What Happened
An incident occurred when incompatible chemical wastes were combined in a plastic waste container, leading to overpressurization and a subsequent chemical spray.
The lab’s standard practice was to consolidate various waste streams into a single container labeled "halogenated waste," rather than segregating them by chemical compatibility (e.g., separating aqueous and organic waste). In this instance, the researcher also kept sodium bicarbonate in the waste container to neutralize acid waste.
On the day of the incident, dichloromethane (DCM) was added to the waste container. Given the differences in density and solubility between the DCM and aqueous waste, it is theorized that the liquids formed separate layers within the waste container. This could have led to the incident in two ways: either the layers were suddenly agitated, causing a delayed reaction between the bicarbonate and the acid, or a specific incompatibility occurred between the organic DCM and the acid waste (such as a reaction with nitric acid).
When the researcher moved the container from the fume hood to the waste collection area, the physical agitation disturbed these layers. This allowed the acid to bypass the DCM barrier and react rapidly with the sodium bicarbonate, generating a sudden buildup of carbon dioxide gas. Noticing the bottle was pressurized, the researcher attempted to vent the container by opening the cap. This resulted in the immediate release of pressure, spraying approximately 2 liters of the chemical mixture out of the bottle and onto the researcher’s body and face.
The researcher immediately utilized the emergency shower and eyewash station for decontamination and subsequently reported to the Tang Center for medical evaluation.
What went right?
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The researcher was wearing the appropriate PPE (lab coat, safety glasses, gloves).
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The researcher immediately used the emergency shower and eyewash.
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The researcher reported to the Tang center promptly.
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The lab reached out to EH&S for guidance and help cleaning the spill.
What should be done differently?
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Waste should be properly segregated to avoid incompatible materials reacting. Aqueous and organic waste should be separated.
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Where appropriate, neutralization should be incorporated into procedures.
What corrective actions will be taken?
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The lab will transition from a single “halogenated” waste stream to a segregated system. Separate containers will be established for aqueous acids, non-halogenated organics, and halogenated organics to prevent incompatible mixing.
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The lab will stop the practice of adding neutralizing agents (e.g. sodium bicarbonate) directly to waste accumulation bottles. Any necessary neutralization will be performed separately within a fume hood before the material is added to a waste container, and the neutralization process will be documented in the lab’s written procedures.
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Lab members will discuss chemical compatibility, the hazards of mixing aqueous and organic phases, and the proper procedure for handling pressurized containers in their group meeting.
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Clear signage will be posted at waste collection stations to guide researchers on the correct container for each waste stream.
Lessons Learned
This incident serves as a reminder that chemical compatibility must always be the highest priority when managing waste streams. Consolidating diverse chemical wastes into a single container can result in incompatible materials being stored together. In this case, aqueous acid waste and organic solvent waste should have been segregated.
The use of sodium bicarbonate was intended as a proactive measure to neutralize acidity; however, neutralization or other active chemical processing should not be performed inside a waste accumulation container. When reactive materials are placed together in a waste bottle, differences in liquid density and immiscibility can result in the contents separating into distinct layers. These layers may prevent immediate interaction between reactive materials, allowing a potentially hazardous condition to remain unnoticed until the container is moved or agitated. Subsequent mixing can bring incompatible materials into contact and result in a sudden reaction and release of energy.
Waste accumulation containers should be used only for compatible waste streams and should not be used as reaction or neutralization vessels. Maintaining well-segregated waste streams and evaluating waste based on its specific chemical properties and reactivity is essential for safe chemical waste management.