The Transportation of Dangerous Goods (TDG) Directorate of Transport Canada (TC) is the focal point for the national program to promote public safety during the transportation of dangerous goods. The TDG Directorate serves as the major source of regulatory development, information, and guidance on dangerous goods transport for the public, industry, and government employees in Canada. The Safety Research and Analysis branch of the TDG Directorate supports this mandate by studying various aspects of the transportation system to inform decision-making processes.
The TDG Directorate is undertaking a project to analyse past incidents where the vent and burn technique was executed and subsequently failed, to determine if there are any possible solutions that can be considered, based upon the existing research on this topic that was carried out over 20 years ago. From 2004 to 2006, TC-TDG and its partners conducted tests using commercially available shaped explosive charges on highway tanks to further develop the last resort technique known as vent and burn. The outcomes from this previous research project can be found here: https://tc.canada.ca/en/dangerous-goods/last-resort-v… This technique is used to prevent a catastrophic tank failure or an uncontrolled release of liquefied petroleum gas (LPG), or OTHER liquefied flammable gases in the environment during an incident, when no other remedial measure is viable. Current practice for this technique involves placing shaped explosive charges on the top and the bottom of a large means of containment (MOC) (e.g. highway tank, tank car). The detonation of the shaped charges at the top of the tank and simultaneous ignition of the escaping pressurised vapour contained within the vapour phase, will decrease the likelihood of catastrophic failure by reducing the high internal tank pressure. After a pre-determined, usually short, time delay, this step is followed by detonation of the shaped charges on the bottom of the tank, which will allow the liquefied portion of LPG to drain out of the tank into a drainage area for a controlled burn.
The placement of the shaped charges on the MOC containing the liquefied flammable gas is done by hand by trained professionals. In the event of an incident where a vent and burn is necessary, there are multiple factors that can make this task more hazardous, other than the risk of MOC failure. Circumstances that can increase the hazard include, but are not limited to, the number of tanks involved, the dangerous goods in each MOC and their incompatibilities with each other, the risk of BLEVE (boiling liquid expanding vapour explosion) of the tank(s), the presence fire, or the spatial orientation of the tank cars (i.e. the vapour or liquid phases of the tank may not be accessible without removal of debris, or may not be accessible at all).
Although the vent and burn technique is used very seldomly, there may be options for increasing the safety for those involved in executing it, by remotely placing the shaped charges on the tank. This may allow for use of the technique in a wider array of incidents by increasing the safety for the explosives technicians performing it and provide guidelines to help inspectors or remedial measures specialists (RMS) determine if they should intervene as per section 19 of the Transportation of Dangerous Goods Act, 1992.
To examine potential improvements in safety requirements and inform emergency response procedures for liquefied flammable gases, the TDG Directorate requires the services of a contractor to conduct a literature review, technology scan and evaluation, and subsequently a feasibility analysis regarding the remote placement of shaped charges during the vent and burn technique. In addition, consultation with appropriate experts on the technique should be conducted to supplement the information found in the technology scan, as appropriate and gather firsthand experience that may not have been published. This will enable the TDG Directorate to provide recommendations with an aim to increase safety of operators performing vent and burn procedures, as well as allow for potential revisions of the current technique.
