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Given the frequent incidences of Non-Accident Releases (NARs) of hazardous materials from tank cars, there in an increasing interest in transporting hazardous materials in total containment conditions (i.e., no pressure relief devices). However, the ability of tank cars to meet thermal protection requirements provided in the Code of Federal Regulations under conditions of total containment has not been established. Also, the modeling tool commonly used by industry to evaluate thermal protection, AFFTAC, has not been validated under these conditions. The intent of this effort was to evaluate through a series of third-scale fire tests, the ability of tank cars to meet the thermal protection requirements under total containment conditions, and also, to validate AFFTAC for such conditions.
This paper describes the test design and planning effort associated with this research, including the design and evaluation of a fire test setup to simulate a credible, fully engulfing, pool fire that is consistent and repeatable, and the design and hydro-static testing of a third-scale tank specimen. The fire design includes controls on the spatial distribution and temperature variation of the flame temperature, the heat flux, and the radiative balance, to best reflect large liquid hydrocarbon pool fire conditions that may be experienced during derailment scenarios.
In North America certain hazardous materials are transported in rail tank cars that must be able to survive an engulfing liquid hydrocarbon pool fire for 100 minutes without rupture. To meet this requirement these tanks are normally equipped with pressure relief valves (PRV) and some form of thermal insulation or thermal protection (TP).
These tanks sometimes have non-accident releases (NAR) due to unwanted activation of, or leakage from the pressure relief valves (PRV). These NARs are a nuisance for Industry and for this reason, the industry now wants to remove the PRVs from certain tanks. This is known as total containment and is common practice in Europe. However, Europe does not have a 100 minute fire survival requirement. This paper is about a series of fire tests of 1/3 rd linear scale US DOT 111 Tanks cars. The 2.4 m3 vessels were subjected to fully engulfing fires generated by liquid propane fueled burners.
Pressurisation of full-containment pressure vessels in fire is known to be driven by thermal stratification. The predominant mode of heat transfer to the contents (convection from the shell to the liquid phase) results in formation of „hot“ boundary layers. Sub-cooled boiling may also be present. The warm layer rises to the surface through buoyancy and bubble flow, increasing the surface of the liquid above that of the bulk temperature, and hence driving a pressure rise.
For reliable prediction of the complex effects governing vessel pressurization a three-dimensional numerical model is required. Work is being undertaken on such a model by other institutions in cooperation with this project.
An overview of test standards and regulations relevant to the fire testing of pressure vessels
(2021)
Fire exposure of storage and transportation vessels of hazardous materials (including pressure liquefied gases) can result in BLEVEs and other high-consequence incidents with large societal and economic impacts. To reduce risk most countries have numerous regulations, codes of practice and guidance notes covering the design, operation and maintenance of vessels and thermal protection systems. Yet despite such regulations there remains no internationally accepted fire test procedure for pressure vessel and accompanying thermal protection systems that is capable of meeting a range of regulatory requirements. This paper considers some of the regulations in place in the western world and considers the origin of these based on large and medium-scale testing conducted to date. It examines conditions found in these tests to propose a set of recommendations on which to base a standard method of test. These recommendations are proposed as being representative of a credible large pool fire scenario that may occur.
A novel deign of test equipment has been commissioned to investigate thermal stratification and boiling during fire exposure of pressure vessels. Extensive temperature measurements and video of the internal conditions during fire exposure are possible, and the equipment has been designed for future compatibility with laser-based velocity measurement techniques. It is expected to generate data large quantities of data that will be of use in validation of two- and three-dimensional CFD models for the prediction of pressure vessel behaviour in fire. Future work will seek to characterize the boundary layer conditions in detail for a range of test fluids, fill levels and fire-induced thermal boundary conditions.
Initial tests undertaken during commissioning may indicate that fire exposure of the vessel wall just above the liquid level can have a notable influence on the pressurization rate, by increasing the degree of superheat. Further experimental and modelling work is required to confirm and quantify this effect, or to rebut this conclusion.
We are interested in accidental fire impingement of HazMat pressure vessels. Want to develop improved models for predicting time to failure or empty (if PRV present). We are still trying to properly predict pressurization and time to first PRV activation due to liquid temperature stratification for a range of fire scenarios (Full and partial engulfing pool fire, jet fires, with roll over, with TP defects, etc.)
Full engulfment fire tests have been conducted on total containment pressure vessels filled to 50% and 98 % capacity with water. The tests included an unprotected tank and tanks with two different levels of thermal protection. Total containment in this context means there was no pressure relief device. The tests were conducted with 1/3rd linear scale rail tank cars similar to the DOT 111 tank cars used in North America. The 2.4 m3 model tanks were subjected to 100 % engulfing fires fuelled by liquid propane. The fire heat flux was approximately 80 % by radiation and 20 % by convection with a total heat flux to a cool surface of approximately 100 kW/m2.
The US Department of Transportation, Federal Railroad Administration (FRA) current regulations for rail tank cars in the United States stipulate that, for certain hazardous materials, tank cars shall have a thermal protection system capable of preventing rupture of the tank for 100 minutes when exposed to an engulfing fire with a blackbody equivalent flame temperature of 871 °C (+/- 56°C), and that tanks shall have a pressure relief device set at an appropriate level (depending on the type of tank car and contents). Pressure relief devices are a source of non-accident releases, and hence may cause serious incidents when tanks are transporting hazardous materials. Industry in North America would therefore benefit from removal of pressure relief devices on tanks transporting certain hazardous materials. Such an approach is known as full Containment, and is standard practice in Europe. In 2014 the FRA commissioned an experimental study to investigate the ability of a specific design of rail tank to resist rupture without incorporating a pressure release valve. As a precursor to tests on tanks there was a need to develop and characterise a simulated pool fire capable of reliably exposing large-scale tanks to repeatable, uniform conditions. This paper describes such a fire test setup, developed using a burner array system fuelled by liquid propane and designed to produce luminous, low velocity flames representative of those found in large hydrocarbon pool fires. The experimental set-up is described, along with the Instrumentation (directional flame thermometers, infra-red camera, and thermally massive calorimeter) and methodology used to characterise the fire. Comparisons are made against previous fire tests on vessels to assess the suitability of the experimental set-up for future vessel testing.