If the wrong type of canister is used to store the propane, there can be a reaction between the tank walls and the mercaptan. For example, one form of mercaptan, called tertiary bytylbutyl mercaptan, can react with porous walls of new steel pipe, valves, or tanks. Specifically, it reacts with mill scale and rust, which includes metal oxides, and forms disulfides which are less odorous than mercaptan - thus causing odor fade.
If the wrong type of canister is used to store the propane, there can be a reaction between the tank walls and the mercaptan. For example, one form of mercaptan, called tertiary bytyl mercaptan, can react with porous walls of new steel pipe, valves, or tanks. Specifically, it reacts with mill scale and rust, which includes metal oxides, and forms disulfides which are less odorous than mercaptan - thus causing odor fade.
If the wrong type of canister is used to store the propane, there can be a reaction between the tank walls and the mercaptan. For example, one form of mercaptan, called tertiary butyl mercaptan, can react with porous walls of new steel pipe, valves, or tanks. Specifically, it reacts with mill scale and rust, which includes metal oxides, and forms disulfides which are less odorous than mercaptan - thus causing odor fade.
Propane is heavier than air, and heavier than mercaptan. That means, in a storage tank with a top-releasing valve,any of several kinds of mercaptan would escape beforeused as oderants are mixed at the propane, which, upon releasing pressure, turns from liquid to gasrefinery. Storage tanks are not built Due to transfer propanepressures in gaseous form, only liquid form. Sothe tanks and the physical characteristics (liquefying) of gases at those pressures, you shouldn't see these kindsthe gases mix as a sort of tanks distributing propanea solution.
The normal distribution method of propane from one storage medium to anotherMercaptan is an extremely pungent material, and is detectable at one part per billion. OSHA limits use to transfer the liquid - not gaseous - propane10 parts per million. So This means, if you werevery little amount of mercaptan needs to fill a 1lb canisterbe used for the purpose of propane fromoderant. As a 20lb tankresult, the method requires you to turnslightest amount of contaminants in tanks, valves, or piping; or the 20lb tank upside down and holdslightest mistake in refinery, distribution, or filling, can have a huge impact on its effectiveness.
Mercaptan reacts to many things it above the smaller canistercomes into contact with, allowingand once this happens it no longer has the liquid propaneproperties it was designed to pour downwardbe used for - a means to detect gas leaks. But when
When you consumecan no longer smell the gas, it is said to have "faded". There are many causes for odor fade:
When propane - saygas is consumed, on a BBQ grill - you must use it uprightdepressurizes and becomes a gas. You don't want liquefied Because propane boils and turns to feed your stove. First, because you won't smell the mercaptan if there is a leakgas at very low temperatures, and second-44F, because it's not init remains a proper stategas in most environments. But mercaptan boils and turns to burngas at about 42F, and you end up with incomplete combustionthings get complicated here. This results in a more yellow flame with soot buildup Above 42F, and carbon monoxide as a byproduct.
Now back to mercaptan: it itself is a gas and doesn't liquefy. That means, when you consume propane, you consume both gaseous propane and the mercaptanso, is easily detected. When you pour propane Below 42F, you pour only the propane - not the mercaptan (this isn't entirely true, there are additives to prevent this; but the illustration is valid)a liquid. The large 100 gallon propane tanks are not meant In this state, it has little means to be used for consumptionreach our olfactory senses, only distributionexcept through propane gas itself, which it does so, the tank and valve assembly draws the propane from the bottom of the tank by using the gaseous propane at the top as tiny droplets of the tank to create pressure and push out the liquid propane at the bottom of the tank through valves that eventually come out at the top of the tank. Tanks are built to allow When the transferamount of propane as well as the mercaptanleakage is small, so that your own tank gets its own supply ofthen smelling mercaptan becomes more difficult to do.
So that This is howwhy in the process of propane and mercaptan workcold, now we look to see where thingsit can go wrongbe difficult to detect by smell. The concept
If the wrong type of mercaptan no longer smellablecanister is called "fade". It can happen because of a leak, a reactionused to store the tankpropane, or a reaction to something inside the tank. If there iscan be a leak at the top ofreaction between the tank, the propane walls and the mercaptan will escape, and you'll know it - that's what it's designed to do. But over time, enough gas can escape, leaving only propane left For example, and then you would not smell it anymore. If there is an improper valve assembly that allows the improper distribution of transferone form of propane (which must mix with the mercaptan at the top of the liquefied propane), that could cause not enoughcalled tertiary bytyl mercaptan to mix into the, can react with porous walls of new containersteel pipe, valves, or tanks. Specifically, too muchit reacts with mill scale and rust, which would leave nothing for later transfers. Finallyincludes metal oxides, ifand forms disulfides which are less odorous than mercaptan - thus causing odor fade.
If the tank is improperly built, or an improperwrong method of filling a propane tank is used to store, thenwhere air might be introduced into the tank, the mercaptan can react with the wallsair, weakening the effect of the tankodorant.
What's more What happens here, mercaptan is heavier than airpipes, sotanks, it will tend to settle to the ground once it escapes. Once it gets into the groundand valves can re-oxidize, it stays informing more iron oxide or other rust compounds, which can oxidize the ground -mercaptan and continuescreate disulfides.
The valves and tubes (and tank) need to smellbe treated - even though the propane is not there. Thereforepickled, you could smell theusually by mercaptan, thinking there's a gas leak, when not only is there no gas leak - and if the right tank were used with the wrong tubing or valves, butthat will cause odor fade as the mercaptan is insideadsorbs to the soiltank or flooringvalves. It is for this reason that if you smell "gas"
If the propane contains impurities, you callthere's a qualified person to detectpotential for reactions. Naturally odorized gas usually contains sulfides and fix itmercaptan, and alsotogether creates potential for oxidation and disulfide conversion. For this reason, to remediate the mercaptan residuemost places restrict naturally odorized gas use in consumer use.
You should also be aware that mercaptan is not always usedOutside the tank, sometimes there are other chemicals thatodors are used. Alwaysnot really faded - but some materials can adsorb the mercaptan (adsorb means to stick to, whereas absorb means to mix). If there should beis a foulleak of propane, you'd expect to smell so that it can be detected. But depending onif the chemical used, it may have different reacting properties with propaneleak occurred underground, the tank wallsmercaptan reacts with soil, or impurities inside theleaving odorless propane. Also Worse, some chemicals are added to allow mercaptan to mix with the propane so as to mitigate a leak to allow escape and cause mercaptan fadeit will settle into low areas. My knowledge here Propane is limitednot poisonous, but I think the processit is similar to how they add stabilizers to medicines so thatan asphyxiant. If propane gathers in low areas, you don't have to shake themmight escape explosion hazards, since the medicine becomes suspended in the mediumbut you wont escape oxygen depletion.
https://www.suhresgas.com/help/LP_GAS_ORORIZATION_INFO.html
EDIT: I stand corrected, mercaptan (all kinds) Mercaptan is heavier than propanealso reactive to masonry and fabrics. However, there really are several forms of mercaptan This is one reason, andamong many others, at least three may be used with propane: ethyl should not be stored indoors. Leaks can have mercaptan adsorbed into walls, thiophanefurniture, or amyl mercaptan. The former two require appx 1lb per 10k gallons of LPG; the latter requires about 1.5 lbs per 10k gals of LPGflooring, and fabrics. The question asks only about EM Of course, this leaves a more permanent smell, and anywayover time, that is the one most distributors useyou become "odor fatigued".
Not all propane comes with odorants, although, asOdor fatigue can occur when you constantly smell a distributor, we were required to use only ethyl mercaptan, since our customers were consumerssubstance - either home heating or 20lblike mercaptan (5gal BBQ grill) tanks,- and you get used to it. Being near water treatment plants which give off gases reminiscent of mercaptan, in these conditionsor near landfills which give off similar gasses, odorants are required by law. In the cases where odorants are not used would be in areas where other gas detectors areyou become used, and where odorants would be problematic for its unique applications (thus requiring to the gas detectors)smell and then don't notice it much anymore.
There are studies that suggest that EM "dissipates" after a week "or two". This is nonsenseOdors can be masked, although this is more advertised than I thoughtas well. I have a propane canister I purchased from Walmart last summer, and Working in attempt to edit this question and question that claim, I connected it to my BBQ, opened the valve,environments with strong odors - stronger than mercaptan - can dull your senses and did the smell test: clearly there was a smell, so,you can miss the "two week" claim is debunkedmercaptan.
Also, I have heard that because propane becomes liquid at -44F,People who are older can lose olfactory senses and EM at 42F, that the in-between temp ranges cause problems when released. I leftnot notice a 1lb canister (blow torch) overnight for 11 hours in high of 20F temperature - well below the 42F boiling point for EMproblem. In releasing the gas
People who are sick, I could smell the EM. This seems debunkedsuch as wellthose who have colds, noting other appearances of odor fadetheir olfactory senses are dulled.
I also have several bottles of training propane - trace amounts of propaneFinally, I use them to teach scouts how to screw onto stoves and lamps before letting them use the real deal. Most contained small quantitiesimproper consumption of propane, a few contained nothing detectable can cause odor fade. I used It is not uncommon to use a tapportable BBQ grill with an inflexible pipe connected to push the fill pin and let gas escape. Not much gas escaped as expected; however, there was a noticible amount of gas smell (the EM).
I conclude that EM does not normally fade - by itself1lb canister which is upside down.
When fade DOES happen In this case, it happens as I stated: reaction fromdue to the design of the canister/tank, reaction with impurities inliquid propane pours through the propane; and additionally with reaction with soil, untreated cement, and interior building materialsvalves and furniturepiping and fabric. I mention this for posterity, although probably irrelevant to your questioninto the stove. The fade in these last cases areliquified propane does not because of problems inside the tankmix with air well, but because of adsorption outside the tankand so, due toyou note incomplete combustion by way of yellow flames and soot. (It's a huge waste of propane as well.) If there was a leak from, the tank or valves.
Fade can also occur because mercaptan oxidizes; this shouldn't happen unless air gets intosooty byproduct of the canister, but thatstove burner can happeneasily mask the smell - even burn along with improper fillingit. Additionally In addition, gas can become faded with newthis incomplete combustion also produces a highly toxic gas lines that are not properly treated, called carbon monoxide.
There are cases where odor fade seems to occur Any time you note yellow flames produced from natural gas, but does not: older peoplepropane, smokersbutane, or sick people whose olfactory sensories are compromisedany mixtures therein, odorants are less noticeableyou're sure to wind up with CO. Also, cold conditions can cause people Just one more reason to misskeep the odor as well. Finally, conditions where foul odors are normal can confuse EM release: areas around water processing treatmentsburner outside or landfills are notorious, as anyone who lives in north-eastern New Jersey can attest: on days where rough sewage treatment is occurring, the smell canhave a proper ventilated system. And to be detected for several milessure the canisters are always upright.
EM in all of its forms In fact, some 20lb tanks are not knowndesigned to break down as long as it is mixed with propane properly, and used with proper tank equipmentshut off if they are tilted.
More sources:https://www.suhresgas.com/help/LP_GAS_ORORIZATION_INFO.html
Propane is heavier than air, and heavier than mercaptan. That means, in a storage tank with a top-releasing valve, mercaptan would escape before the propane, which, upon releasing pressure, turns from liquid to gas. Storage tanks are not built to transfer propane in gaseous form, only liquid form. So, you shouldn't see these kinds of tanks distributing propane.
The normal distribution method of propane from one storage medium to another is to transfer the liquid - not gaseous - propane. So, if you were to fill a 1lb canister of propane from a 20lb tank, the method requires you to turn the 20lb tank upside down and hold it above the smaller canister, allowing the liquid propane to pour downward. But when you consume the propane - say, on a BBQ grill - you must use it upright. You don't want liquefied propane to feed your stove. First, because you won't smell the mercaptan if there is a leak, and second, because it's not in a proper state to burn, and you end up with incomplete combustion. This results in a more yellow flame with soot buildup, and carbon monoxide as a byproduct.
Now back to mercaptan: it itself is a gas and doesn't liquefy. That means, when you consume propane, you consume both gaseous propane and the mercaptan. When you pour propane, you pour only the propane - not the mercaptan (this isn't entirely true, there are additives to prevent this; but the illustration is valid). The large 100 gallon propane tanks are not meant to be used for consumption, only distribution, so, the tank and valve assembly draws the propane from the bottom of the tank by using the gaseous propane at the top of the tank to create pressure and push out the liquid propane at the bottom of the tank through valves that eventually come out at the top of the tank. Tanks are built to allow the transfer of propane as well as the mercaptan, so that your own tank gets its own supply of mercaptan.
So that is how the process of propane and mercaptan work, now we look to see where things can go wrong. The concept of mercaptan no longer smellable is called "fade". It can happen because of a leak, a reaction to the tank, or a reaction to something inside the tank. If there is a leak at the top of the tank, the propane and mercaptan will escape, and you'll know it - that's what it's designed to do. But over time, enough gas can escape, leaving only propane left, and then you would not smell it anymore. If there is an improper valve assembly that allows the improper distribution of transfer of propane (which must mix with the mercaptan at the top of the liquefied propane), that could cause not enough mercaptan to mix into the new container, or, too much which would leave nothing for later transfers. Finally, if the tank is improperly built, or an improper tank is used to store, then, the mercaptan can react with the walls of the tank.
What's more, mercaptan is heavier than air, so, it will tend to settle to the ground once it escapes. Once it gets into the ground, it stays in the ground - and continues to smell - even though the propane is not there. Therefore, you could smell the mercaptan, thinking there's a gas leak, when not only is there no gas leak, but the mercaptan is inside the soil or flooring. It is for this reason that if you smell "gas", you call a qualified person to detect and fix it, and also, to remediate the mercaptan residue.
You should also be aware that mercaptan is not always used, sometimes there are other chemicals that are used. Always, there should be a foul smell so that it can be detected. But depending on the chemical used, it may have different reacting properties with propane, the tank walls, or impurities inside the propane. Also, some chemicals are added to allow mercaptan to mix with the propane so as to mitigate a leak to allow escape and cause mercaptan fade. My knowledge here is limited, but I think the process is similar to how they add stabilizers to medicines so that you don't have to shake them, since the medicine becomes suspended in the medium.
https://www.suhresgas.com/help/LP_GAS_ORORIZATION_INFO.html
EDIT: I stand corrected, mercaptan (all kinds) is heavier than propane. However, there really are several forms of mercaptan, and, at least three may be used with propane: ethyl mercaptan, thiophane, or amyl mercaptan. The former two require appx 1lb per 10k gallons of LPG; the latter requires about 1.5 lbs per 10k gals of LPG. The question asks only about EM, and anyway, that is the one most distributors use.
Not all propane comes with odorants, although, as a distributor, we were required to use only ethyl mercaptan, since our customers were consumers - either home heating or 20lb (5gal BBQ grill) tanks, and, in these conditions, odorants are required by law. In the cases where odorants are not used would be in areas where other gas detectors are used, and where odorants would be problematic for its unique applications (thus requiring the gas detectors).
There are studies that suggest that EM "dissipates" after a week "or two". This is nonsense, although this is more advertised than I thought. I have a propane canister I purchased from Walmart last summer, and in attempt to edit this question and question that claim, I connected it to my BBQ, opened the valve, and did the smell test: clearly there was a smell, so, the "two week" claim is debunked.
Also, I have heard that because propane becomes liquid at -44F, and EM at 42F, that the in-between temp ranges cause problems when released. I left a 1lb canister (blow torch) overnight for 11 hours in high of 20F temperature - well below the 42F boiling point for EM. In releasing the gas, I could smell the EM. This seems debunked as well, noting other appearances of odor fade.
I also have several bottles of training propane - trace amounts of propane, I use them to teach scouts how to screw onto stoves and lamps before letting them use the real deal. Most contained small quantities of propane, a few contained nothing detectable. I used a tap to push the fill pin and let gas escape. Not much gas escaped as expected; however, there was a noticible amount of gas smell (the EM).
I conclude that EM does not normally fade - by itself.
When fade DOES happen, it happens as I stated: reaction from the canister/tank, reaction with impurities in the propane; and additionally with reaction with soil, untreated cement, and interior building materials and furniture and fabric. I mention this for posterity, although probably irrelevant to your question. The fade in these last cases are not because of problems inside the tank, but because of adsorption outside the tank, due to a leak from the tank or valves.
Fade can also occur because mercaptan oxidizes; this shouldn't happen unless air gets into the canister, but that can happen with improper filling. Additionally, gas can become faded with new gas lines that are not properly treated.
There are cases where odor fade seems to occur, but does not: older people, smokers, or sick people whose olfactory sensories are compromised, odorants are less noticeable. Also, cold conditions can cause people to miss the odor as well. Finally, conditions where foul odors are normal can confuse EM release: areas around water processing treatments or landfills are notorious, as anyone who lives in north-eastern New Jersey can attest: on days where rough sewage treatment is occurring, the smell can be detected for several miles.
EM in all of its forms are not known to break down as long as it is mixed with propane properly, and used with proper tank equipment.
More sources:
Propane and any of several kinds of mercaptan used as oderants are mixed at the refinery. Due to pressures in the tanks and the physical characteristics (liquefying) of gases at those pressures, the gases mix as a sort of a solution.
Mercaptan is an extremely pungent material, and is detectable at one part per billion. OSHA limits use to 10 parts per million. This means, very little amount of mercaptan needs to be used for the purpose of oderant. As a result, the slightest amount of contaminants in tanks, valves, or piping; or the slightest mistake in refinery, distribution, or filling, can have a huge impact on its effectiveness.
Mercaptan reacts to many things it comes into contact with, and once this happens it no longer has the properties it was designed to be used for - a means to detect gas leaks.
When you can no longer smell the gas, it is said to have "faded". There are many causes for odor fade:
When propane gas is consumed, it depressurizes and becomes a gas. Because propane boils and turns to a gas at very low temperatures, -44F, it remains a gas in most environments. But mercaptan boils and turns to gas at about 42F, and things get complicated here. Above 42F, mercaptan is a gas, and so, is easily detected. Below 42F, mercaptan is a liquid. In this state, it has little means to reach our olfactory senses, except through propane gas itself, which it does so as tiny droplets of liquid. When the amount of propane leakage is small, then smelling mercaptan becomes more difficult to do. This is why in the cold, it can be difficult to detect by smell.
If the wrong type of canister is used to store the propane, there can be a reaction between the tank walls and the mercaptan. For example, one form of mercaptan, called tertiary bytyl mercaptan, can react with porous walls of new steel pipe, valves, or tanks. Specifically, it reacts with mill scale and rust, which includes metal oxides, and forms disulfides which are less odorous than mercaptan - thus causing odor fade.
If the wrong method of filling a propane tank is used, where air might be introduced into the tank, the mercaptan can react with the air, weakening the effect of the odorant. What happens here, is pipes, tanks, and valves can re-oxidize, forming more iron oxide or other rust compounds, which can oxidize the mercaptan and create disulfides.
The valves and tubes (and tank) need to be treated - pickled, usually by mercaptan - and if the right tank were used with the wrong tubing or valves, that will cause odor fade as the mercaptan adsorbs to the tank or valves.
If the propane contains impurities, there's a potential for reactions. Naturally odorized gas usually contains sulfides and mercaptan, and together creates potential for oxidation and disulfide conversion. For this reason, most places restrict naturally odorized gas use in consumer use.
Outside the tank, odors are not really faded - but some materials can adsorb the mercaptan (adsorb means to stick to, whereas absorb means to mix). If there is a leak of propane, you'd expect to smell it. But if the leak occurred underground, the mercaptan reacts with soil, leaving odorless propane. Worse, it will settle into low areas. Propane is not poisonous, but it is an asphyxiant. If propane gathers in low areas, you might escape explosion hazards, but you wont escape oxygen depletion.
Mercaptan is also reactive to masonry and fabrics. This is one reason, among many others, propane should not be stored indoors. Leaks can have mercaptan adsorbed into walls, furniture, flooring, and fabrics. Of course, this leaves a more permanent smell, and over time, you become "odor fatigued".
Odor fatigue can occur when you constantly smell a substance - like mercaptan - and you get used to it. Being near water treatment plants which give off gases reminiscent of mercaptan, or near landfills which give off similar gasses, you become used to the smell and then don't notice it much anymore.
Odors can be masked, as well. Working in environments with strong odors - stronger than mercaptan - can dull your senses and you can miss the mercaptan.
People who are older can lose olfactory senses and not notice a problem.
People who are sick, such as those who have colds, their olfactory senses are dulled.
Finally, improper consumption of propane can cause odor fade. It is not uncommon to use a portable BBQ grill with an inflexible pipe connected to a 1lb canister which is upside down. In this case, due to the design of the canister, liquid propane pours through the valves and piping and into the stove. The liquified propane does not mix with air well, and so, you note incomplete combustion by way of yellow flames and soot. (It's a huge waste of propane as well.) If there was a leak, the sooty byproduct of the stove burner can easily mask the smell - even burn along with it. In addition, this incomplete combustion also produces a highly toxic gas, called carbon monoxide. Any time you note yellow flames produced from natural gas, propane, butane, or any mixtures therein, you're sure to wind up with CO. Just one more reason to keep the burner outside or have a proper ventilated system. And to be sure the canisters are always upright. In fact, some 20lb tanks are designed to shut off if they are tilted.
https://www.suhresgas.com/help/LP_GAS_ORORIZATION_INFO.html
EDIT: I stand corrected, mercaptan (all kinds) is heavier than propane. However, there really are several forms of mercaptan, and, at least three may be used with propane: ethyl mercaptan, thiophane, or amyl mercaptan. The former two require appx 1lb per 10k gallons of LPG; the latter requires about 1.5 lbs per 10k gals of LPG. The question asks only about EM, and anyway, that is the one most distributors use.
Not all propane comes with odorants, although, as a distributor, we were required to use only ethyl mercaptan, since our customers were consumers - either home heating or 20lb (5gal BBQ grill) tanks, and, in these conditions, odorants are required by law. In the cases where odorants are not used would be in areas where other gas detectors are used, and where odorants would be problematic for its unique applications (thus requiring the gas detectors).
There are studies that suggest that EM "dissipates" after a week "or two". This is nonsense, although this is more advertised than I thought. I have a propane canister I purchased from Walmart last summer, and in attempt to edit this question and question that claim, I connected it to my BBQ, opened the valve, and did the smell test: clearly there was a smell, so, the "two week" claim is debunked.
Also, I have heard that because propane becomes liquid at -44F, and EM at 42F, that the in-between temp ranges cause problems when released. I left a 1lb canister (blow torch) overnight for 11 hours in high of 20F temperature - well below the 42F boiling point for EM. In releasing the gas, I could smell the EM. This seems debunked as well, noting other appearances of odor fade.
I also have several bottles of training propane - trace amounts of propane, I use them to teach scouts how to screw onto stoves and lamps before letting them use the real deal. Most contained small quantities of propane, a few contained nothing detectable. I used a tap to push the fill pin and let gas escape. Not much gas escaped as expected; however, there was a noticible amount of gas smell (the EM).
I conclude that EM does not normally fade - by itself.
When fade DOES happen, it happens as I stated: reaction from the canister/tank, reaction with impurities in the propane; and additionally with reaction with soil, untreated cement, and interior building materials and furniture and fabric. I mention this for posterity, although probably irrelevant to your question. The fade in these last cases are not because of problems inside the tank, but because of adsorption outside the tank, due to a leak from the tank or valves.
Fade can also occur because mercaptan oxidizes; this shouldn't happen unless air gets into the canister, but that can happen with improper filling. Additionally, gas can become faded with new gas lines that are not properly treated.
There are cases where odor fade seems to occur, but does not: older people, smokers, or sick people whose olfactory sensories are compromised, odorants are less noticeable. Also, cold conditions can cause people to miss the odor as well. Finally, conditions where foul odors are normal can confuse EM release: areas around water processing treatments or landfills are notorious, as anyone who lives in north-eastern New Jersey can attest: on days where rough sewage treatment is occurring, the smell can be detected for several miles.
EM in all of its forms are not known to break down as long as it is mixed with propane properly, and used with proper tank equipment.
More sources:
EDIT: I stand corrected, mercaptan (all kinds) is heavier than propane. However, there really are several forms of mercaptan, and, at least three may be used with propane: ethyl mercaptan, thiophane, or amyl mercaptan. The former two require appx 1lb per 10k gallons of LPG; the latter requires about 1.5 lbs per 10k gals of LPG. The question asks only about EM, and anyway, that is the one most distributors use.
Not all propane comes with odorants, although, as a distributor, we were required to use only ethyl mercaptan, since our customers were consumers - either home heating or 20lb (5gal BBQ grill) tanks, and, in these conditions, odorants are required by law. In the cases where odorants are not used would be in areas where other gas detectors are used, and where odorants would be problematic for its unique applications (thus requiring the gas detectors).
There are studies that suggest that EM "dissipates" after a week "or two". This is nonsense, although this is more advertised than I thought. I have a propane canister I purchased from Walmart last summer, and in attempt to edit this question and question that claim, I connected it to my BBQ, opened the valve, and did the smell test: clearly there was a smell, so, the "two week" claim is debunked.
Also, I have heard that because propane becomes liquid at -44F, and EM at 42F, that the in-between temp ranges cause problems when released. I left a 1lb canister (blow torch) overnight for 11 hours in high of 20F temperature - well below the 42F boiling point for EM. In releasing the gas, I could smell the EM. This seems debunked as well, noting other appearances of odor fade.
I also have several bottles of training propane - trace amounts of propane, I use them to teach scouts how to screw onto stoves and lamps before letting them use the real deal. Most contained small quantities of propane, a few contained nothing detectable. I used a tap to push the fill pin and let gas escape. Not much gas escaped as expected; however, there was a noticible amount of gas smell (the EM).
I conclude that EM does not normally fade - by itself.
When fade DOES happen, it happens as I stated: reaction from the canister/tank, reaction with impurities in the propane; and additionally with reaction with soil, untreated cement, and interior building materials and furniture and fabric. I mention this for posterity, although probably irrelevant to your question. The fade in these last cases are not because of problems inside the tank, but because of adsorption outside the tank, due to a leak from the tank or valves.
Fade can also occur because mercaptan oxidizes; this shouldn't happen unless air gets into the canister, but that can happen with improper filling. Additionally, gas can become faded with new gas lines that are not properly treated.
There are cases where odor fade seems to occur, but does not: older people, smokers, or sick people whose olfactory sensories are compromised, odorants are less noticeable. Also, cold conditions can cause people to miss the odor as well. Finally, conditions where foul odors are normal can confuse EM release: areas around water processing treatments or landfills are notorious, as anyone who lives in north-eastern New Jersey can attest: on days where rough sewage treatment is occurring, the smell can be detected for several miles.
EM in all of its forms are not known to break down as long as it is mixed with propane properly, and used with proper tank equipment.
More sources: