Comparing Rail and Pipeline Safety
Incidents as a Determining Factor of Safety
There has been a lot of discussion by industry analysts, governments, government agencies and the general public about rail versus pipeline safety for transporting crude oil. On balance, the perception among these groups appears to be that pipelines are safer than rail for moving crude oil.
Some of this perception comes from a study by the Fraser Institute citing that pipelines are safer than rail because rail has more incidents with releases than pipelines. Using only the number of incidents to arrive at this conclusion, one would have to assume that all incidents are equal in spill volume and distance travelled which could hardly be true. This flaw in the comparison has led to the unwarranted conclusion that pipelines are safer than using rail.
An other study by Oliver Wyman resolves the issue by combining three incident elements into an Incident Rate as shown below:
- The total volume of crude spilled by each mode (annual gallons)
- The total volume each mode transports (annual gallons)
- The total distance the crude oil is moved (annual miles)
Incident Rate = Number of incidents / (total volume x total miles)
The result of this normalized unit of measure can be seen below.
|Source: Oliver Wyman and Railway Association of Canada, Canadian Crude Oil Transportation, Comparing the Safety of Pipelines and Railways, December 2015|
|10Statistics Canada, Table 133-005, Operating Statistics of Canadian Pipelines Carriers; Railway Association of Canada; Oliver Wyman analysis.|
|11 Note table excludes pipeline volumes and incidents for February 1 to June 15, 2013, due to the lack of availability of Alberta incident data during the transition of incident monitoring responsibility from the Energy Resource Conservation Board to the Alberta Energy Regulator.|
Another way to look at making a direct comparison can be found in the Fraser Institute’s study. The table below from this study shows the release gallons per billion ton-miles of rail, pipeline and road modes. This is a nominalized unit of measure for comparison. Based on that metric railways release 3,504 gallons compared to 11,286 gallons for pipelines. On that basis, pipelines spill 3.2 times more oil than rail.
If the conclusion about whether one mode is safer than another is based on spills, then the conclusion would be that rail is safer than pipelines.
Comparing Crude Oils Transported by Pipeline and Rail
The term crude oil is used broadly in the public discussion. However, there are a wide variety of crude oils with varying characteristics based on density (or API), flashpoint, sulphur content and many other items. An industry website Crudemonitor.ca lists many of these characteristics. Further detailed discussion about the properties of western Canadian oil can be found on the Alberta Innovates website here.
Generally, the literature revolves around oil that meets specifications for shipping in a pipeline; an example of which for Enbridge can be found here. Typically, the specifications are that the density of oil at 15C can not exceed a density of 940kg/m3 (or ~19 API) and kinematic viscosity of 350 cSt (or how sticky the oil is).
|Video: Diluted Oil - Pipeline Specifications|
Because oil is pushed long distances through the pipeline, it has to flow well which is why it can’t be too sticky (low viscosity) or too heavy (too dense). Lighter crude oils will flow easily but heavy crudes are too sticky and dense and have to be diluted with a condensate (a volatile, low flashpoint, light hydrocarbon referred to as a diluent).
When heavy crudes are diluted with a diluent, the mixture is called dilbit. Generally, the ratio of diluent to heavy crude is about 70% oil, 30% diluent. While this lowers the viscosity of the oil (makes it less sticky) it also greatly lowers the flashpoint of the original heavy crude.
Flashpoint is the lowest temperature where enough fluid can evaporate to form a combustible concentration of gas. The lower the flashpoint of the oil the easier it is to ignite.
The flashpoint of a conventional heavy crude is about 150C. Heavier crudes such as bitumen will range much higher to over 200C. In contrast, diluent flashpoints are typically less than -35C. A 150C flashpoint heavy crude mixed with a -35C flashpoint diluent on a ratio of 70% - 30% will result in the dilbit mixture having a flashpoint of about 20C (or slightly less).
Since a normal room temperature is about 20C, this means that this dilbit mixture would give off ignitable vapours at about room temperature.
Rail transport has no specifications for the product itself. It does not matter about the density, viscosity, water content or anything else as it relates to the physical movement of the product. That’s because the product is contained within a rail car. The rail car moves on the tracks and carries the oil with it. The rail car is analogous with diluent in that they both “carry” product in their transportation modes.
The Less Diluent the Better for Rail and Overall Safety
The economics of shipping crude using rail depends on there being little to no diluent in the oil. Therefore, industry is driven by economics to not add volatile diluent to rail crude oil shipments. The vast majority of the crude oil shipped by Altex contains no diluent and is pure heavy crude in the range of 986 kg/m3 (or 12 API) and a flashpoint in excess of 150C. Altex has shipped some “under diluted” crude oil having about 12-15% diluent. This is under diluted mixture is sometimes called “railbit”.
Should a rail car rupture, undiluted heavy oil will not flow quickly at room temperature as the video above shows. Any oil leaking from the rail car will be thick and sticky and will not produce any explosive vapours.
Video: How Heavy Oil Flows When Diluted and Under Pressure
Since the car is not under pressure, the oil will tend to stay in place rather than flow into the environment as diluted oil would and especially when diluted oil is under pressure as it is in pipelines.
Therefore, transporting undiluted oil is inherently safer than diluted oil because it won’t create ignitable vapours at typical outside temperatures and it will tend to want to stay in place should there be a spill.
A more balanced conclusion, as shown by the data, is that both railways and pipelines are very safe modes of transport for crude oil. And while the goal is always to have zero releases into the environment, both are very near zero especially when viewed from the amount of crude oil moved over the distance travelled.
When looking at the type of oil moved, heavier crude oils are suited to move by rail since they do not need to be diluted and hence are far less volatile and will not easily escape into the environment. Lighter crude oils are suited to move by pipeline since they can flow easily in a pipeline without dilution.