In every 24-hour HAZMAT course, we teach, we find that students getting their first official dose of “chemical safety” are shocked to find out that most gases at their facility are NOT white in color. Most have seen dozens of videos over their adult lives showing these large white clouds forming during releases of hazardous materials and just figured that what they were seeing was a chemical cloud. So if ammonia (and propane) is NOT a white gas, then why do we see a white fluffy cloud when ammonia/propane is released to the atmosphere? Chlorine gas is not white; it is yellowish-green in color. Why the difference?
Simply put, a clear liquid (like water, ammonia, or propane) will produce a clear gas; however, when this gas comes into contact with moisture in the atmosphere (humidity), a “cloud” is formed, much like a cloud formed by “Mother Nature” in the sky above us. So what we are seeing is the moisture in the air being condensed because the gas being released is having a “cooling” effect on the humidity and condensing it into a nice white cloud. Now, these clouds help us identify the presence of ammonia (or propane), but we MUST NEVER forget that just because we are not standing in the “cloud” does not mean we are at a ZERO EXPOSURE.
To form one of these “white clouds,” we typically have to have a significant amount of the ammonia/propane gas released quickly in order to condense enough water vapor in the atmosphere so that it is visible. Much like the propane response video, I posted last week… just because you are not in the visible cloud does not mean you’re not in a flammable atmosphere of propane (or in an IDLH atmosphere of ammonia!). In fact, a small leak that can produce a flammable and/or IDLH atmosphere will almost always be INVISIBLE in typical atmospheres! Of course, the amount of vapor available in the atmosphere (i.e., humidity levels), whether inside or outside, on any given day will play a major role in how “a cloud” will form from the released gas. Keep in mind, this works with ALL clear liquids, but when we are dealing with something like chlorine, which is an amber-colored liquid, we will get a colored gas cloud.
The takeaway from this brief posting is to understand that just because we do not see a chemical cloud during an uncontrolled release does not mean we are NOT exposed to said chemical and the hazards it presents to workers and the environment. Coupled with the fact that responders will be in Self-Contained Breathing Apparatuses AND that many chemicals have little to no odor, we MUST have the proper capability to detect the presence of a hazardous material (i.e., do NOT rely on sight (or smell) on a HAZMAT scene.