State agencies and the U.S. EPA have been slow to release updates and information, or any real assessment of the actual threat to human lives and the environment posed by the fire. This, especially on top of all the anxiety over the devastating effects of Hurricane Helene, has caused reactions here to range from concerned to panic, and a lot of misinformation has been spreading on social media, including Facebook and Reddit.
Let's be clear and look at the facts: Chlorine is a heavier-than-air, greenish-yellow gas with a distinctive, pungent, irritating odor. The odor threshold for chlorine, the concentration at which it can be smelled in the air, is between 0.2 and 0.4 ppm.
For chlorine, the National Institute of Occupational Safety and Health (NIOSH) recommended exposure limit (REL) is that a concentration of 0.5 ppm should not be exceeded during any 15-minute work period. However, NIOSH RELs are just that - recommendations - and are not legally enforceable. The legally enforceable permissible exposure limit (PEL) for chlorine is set by OSHA at 1 ppm, and is not to be exceeded at any time, regardless of duration.
Since the odor threshold (0.2 to 0.4 ppm) is lower than the exposure limits (0.5 to 1 ppm), you'd be able to smell chlorine in the air before it reaches dangerous levels. However, one has to be wary of "olfactory fatigue," the tendency for the mind to ignore odors after some duration of time. Chlorine, though, is also a very strong oxidizing agent, meaning it is a potent irritant to humans eyes, and the lungs and upper respiratory tract, symptoms difficult to ignore.
Acute (short-term) studies have reported tickling of the nose at 0.014 to 0.054 ppm, tickling of the throat at 0.04 to 0.097 ppm, itching of the nose and cough, stinging, or dryness of the nose and throat at 0.06 to 0.3 ppm, burning of the eyes after 15 minutes at 0.35 to 0.72 ppm, and discomfort ranging from eye and respiratory irritation to coughing, shortness of breath, and headaches above 1.0 ppm.
Higher levels of chlorine have resulted in mild mucous membrane irritation at 1 to 3 ppm; chest pain, vomiting, shortness of breath, and coughing at 30 ppm; and toxic pneumonitis and pulmonary edema at 46 to 60 ppm.
The U.S. EPA has set up air-quality monitoring stations around the Biolabs facility. The air samples are not being analyzed by a laboratory (at least those posted so far online) but instead were performed using portable field instruments, specifically hand-held Multi-RAE analyzers, larger Area-RAE equipment, chemical-specific Draeger tubes, and SPM analyzers. There instruments are good for rapid, real-time measurements, but lack the accuracy of laboratory analyses. I'm not implying that they're "inaccurate," but their minimum detection limits (the lowest concentration they can detect) are higher than laboratory analyses, and the accuracy (e.g., +/- 0.00x ppm) isn't as precise as a lab. Still, they're useful, especially for gathering lots of readings in a short time period, and they're used by emergency workers to assess air quality before entering a hazardous environment. If firemen and first responders trust them with their lives, we can take their reported concentrations at face value.
EPA has published the tabulated results of 12 of the monitoring stations online. Analyses are reported for chlorine, hydrogen sulfide, carbon monoxide, and volatile organic compounds, with some stations additionally reporting hydrogen chloride and phosgene. Of the most recent published readings (5:00 pm yesterday), only one of the 12 stations reported chlorine levels at a concentration (1.51 ppm) exceeding the OSHA PEL of 0.5 ppm. The other gasses were all below their respective action levels.
Some people in Atlanta have expressed concern that air monitoring isn't being performed here, as that's the direction the prevailing winds are now going. But the Biolabs facility is some 30 miles away from Atlanta, and if nothing else, dissipation and dispersion will reduce the concentrations from their source area in Conyers. And since the concentrations in Conyers are below the PEL in all but one of 12 stations, and concentrations at that one non-compliant station are below levels with severe health effects, there's no reason to believe that concentrations in Atlanta will be worse, even if they can be smelled.
Here's a guide: if you're healthy and don't suffer from a respiratory illness, it's fine to go outside in Atlanta. You may want to stay indoors if you're asthmatic or suffer from some other respiratory disease. If you can smell chlorine, that means concentrations have risen above 0.2 to 0.4 ppm. There's no reason to panic though, as you're still well below levels harmful to health. If you experience tickling of the throat or itching of the nose, move indoors or at least out of the area you're in (especially low-laying areas where the heavier-than-air gas might accumulate). If you're experiencing pain or discomfort instead of mere tickling or itching, you're approaching the dangerous levels and need to move indoors.
A lot of agencies have been advising that if you're indoor to avoid exposure, you should turn off the air conditioning. That's a boiler-plate recommendation for national advisories. Here in the American South, most AC system are central air systems and circulate indoor air instead of drawing it in from outside like the window-mounted systems used in the North. If you have central air (even with an outdoor compressor) there's no need to turn off the AC.
I'm not dismissing the risk, nor am I justifying the release from Biolabs. I'm as outraged and angry as anyone. However and on the other hand, I don't want people to experience unnecessary stress and anxiety over the issue, or to panic if they can smell chlorine. As a point of comparison, your exposure to toxic gases, especially carcinogenic benzene, is greater every time you fill your tank with gasoline than being outdoors in Atlanta right now.
I don't want people to panic nor do I want to lull them into false complacency, but I do want them to make informed risk decisions.
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