Tank wagon classes A and B and the differences

We are currently restoring Esso 1855, and we often refer to it as a Class B tanker. But What exactly is a class A or B Tanker? 

What is a tank wagon?

It is worth defining what a tank wagon actually is. A tank wagon is a railway wagon with a tank mounted to it that is designed to carry and transport either a gas or a liquid product. Products like milk, water, petrochemicals, ammonia, oils, LPG, acids, and even beer are all (or once where) transported by rail in bulk and there are many other products.

Certain products require certain handling, so typically, one wagon will carry the same product for its entire working life – unless it is modified to transport something else. Changing the goods a tank can carry would require cleaning, decontamination and possibly modifications (heating and insulation) to carry another product.

A set of the same type of wagon will typically transport multiple wagon loads of the same product, at least in the UK. Mixed freight operations are less common in the UK. You can have containerised tanks, but these are not dedicated tank wagons.

Class A or B

Certain goods need particular care to move them around. Buying eggs from the supermarket requires a different level of care than a tin of soup, and we know this because of a few broken eggs. Goods capable of a knock go in the bottom of the bag, eggs and tomatoes in the top. 

The rail industry faces this problem every day, and when 1855 was new, the classification system existed to divide suitable goods into two categories. Class A and Class B. What separated these 2 classes was the flash point of the material to be transported. 

What is flash point? 

The flash point of a material has quite a lot of detail, and this article explains all of the details about the flash point but for simplicity the flash point is the lowest temperature at which the vapours of the material can ignite. 

So petrol has a flash point of -43°C, Diesel is greater than 52°C and Kerosene is 37°C. Vegetable oil a flash point of 327°C.

That means that, below those temperatures, the vapours of those mixtures will not catch fire. Anything above those temperatures, a risk of serious fire and explosions exists if there is a naked flame. 

This is why it was common to see certain tank wagons with the phrase “NO NAKED LIGHTS TO BE BROUGHT NEAR” because the risk of vapours and the flash point is a real danger.

Class A and Class B flash points

We know that classes A and B were defined based on the flash points, but what exactly are those? 

Your material was considered class A if the flash point of the material was below 23°C (That is about 73°F). 

It would have been considered class B, if it was 23°C or above but below 60°C. 

Some examples of class A products include petrol, ethanol, acetone and jet fuel. Some class B products include diesel, kerosene, bitumen and certain lubricating oils. 

Heavy fuel oil was considered a class B product even though its flash point was above the upper class limit because HFO was transported in a heated state. Many wagons, including 1855, were fitted with steam coils and heating to reduce the viscosity of the product to make it easier to discharge. This increased the risk of the product. 

Each class had their regulations 

Once the class of regulation was known, the handling and transport of the goods were then regulated by the class. 

Pre World War 2, class A wagons were ordered to be painted in a light stone colour with a red band around the halfway point of the tank wagon. The fabrication, size and chassis were also regulated by the RCH. Early into the war, the light stone regulation color was dropped. 

Class B tankers were typically painted black to hide spillages as most class B products were oily and left stains. 

Both classes had limitations on the maximum distance and speed they could travel without stopping (it changed over time), and they must be stable over those distances. We will cover that in a future article. 

For a long period, it was a requirement that tank wagon sets must have 2 non-tank wagons before and after the set of tanks to act as a safety measure. 

How this impacted many tank wagons after the war 

Many tank wagons commissioned for World War 2 were produced as Class A wagons. The airfields needed jet fuel to keep the planes in the air, but after World War 2, the demand dropped. 

This meant that many wagons were modified to support class B products. Many, like 1855, were painted entirely black and had steam heat fitted and bottom discharge. Bottom discharge was banned in class A tanks, so wagons with it were fitted in a conversion process after the war. 

What about milk?

If you had a product with a flash point above the limit of a class B product, it did not fit into either class, so the petrochemical regulations did not apply to the product. This was quite smart because it allowed the regulations to be product-independent and entirely property-dependent. They didn’t regulate the product; they regulated the properties of products. 

These regulations did not apply to your local dairy, and you would have had to comply with other regulations.  Food products would have required their own temperature and other environmental controls and would have had their own set of regulations that dictated their handling. 

Milk wagons would have required stainless steel tank construction, weight restrictions (as noted by the extra wagon), speed and travel restrictions and insulation for thermal controls.

Does class A and B exist today? 

While it may seem like a small detail, the class designation for these wagons played a crucial role in how goods were transported around the country. However, today, the class system has been superseded by a globally accepted standard of goods. 

With the invention of the shipping container, you could suddenly have a tank in a container, on a container ship that contained sugar syrup, next to another that contained acetone. This meant that you needed a standard which was globally understood by everyone and there is the UN Dangerous Goods Classification that people follow.

While dedicated petroleum tank trains still run, they also have an upgraded set of standards that follow similar protocols and standards as lorries. You can read more about these standards and class designation here.