Reader Comment – Water over Water-Reactive Chemicals

After reading an article on GPB.org about last week’s publication of the Chemical Safety Board’s 2^nd update on the investigation of the September 2024 BioLab chemical fire in Conyers, GA, a long time reader (and one of the few that I have met IRL) asked me for my take on the situation. I have been pondering this response for three or four days now, but I am ready to address this now.

The reason for the delay is that the question about the use of a water fire-suppression system over an area used to store a water reactive chemical really deserves a lengthy technical discussion, covering the reaction mechanisms including the heat of reaction, the reaction rates under various scenarios and the byproducts of those reactions. This would then allow for an informed discussion about the design considerations for the fire suppression system. Unfortunately, I do not have any of that information, and from what the CSB said at the end of their report about what they were continuing to look at in their investigation, neither does the Board.

So instead, I am going to have to address this issue by using a series of analogies.

Add Acid to Water

One of the first-year chemistry safety lessons is summarized by the sentence: “Add acid to water, not water to acid.” Most mineral acids (for example sulfuric acid that I have dealt with frequently in my career) are soluble in water, so why should there be a safety issue about mixing the two. The problem is caused by something called the heat of solution, when mineral acids dissolve in water the ‘reaction’ produces a great deal of heat very quickly (nearly instantaneously for all practical purposes). If you add a drop of water to concentrated sulfuric acid, the heat will be sufficient to turn much of the drop of water to steam with the attendant expansion of the volume. This splatters undiluted sulfuric acid around, potentially injuring the person adding the water to the acid, a serious safety situation to be avoided.

The problem becomes much worse if you take a syringe and inject a stream of a couple of milliliters of water into the same concentrated acid. The force of the stream pushes the water further into the container of acid, resulting in a much larger ‘steam explosion’ that throws a significant amounts of acid further from the container increasing the chance and extent of potential injuries.

However, if you spill a gallon of concentrated sulfuric acid on the concrete in a chemical plant and then hit the puddle immediately with a stream of water from an industrial scale hose, there is no noticeable reaction caused by the heat of dilution. The volume of water is sufficient to spread the heat of solution over a wider area. Knowing the heat of dilution, it is a simple matter to calculate the minimum amount of water needed to safely add water to acid.

Water for Solvents

Another well known safety mantra is that you do not use water to fight fires in organic solvents that are not soluble in water. Since most of these solvents are lighter than water they float on top of water and are likely to spread the fire when water is applied to such fires. I worked in a chemical facility that used small quantities (a couple of drums) of such solvents. Rather than employ expensive foam suppression systems that are usually required to fight such solvent fires, the facility chose to use a deluge water suppression system. These systems use huge amounts of water flood the facility with water to eliminate the issue.

Waterproof Storage

One final thing to consider is that the facility stored the trichloroisocyanuric acid (TCCA) in water resistant storge containers. The material was stored in ‘supersacks’. These are made of an tightly woven plastic bag that sheds water and a water proof plastic inner liner. The twisted closures of the top and bottom openings of the bag are the only thing that stops the supersacks from being truly waterproof, if you submerged these bags in water over a period of time, there might be some leakage. A picture on page 11 of last week’s report shows some of the bags still intact after the walls collapsed over them (and under the further application of firefighting water).

SDS Information

According to the CSB report (pg 4) the TCCA Safety Data Sheet (I have not received a response from BioLab’s spokesperson about my request for a copy of that SDS):

“While TCCA and DCCA are not classified as water reactive per the Safety Data Sheets (“SDSs”), their SDSs indicate that contacting these materials with water or moisture may cause fire or explosion hazards. The SDSs also indicate that it is necessary to flood the area with large amounts of water from a distance to extinguish a fire involving these materials.”

Self-Delusion

With this discussion in mind, I can see how the owners convinced themselves that the design of the water fire suppression system for the Conyers, GA, facility would be a safe system. Having said that, there is an interesting quote from the GPB.org article:

““I brought up questions about 'Why do we have a water-based fire system over water-reactive chemicals?'” Garcia told GPB. “I brought the risks that could come about, but we got approvals on everything. Management was like, 'No one is forcing us to change it.' [Rockdale] County's OK with it, they say OSHA gave the OK, nobody really raised any red flags, so nothing was really done about it.””

So, there may have been doubts in the minds of management about the adequacy of their fire suppression design, but those doubts would have been eased by the approvals of that design by various regulatory agencies. I doubt, however, that those agencies had any idea about the water reactive nature of TCCA especially if they relied on the BioLab SDS.