I'm going to jump in here before this thread starts getting out of hand. While muriatic acid at 20 Baume concentration (31.45%) does produce fumes that are noxious the hazard level is quite low to non-existent in an outdoor setting. Despite what has been written in this thread, MA vapors are NOT TOXIC nor are they dangerous in an outdoor pool setting. Let me put some numbers to this -
The odor threshold limit for MA vapors is 5ppm or 7.45 mg per cubic meter of air. This is the threshold at which the average human nose will detect the odors.
The acute inhalation toxicity limit for a 1 hour exposure (rat studies) is 3124 mg/L or 3124 ppm or 4,655 mg/m^3 of air. In other words, you would have to be in an enclosed space for an hour with acid vapor at a concentration of 625 times what you would smell. There is no way you can approach this in an outdoor setting.
The AIHA (American Industrial Hygiene Association) defines the following levels for MA exposure in a workplace environment -
ERPG – 1 (The maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined objectionable odor.): 3 ppm
ERPG – 2 (The maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual’s ability to take protective action.): 20ppm
ERPG – 3 (The maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing life-threatening health effects.): 150 ppm
So, based on the ERPG-2 classification, you would have to be in a confined space with MA vapors at a concentration of 4 times the odor threshold for over an hour before you would become so overwhelmed with the odor that you could not help yourself.
With that said, please let's keep this thread at a reasonable level of discourse. MA certainly has hazards associated with it and should, like any pool chemical, be handled carefully. It should be stored properly (not in a garage) and it should be poured into a pool in the quickest an easiest fashion possible. Pouring MA directly from the bottle into the return water stream at the deepest end of the pool is the safest and most effective way of handling MA. It reduces the amount of vapors produced when compared to using secondary measuring containers and will completely disperse before it ever hits the bottom of the pool. Brushing the pool walls after adding chemicals is always a good idea because it helps to mix the water and distribute them.
Here is the MSDS for MA - http://pooloperationmanagement.com/w...IATIC-ACID.pdf