In the last article we discussed several types of trailers; the flatbed trailer, dump trailer and box trailer. The box trailer is one of the most common and the most difficult to predict when working a crash scene. We seldom know at first assessment what is in the truck and how much it weighs. We can make a better judgment call on a flatbed or dump trailer. With those being open to a degree, we can see what they are hauling. Another somewhat common trailer is the tanker. With proper hazmat training, and the trailer being placarded correctly, we will know what it could be hauling. The big question is, do we know how much it weighs if loaded? What if it is partially loaded? Partially loaded tankers can shift if the contents have been moved to one end or the other, or to one side. During our assessment we have to consider what the contents may weigh and where that weight is now displaced. Most tankers have baffles internally so when the tanker is not full, and the contents are moving back and forth during transport, the shifting will not become an issue while traveling down the highway. With the trailer on its side or at an angle, the contents will now travel to the lowest point and that is where the weight will be concentrated. Shifting the tanker while lifting it, may move the contents and change the entire dynamics of your vehicle, and now the weight may be concentrated somewhere else. Something that would need to be accounted for and that will be discussed in a future column.
Just for giggles, had to leave the other word out, this is a “G” rated publication, let us look at several materials that are hauled in these tankers and what the weights may be. We will take water as a starting point at 8.33 pounds per gallon. A 2500-gallon tanker full of water will weigh 20,825 pounds, not including the weight of the tanker. This is something most firefighters are familiar with as the tankers in your station haul water. The weight of all liquids will be based on the density of the fluid itself. The more the molecular concentration, the heavier the material will be. Now, we will look at gasoline, diesel fuel, Liquid LPG, crude oil, liquid asphalt, 10% Hydrochloric acid and milk. Before you read any further, and don’t cheat, which of these fluids do you think weighs the most per gallon and which weighs the least? Remember to think about the density.
Gasoline comes in at 7.29 pounds per gallon, which we all know that gasoline is lighter than water. What about diesel fuel? The first thought is that it appears to be thicker than gasoline so it would weigh more than 7.29 pounds per gallon. Contrary to that, diesel fuel weighs slightly under gasoline at 6.953 pounds per gallon. Light crude oil, one that you would think as being heavier than gasoline, comes in at seven pounds per gallon, just under gasoline. What about liquid propane, heavier or lighter than gas or diesel? Liquid LPG is quite a bit lighter than gasoline and comes in at 4.23 pounds per gallon and is the lightest on our list. So if you guessed LP for the lightest, you were correct. Most guess that liquid asphalt is the heaviest of the list, and the surprising fact is, it is only .01 ounce heavier than water per gallon. It comes in at 8.34 pounds per gallon, the heaviest yet. Hydrochloric acid at 10 percent weighs 6.42 pounds per gallon, but as the concentration of acid increases, so does the weight. HCO at 38 percent would weigh 9.9 pounds per gallon. Milk, which does a body good, weighs 8.6 pounds per gallon and if you guessed this as the heaviest, you were right.
The point of this little exercise is that, although fluids have different densities and molecular structures, and weigh in at different amounts, you can still come close on your assessment of the crash scene. If you noticed, most of the materials were fairly close in weight. If you calculate your contents and loads based on eight pounds per gallon, you will be close in most all cases. Knowing the size of the tanker is also crucial to your calculations, with most ranging around 5000 gallons. The real trick is in knowing how much material is on board. If the driver is conscious, then that information will be easy to come by, just ask. If he has made some drops, he can let you know. If the driver is not able to give you any of that information, then always lean on the side that the tanker is full and go from there, until you determine otherwise. Always better to overestimate the load and stabilize for it, than to underestimate the load and have a failure occur.
Next time we will continue to discuss other aspects of heavy vehicle rescue. When a heavy vehicle rescue class comes available, consider enrolling and taking it. Nothing like getting the chance to do some hands on work. I hope everyone’s holidays are good, as it will be after that before the next column hits the Journal. Be safe out there and train to be the best you can. See you next time.