Your are almost correct.😊 If the actual half-life (50%) was 1.5 days, then 25% would be 2.25 days. So the high volatilization of vinyl chloride and it’s short half life allows for it to dissipate in roughly 2 days. Could be slightly more but we are splitting hairs at that point.

Half life is not just used for radioactivity. Half life of a chemical reaction is the time it takes to reach 50% of its original concentration. That being said, in the environmental and toxicology space, they utilize that term to denote the timeframe where the chemical is of less concern to be in the atmosphere. Vinyl chloride’s volatilization takes 1 to 2 days in air. “If vinyl chloride is released to the atmosphere, it can be expected to exist mainly in the vapor-phase in the ambient atmosphere and to degrade rapidly in air by gas-phase reaction with photochemically produced hydroxyl radicals with an estimated half-life of 1.5 days.” Direct quote from this technical fact sheet: https://semspub.epa.gov/work/05/437069.pdf

You’re welcome!

I am a geologist and work in the environmental remediation space. I responded to a similar post earlier today under the NoVA page.

There is a lot of misinformation out there on the internet in regards to this emergency response event. There is no way this event could impact us in the DMV. The half-life of vinyl chloride is 1-2 days in air (meaning it ceases to exist after that time). If you refer to a vinyl chloride Safety Data Sheet, you will determine that it is a liquid under pressure, but immediately becomes explosive when mixed with air. That is why the emergency response entity determined that they had to “burn” it off. There really was no other way to deal with the vinyl chloride once it was exposed to air. The burn off is scary and unfortunate, but within 1-2 days it is no longer present in the atmosphere. The long term investigation will more so be related with groundwater. That is something I cannot speak to because I have not seen the data and delineation of contamination can take a while to determine. There was an immediate die off of aquatic animals since vinyl chloride is highly toxic and it hit surface water bodies. Aquatic life pull oxygen from water to breath. Vinyl chloride is more soluble in water.