A Chemist on Reddit Just Explained What May Have Caused China's Deadly Explosion

Earlier this month, two explosions engulfed the warehouse district of the Chinese port city of Tianjin, killing at least 129 people. Though we know the explosions followed a large container fire at a warehouse where dangerous chemicals were stored, the details of what exactly happened are still under investigation.

On Tuesday, chemist May Nyman, a professor at Oregon State University who studies inorganic materials, hosted an AMA on Reddit to answer questions on what we know about the blast, and provide some expert insight into what might have happened. Here are the most illuminating questions from redditors and Nyman's responses:

What is your hypothesis for an explanation of the explosion?

Thank you for using the word hypothesis, because that is indeed all we can do here. My biggest suspicion is the calcium carbide was a starting point, because it is so reactive with water. Water is everywhere—it's in the air (i.e. relative humidity is a measure of how much water there is in the air). If the calcium carbide is accidentally exposed to water through a hot humid day in an uncontrolled climate, a leak, a damaged container, it will start to react. Acetylene is flammable and provides pressure, and could have been the source of the fuel for the fire.

That being said, it seems there should have been a spark that started the fire—human or instrument error, the same way forest fires start—a discarded cigarette or an electrical spark from a faulty wire or electrical cord.

What, if any, long term effects do you anticipate for the area?

This is a great question. The good news is, much of the chemicals present in the warehouse likely got destroyed in the two massive explosions. Anything organic converted to carbon dioxide, water and some form of nitrogen oxide. So large amounts of these gases, which are generally not harmful, could result in some changes in the local environment. For example, excess carbon dioxide could get into the water and make it acidic, but the ash could make the water basic so it is difficult to say the final result. Nitrogen oxide can be dangerous in numerous ways.

The other, more long-term effect could be the chemicals that did not get completely destroyed, but instead released, due to damage of the facilities or their containers. For example, toluene diisocyanate is reported to be stored in the warehouse. This would alter its form in water, but convert to molecules that could last a long time in the environment (something like benzene).

In April 2013 a fertilizer plant in West, Texas exploded when firefighters sprayed water onto a burning warehouse full of ammonium nitrate. It killed my cousin, who was one of those firefighters. The Tianjin explosion seemed very similar to me. Were the same chemicals being stored in Tianjin?

Another good question. Ammonium nitrate was reported to be present in the warehouse. Ammonium nitrate itself is not explosive nor reactive with water. But it is shock sensitive and can explode, when hit with a violent force like that of a powerful water stream, or some other chemical explosion nearby. It can also react with the some other released gas like the acetylene from the calcium carbide. It can also release ammonia which is dangerous.

Again, I emphasize, many chemicals combined, stored close together in a warehouse, is a recipe for disaster, and different reactions can trigger other reactions.

Dead fish wash up near Tianjin explosion site, according to Beijing news. pic.twitter.com/whPccHU55I
— Dali L. Yang (@Dali_Yang) August 20, 2015

Could you elaborate a little more on the fish dying and the soap sud rain?

These phenomenon are indeed curious. If we think about such a large explosion, what results is lots and lots of ash. Ash is in fact the ingredient for making soap, the old-fashioned way. Ash and water makes lye (very alkaline water) which could react with road tar or oil, and you could get a very crude soapy material.

Now about those fish. The pictures of many dead fish are pretty shocking. Again, ash produces alkaline water, so perhaps it could be the alkalinity in the water went up (acidity went down), this is not the fish's usual environment, which resulted in massive death. And also, per a comment below, there are times of the year that water does not get so much oxygen, algae blooms, etc. which could result in pressure on the fish's environment and result in death.

I currently live in Shanghai. It has been rainy here and I've heard reports that the weather could be contaminated with smoke from the blast. Is there anything to worry about?

Smoke from a huge fire like this can travel thousands of miles easily, and is controlled by weather patterns. However, at that point, smoke is smoke. Similar from a chemical fire or a forest fire. Especially if it has traveled such a long distance. So it could certainly contribute to making the air quality worse in Shanghai, but that should be only very temporary.