IN THE MAIL..
This April, the U.S. Chemical Safety and Hazard Investigation Board (CSB) released a report on their investigation of the fire that destroyed the Biolab trichlor facility in Lake Charles, Louisiana, in the wake of Hurricane Laura in August 2020.
CSB reported that when Biolab’s trichlor supply got wet, it burst into flames, ultimately destroying the Biolab manufacturing plant.
Some scientists take serious issue with the CSB’s conclusions.
Service Industry News has received the following article from Thomas Kuechler, Ph.D Inorganic Chemistry, and Jenn Huang, B.S. Chemistry.
Kuechler and Huang argue that trichlor is not combustible when in contact with water and therefore could not have been the sole cause of the fire. Here, they show that trichlor in fact absorbs heat (is endothermic) when in contact with water, and propose alternate possible explanations for the combustion reactions that occurred. The following is their article: On August 27, 2020, Hurricane Laura started fires that destroyed Bio-Lab’s trichloroisocyanuric acid (TCCA) manufacturing plant in Lake Charles, Louisiana. While no one was killed or injured, the plant was down for more than two years, resulting in a national shortage of TCCA for the 2021 and 2022 pool seasons. This incident was investigated by the U.S. Chemical Safety and Hazard Investigation Board (CSB).
On April 24, 2023, the CSB posted their 123-page investigation report on CSB’s website. The June 1 issue of Service Industry News provided an excellent summary of CSB’s findings. However, the CSB’s report contains some significant misconceptions about the reactivity of TCCA, which must be corrected. This article reviews these misconceptions in the light of both laboratory experimental data and decades of operating experience.
CSB concluded that “the cause of the accidental release of chlorine gas from the Bio-Lab Lake Charles facility was rainwater contacting stored trichloroisocyanuric acid, which initiated a chemical reaction, decomposition, and fire”. However, in our combined 42 years of experience with TCCA, all of the experimental data we are aware of and our knowledge of the reactivity of TCCA has consistently shown that TCCA does NOT generate heat when mixed with water and wet TCCA will NOT start a fire.
The heat of mixing and the gas generation rate were measured as specified by NFPA (National Fire Protection Association) 704 Standard System for the Identification of the Hazards of Materials for Emergency Response (2022, Annex F). Equal masses of TCCA and water were mixed at 25°C in a sealed calorimeter, so that both the heat flow and gas release could be measured. The heat of mixing was 0.33 cal/g of total mass (endothermic) and the gas generation rate was steady for 16 hours at 0.41 L of gas/hr/kg of TCCA, some of which was chlorine (Cl2) and nitrogen trichloride (NCl3). No thermal activity was seen after the initial few minutes of mixing.
The experimental results show that TCCAdoes NOT heat up when mixed with water.
CSB’s report noted that TCCA is classified as “Water Reactive Class 1” in the NFPA 400 Hazardous Materials Code, which defines a Water Reactive material as “A material that explodes, violently reacts, produces flammable, toxic, or other hazardous gases; or evolves enough heat to cause self-ignition or ignition of nearby combustibles upon exposure to water or moisture.” Class 1 Water Reactive materials are “Materials whose heat of mixing is at or above 30 cal/g and
less than 100 cal/g.” Class 2 and Class 3 materials have higher heats of mixing. Based on its endothermic heat of mixing, TCCA is not water reactive.
NFPA 704 (Annex F) indicates that materials that generate hazardous gas could be classified as Class 1 even if the heat of mixing is less than 30 cal/g, but does not specify a minimum gas production rate, so it is not clear if TCCA should be classified as Class 1. In contrast, U. S. Department of Transportation (DOT) regulations in 49 CFR 173.124(c) define a Division 4.3 “Dangerous When Wet Material” as “a material that, by contact with water, is liable to become spontaneously flammable or to give off flammable or toxic gas at a rate greater than 1 L per kilogram of the material, per hour”. Since the gas generation rate when mixing TCCA with water at 0.41 L/kg/hr is well below 1 L/kg/hr, TCCA is not classified as a “Dangerous When Wet Material”.
A Class 2 or Class 3 Water Reactive designation tells firefighters to avoid using water when fighting a fire involving these substances. Fires involving TCCA are best controlled with copious amounts of water. The amount of toxic gas generated by the fire is much higher than the amount of toxic gas generated when water is mixed with TCCA. Therefore, extinguishing the fire with water significantly reduces the amount of toxic gases released, and by extension, the hazard. But if TCCA is mislabeled as water reactive, even in Class 1, firefighters may hesitate to use water to control the fire. Mislabeling TCCA as water reactive and letting fires burn results in more hazardous situations.
Both Differential Thermal Calorimetry (DTA) and Accelerating Rate Calorimetry (ARC) results for TCCA show no exothermic (heat producing) reactions up to the melting point. Dry TCCA melts at 250°C (482°F), forming a colorless liquid that slowly decomposes. When the heat is removed, molten TCCA re-solidifies. Thus, the decomposition of TCCA is endothermic (heat absorbing) and is not self-sustaining. The NCl3 generated by the TCCA decomposition reaction is easily dissipated with proper ventilation. If NCl3 does accumulate (confined without proper ventilation), it poses an explosion hazard, not a fire hazard.
Several controlled burn tests sponsored by the Fire Protection Research Foundation have conclusively demonstrated that TCCA should be classified as a Class 1 Oxidizing Solid, which is defined as “An oxidizer that does not moderately increase the burning rate of combustible materials with which it comes into contact or a solid oxidizer classified as Class 1 when tested in accordance with the test protocol set forth in Section G.1.” The burn tests also show that TCCA decomposition is not self-sustaining.
The reactions and fires seen during the Biolab plant xqand warehouse incidents are not at all typical of the behavior of commercial grade TCCA, even when wet. Such behavior has never been seen in more than 50 years of manufacturing TCCA.
Therefore, in contrast to the statementsinCSB’sreport,commercial grades of trichloroisocyanuric acid (TCCA) do NOT react with water to generate heat and should NOT be classified as water reactive. TCCA will NOT decompose when wet to generate a large plume of smoke and hazardous gases, and wet TCCA will NOT start a fire. All of the statements in CSB’s report that the decomposition of wet TCCA is exothermic, generates thick clouds of smoke and toxic gases, and will start a fire, are incorrect and misleading and contradict the experimental data and decades of operating experience.
In contrast, mixtures of TCCA (an acidic material) with alkaline materials, such as sodium carbonate (soda ash) or sodium bicarbonate, can react when the dry mixture is mixed with water. In particular, formulations of TCCA with sodium carbonate are known to be quite reactive with water and decompose differently than TCCA alone. The acidic and basic ingredients react to produce heat and form sodium dichloroisocyanurate dihydrate, which then undergoes a self-sustaining decomposition if heated to its decomposition temperature.
In addition, mixtures of TCCA with sufficient amounts of other materials may not be classified for transportation (under DOT/GHS) as oxidizers.
It can be concluded that whatever reacted with water, decomposed to generate thick clouds of smoke and toxic gases (including chlorine gas), and started the fires at Bio-Lab’s plant was not just a commercial grade of TCCA. If this material contained at least some TCCA, it must have been one or more TCCAbased formulation(s), that is, one or more mixture(s) of TCCA with other ingredients, that caused the fires. Alternatively, the water reactive material could have been an entirely different chemical.
It is not clear from CSB’s report if any TCCA-based formulation(s) was (were) present at the Lake Charles plant because the report simply refers to all of the products that decomposed as TCCA. However, there is publicly available information about some formulations that might have been present.
Some possible formulations include “Chlorinating Granules Plus”, “BioGuard Formulated Chlorinating Granules” or “BioGuard Power Chlor™” (EPA Registration Numbers 67262-29 and 5185-502), which contain 71.8% TCCA and 28.2% other ingredients. It is not clear whether these are exactly the same chemical composition, as only the active ingredients are identified on the labels.
It should be noted that, for transportation purposes, the SDSs indicate these products are not Class 5.1 Oxidizers, unlike TCCA.
CSB’s report showed pictures of bags of product that reacted when they got wet. None of these bags had the oxidizer diamond, UN number, or proper shipping name required for TCCA on the bag. Therefore, it appears that these bags contained materials that were not classified as an oxidizer per DOT regulations.
CSB’s report did not distinguish between TCCAand any possible water reactive materials or formulations. Therefore, the report was unable to properly clarify these differences. These additional details would have been critical information to include so that CSB’s report, which is used to educate the public and the industry about the true chemical hazards, would accurately reflect the actual cause of the incident, instead of inappropriately ascribing the cause of the fires to simply wet TCCA.
Jenn Huang (B.S. Chemistry)
