It's a curious question, and one that those not intimately involved with making calibration gas standards for gas detectors might find surprising. Who in the world smells toxic gases? We all know that carbon monoxide is odorless, but there are a great many gases that are extremely toxic that are described in industry literature as having a variety of smells. Phosphine (PH3), for example, is described as having a "fishy" smell. The BOC Gases MSDS sheet has this Emergency Overview of this fine chemical:
"Irritating to the eyes, skin and mucous membranes. Inhalation may result in pulmonary edema. Phosphine is a central nervous system depressant and toxic to the kidneys. Highly Flammable. This product may spontaneously combust in air."
Lovely. What moron would sniff test phosphine for the industry?
"POTENTIAL HEALTH EFFECT ROUTES OF ENTRY: Inhalation, Skin Contact, Eye Contact, Ingestion. EYE CONTACT: Exposure to liquid or high concentrations of vapor to tissue such as conjunctiva, cornea and lens. SKIN CONTACT: tissue damage, frostbite and serious chemical burns. INHALATION: can vary from none or only mild irritation, to obstruction of breathing severe damage to mucous membranes of the respiratory tract with in pulmonary function may occur. INGESTION: Tissue damage, chemical gas under normal atmospheric conditions and ingestion is unlikely."
And as regards to odor? It says that Ammonia is a: "Colorless gas or compressed liquid with a pungent, suffocating odor."
So why would the question of whether Ammonia has an odor ever come up? The answer is that the parts per million ammonia calibration standards provided by certain manufacturers to calibrate ammonia monitors have proven so unreliable over the years that many people (including myself when I was younger) actually were sniff testing the gas from their cylinders to see if there was any odor at all. Not a good practice, but when Ammonia calibration standards failed to get a response from a detector, technicians tried the obvious- turn the valve slowly and see if they dectected a faint, acrid smell. Upon calling calgas manufacturers and explaining that they couldn't smell anything, they were sometimes told that "Ammonia doesn't have an odor."
The problem has been that manufacturers- even today- have struggled to produce a stable Ammonia standard. For years, certain manufacturers packaged their ammonia mixtures in "Bernzomatic" type propane cylinders (sometimes known as 17 liter cylinders) that were and are entirely unsuitable as a container for ammonia mixtures. What is the sense in having a sophisticated ammonia detection system if it is calibrated with an unstable gas mixture?
And pity the poor fireman or other emergency responder who goes into the field responding to an emergency leak situation with an ammonia detector calibrated with an unreliable ammonia gas mixture. I've spent forty years developing stable gas mixtures and here's why- there's always someone whose life depends on the calibration gas standard being reliable.
Ammonia can Cause Quite the Traffic Back-Up