (e.g., fusible disc) pressure relief devices are not authorized in any cargo tank. The venting capacities from Table I will require one or more reclosing pressure relief devices. Note: reclosing pressure relief manufacturers were able to meet the higher flow requirements of 178.345-10 by changing the design pressure of the relief device, increasing the flow rates by up to 10 times. The clear intent by the DOT was to remove any fusible and/or frangible disc from trailers hauling hazardous cargo, due to safety concerns for the general population. Upgrading MC 307 to DOT 407: There are three different sections of code that address upgrading MC 307 cargo tanks to DOT 407 cargo tanks. §173.33(d) (3) specifies that the pressure relief devices may be modified from MC 307 to DOT 407. Again, $180.405 (c) (2) states that an MC 307 cargo tank may have its pressure relief devices modified to conform to the DOT 407 specification. Lastly, §180.405(h) (3) says the owner of a cargo tank may elect to modify reclosing pressure relief devices to more recent cargo tank specifications, however it must provide minimum venting capacity required by the original specification. The Federal Government clearly wanted cargo tank owners to willfully consider upgrading MC 307 pressure venting systems to DOT 407 code. None of the three cited codes suggests leaving fusible vents in place, nor does it mention having to update the set to discharge pressure from 120% of MAWP to MAWP, or calculating the flow rates at 130% of MAWP. Instead, they clearly state how to upgrade the pressure system to the new code requirements. While some have misinterpreted the caution to ensure that upgraded vents have sufficient capacity to prevent cargo tank rupture as meaning that the pressure vents must be rated at the original pressures, this was settled when the DOT issued an interpretation dated June 10, 1996 and signed by Hattie L Mitchell which said: -Specifically, you asked if §173.33(d)(3) prohibits upgrading vents on MC 307 and MC 312 cargo tanks to DOT 407 and DOT 412 vents that are flow rated in accordance with §178.345-10. 000 The answer is no. ... HOW TO MEET THE REQUIREMENTS Fusible devices shall not be employed on cargo tanks with DOT 400 series compliant venting, including MC 307 units. The results are evident! There is a much lower non-accident release record. Lading is not being poured out needlessly when trucks are involved in rollover accidents without explosions. Toxic vapors are not being released to our atmosphere. Set-to-discharge requirements of the DOT 400 series venting regulations are easily met. The increased tolerance range of 120% to 132% MAWP is easier to qualify during bench testing, the possibility of set- 4 <<>> to-discharge going under the MAWP has been eliminated, and reseat (or reseal) of the pressure relief device occurs before reaching MAWP. The change in set-to-discharge pressure does not have adverse effects on the structure or integrity of the shell design for the cargo tank. As a general physics statement, mass flow proportionally increases with pressure. During a catastrophic event, a rapid temperature rise will consequently increase flow rates. The older, outdated pressure requirement of 130% to MAWP for the mass flow calculation has been abandoned. All transportation industries embrace the updated flow pressure requirement of 150%. This calculation is applied to trains, ships, and other forms of transporting hazardous materials. TTMA fully embraces this shift and sees no reason to apply an outdated standard to cargo tanks. TTMA has noted an untarnished safety record for upgraded MC 307 cargo tanks using the modified DOT 407 pressure relief systems over the past 25 years. This track record stands by itself. Thousands of cargo tanks have been built and continue to be in service using this system, working safely, as intended. ABOUT THE USERS WHO HAVE MISINTERPRETED THE UPGRADE REQUIREMENTS TTMA is aware of some people advancing the idea that pressure relief devices, especially those on MC 307 cargo tanks cannot be upgraded to DOT 407 vents set and flow rated according to the DOT 407 requirements. This small group of users continues to operate cargo tanks with the misunderstanding and misinterpretation that requires a fusible device and flow rate calculations at 130% of MAWP. They feel it is the only way to be in complete compliance with the code. However, by applying pressure relief devices that are set and flow rated according to the original specification, they have simply forgone upgrading. They are operating their cargo tanks with pressure relief meeting the requirements when the cargo tank was built as provided for in 173.33(h)(2). They do not necessarily gain the benefits of having better lading retention and fully reclosing devices of the DOT-400 series requirements. TTMA does not recommend mixing devices: A DOT-407 venting system is not designed to be operated in conjunction with non-reclosing vents alongside it. DOT's intent was to eliminate non-reclosing devices to maximize retention of hazardous materials, and allowing fusibles to continue to operate on otherwise upgraded systems would be contrary to that mission. Further, this is most often done due to operator error: There is no need to provide a fusible vent alongside DOT 400 series reclosing device as these are adequately sized to provide sufficient flow to protect the cargo tank from rupture. CONCLUSIONS The clear intent by DOT is to have all fusible devices removed. Neither the integrity of the MC 307 cargo tank, nor the pressure relief system will be degraded - if the set to discharge pressure is increased from MAWP to 120%. It is a correct interpretation of the CFR - and also safe - to install DOT 407 pressure relief devices on MC 307 cargo tanks. Lastly, a calculated flow rate of 150% of MAWP is a standard used throughout transportation industries around the world. 5 <<>> TTMA TECHNICAL BULLETIN TRUCK TRAILER MANUFACTURERS ASSOCIATION 8506 WELLINGTON RD. / SUITE 101 (703)549-3010 MANASSAS, VA 20109 www.ttmanet.org TB No. 126 November 15, 2012 Title: Bench Testing Reclosing Pressure Relief Devices Previous Editions: Originally issued November 2012. 1.0 Preface: 1.1 No part of this document may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system without written permission from the Truck Trailer Manufacturers Association. 1.2 Recommended Practices and Technical Bulletins are furnished by the TTMA as a guide to general practices Practices and Technical Bulletins is not exhaustive of all general practices in the manufacture, use, and in the manufacture, use, and repair of truck trailers. However, the scope of the TTMA's Recommended repair of truck trailers and there may exist such general practices which do not appear in either the 1.3 Recommended Practices and Technical Bulletins represent the state-of-the-art that existed at the time of its advancements in practices that have occurred subsequent to the Recommended Practice's or Technical preparation. Users of Recommended Practices and Technical Bulletins should familiarize themselves with 1.4 Practices or Technical Bulletins may be used by manufacturers, users, or repairers of truck trailers nor the The TTMA has not undertaken any evaluation of all the conceivable ways in which Recommended consequences of such uses. Everyone who uses Recommended Practices or Technical Bulletins must first other equipment will not be jeopardized by their use of information contained within the Recommended satisfy himself or herself that his or her safety, the safety of others, or the safety of the truck trailer and any 1.5 meanings. Definitions for such terms or words may be found in TTMA RP No. 36 - Tạnk Trailer and Tank The Recommended Practices and Technical Bulletins may contain terms or words with specializer Container Nomenclature or TTMA RP No. 66 - Trailer Nomenclature. 1.6 1.7 Cod any no won formity public to ply cations is ner dead or tie non-conck ming pis ted being. 1.8 Any inclusion of R - **truncated:** true - **body characters:** 51157