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The Behtune Point municipal wastewater treatment plant (WWTP) was modified in 1993 to include an anoxic biological nutrient removal process to reduce discharge of harmful nitrates that promote algae growth in receiving waters. This involved continuous injection of methanol as carbon source for the bacteria which convert nitrates into nitrogen gas. The WWTP was modified again in 1999 to enable operation without continuous methanol feed, but the injection system was retained for sporadic methanol addition. On 11-Jan-06, 3 workers were removing a hurricane-damaged roof shading the partially full 37.9m3 (10,000 US gal) capacity carbon steel above-ground methanol storage tank. Two mechanics were on a man-lift basket cutting the metal roof directly above the tank vent while a crane operator was holding the roof sections as they were being cut. Sparks showering from the cutting torch accidently ignited methanol vapour escaping from the tank vent, creating a fireball on top of the tank. The fire propagated through a defective flame arrester on the tank vent, igniting the methanol /air mixture inside the tank, resulting in an explosion.
Ask yourself and your crew:
- How can something like this happen here (e.g. on our site)?
- What safety measures (i.e. procedures, controls/barriers) do we have in place to mitigate the risk?
- How do we know the risk controls/barriers are working?
- What improvements or changes should we make to the procedures, controls/barriers or the way we work?
Original content courtesy of IChemE Safety Centre
