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Discussion about Toxic Residues in Butane-Extracted Hash Oil
collected by Erowid
1.1 Nov 2013 (original 1.0, Jan 2006)
These comments relate to Indra's Honey Oil Technique which uses butane to extract the cannabinoids from cannabis leaf.

In December, 2005, Erowid received a correction request asking us to take down the butane hash oil extraction technique because of concerns over toxic residues that butane would leave in the resulting hash oil. The requester did not provide any contact info and falsely signed the correction request as 'indra', the author of the original article. After doing some searching, it appears that others were also concerned about this issue and the same warning text had been posted to several forums, so we looked into it a little and collected some comments about the issue here.

First, the correction request stated:
"I want to warn all who now advocate using butane to extract hash oil now to stop. First I am a phd on this subject. The marcapitans [sic] and hydrogen sulfide in the gas, and yes it is in all the cans made, is POISON. You will get brain leasions [sic] from them and it is not safe for this reason alone. Reason number two, over 42 folks have died from fire and explosion using this method, it is not safe and having read the FOOL who now offers to teach it to you, is a heartbeat away from the same fate..."
First, it is important to note that the primary danger associated with using butane (or any flammable gas) is fire or explosion. There are several reports of people burning themselves, including at least one death, when smoking while doing a butane extraction or trying to perform a butane extraction indoors. There is no question that this technique can be dangerous if it is improperly used, however the claim being examined is whether there are toxins that make the end product unsafe, even when the extraction is done carefully and without incident.

Second, it is worth noting that the self-described "phd" badly mispelled mercaptans, lied about his identity, provided undocumented claims about the risks and number of deaths, and provided no contact info (unusual when serious health concerns are brought to our attention). These comments can be found on other sites by searching the web for the two misspellings the author uses: 'mercapitans' and 'leasions'.

The toxins the author is concerned about are mercaptans and hydrogen sulfide. Mercaptans and hydrogen sulfide are both added to butane to make it easy to smell. The lighter hydrocarbons such as butane are essentially odorless when pure. Because small amounts of the gaseous fuels can be explosive, strong smelling chemicals are added to them so that they can be detected easily by the nose. These chemicals are added to butane that is used for lighter refills and are approved for this purpose in which (very) small amounts of the butane and odor-chemicals will be inhaled during use.

Based on a cursory look into the subject, the concerns about toxic residue or mercaptans or hydrogen sulfide in retail-available butane are unwarranted. If the resulting oil has a strong sulphurous smell, there may be mercaptan/hydrogen sulfide residue and it should be evaporated further to remove the odor chemicals. The hydrogen sulfide and mercaptans will evaporate off with the butane and will not survive the heat involved with smoking. While this does not mean that using butane for cannabinoid extraction is safe, it strongly suggests the author of the correction notice does not know what they are talking about.

Comments on the Mercaptan and Hydrogen Sulfide Issue
by SA
Hydrogen sulfide is often added to butane and propane gas so that we can smell gas leaks better. It is highly toxic, but not in such tiny quantities. It is also a gas, which means that when you evaporate the butane extraction there will be none left - well, at least no more than what comes off a silver spoon after eating a boiled egg. As long as butane extractions are done outdoors there is no need to worry about H2S. In enclosed spaces it might be a good idea to get some ventialtion happening quickly - not because of the H2S, but rather because of the butane itself.

Mercaptans are sometimes added to butane for the same reason as H2S. They are simply organic sulphur compounds. The second smallest of these is ethanethiol, which is the smelliest gas know to science - hence it is used in this application. It is toxic, but from what I gather less so than H2S. Also, it's intense smell would prevent anyone from using any material that had any residue in it. It boils at about 35 degC and hence leaving your hash oil sitting in an open dish for a little while (few hours) will get these funky compounds to evaporate (if they are even present).

If this guy got a 'phd on this subject' then I wonder what 'this subject' really is. It certainly isn't chemistry cos he can't spell his compounds right (and doesn't even misspell them consistently) and really does not know anything about the physical behaviour and properties of hydrogen sulfide and the thiols (mercaptans). He also does not appear to realise that both thiols and H2S are already in our bodies and hence adding tiny amounts won't be all that detrimental. Anyone who ever smelled their own fart is facing a similar danger :-P

Mercaptans and H2S are both highly flammable, so burning your extracted oil (ie smoking it) will oxidise these to CO2, water and SO2. And yes, the latter isn't good for you, but again, you would ingest more of it in your glass of red wine than from the hash oil.

Introduction to Mercaptans
by the MFL Occupational Health Center, Manitoba, Canada
MFL Occupational Health Center : Mercaptans Overview

What Are Mercaptans

Mercaptans are a group of sulfur-containing organic chemical substances. They smell like rotting cabbage, and are, for the most part, what make pulp mills smell like pulp mills. If mercaptans are in the air, even at low concentrations, they are very noticeable.

Pulp mills are the chief source of mercaptans, although they are also found in production processes of some pesticides, pharmaceuticals and petroleum products. They are also used as an odourizing agent in natural gas. The human body produces them naturally during digestion of beer, garlic and some other foods.

Dangers of Mercaptans

Not very much is known about the dangers of mercaptans, but current research shows that mercaptans are less poisonous than hydrogen sulfide (the gas that smells like rotten eggs).

Levels Allowed in Manitoba

In Manitoba, federal and provincial regulations set .5 parts per million (.5 ppm) as the permissible concentration in the air.

Mercaptans can be smelled at levels very much less than this. They will not affect workers' health until the level is several times higher than 0.5 parts per million.

The concentration level may be measured with a special type of detector tube. This should be done by a qualified technician or occupational hygienist.

How Mercaptans Affect Health

If there is a leakage or a spill of mercaptans, workers may develop headaches and become nauseated and vomit. There may be coughing and irritation of the lungs and inflammation of the eyes, nose and throat. If the concentration is very high, the worker may have difficulty breathing and may turn blue -medically described as "cyanosis". The worker may then lose consciousness and have generalized muscle spasms.

Treatment

The worker should be immediately moved into fresh air. If breathing is difficult, artificial respiration should be given - mouth-to-mouth is best. Oxygen may be necessary.

Recovery

If the exposure has been slight, the coughing and irritation disappear quickly when the worker gets away from the mercaptan concentration. However, if workers are at all worried they should see a physician for confirmation that they have completely recovered. If the reaction has been more serious, or the worker has lost consciousness, he/she should be taken immediately to a hospital.

Any worker who has health problems after exposure to mercaptans should see a doctor.

There has been only one recorded case of a person dying after exposure to mercaptans. He had been exposed to high levels for some time and was found unconscious. However, this poisoning was complicated by the development of other medical conditions.

Long Term Effects

Long-term health effects of mercaptans are not well documented. Because the mercaptans irritate the breathing system, bronchitis is one possible result, but this is not certain at present.

No evidence exists that mercaptans damage other parts of the human body. Liver and kidney damage has been recorded in experimental animals exposed to high mercaptan concentrations.

Cancer

The studies which have been done to date show no evidence that mercaptans cause cancer.

Prevention

Although mercaptans are not the most dangerous substance in the workplace, workers must nevertheless be protected from harmful effects of mercaptan pollution. A prevention program must be carried out cooperatively by workers, supervisors and employers.

Comments on the Mercaptan and Hydrogen Sulfide Issue
CU
First I would note that both mercapitans and hydrogen sulfide are highly detectable by the nose, which is the point of adding them to butane. In my unofficial capacity, I would say that outdoors for personal use is certainly no worse than normal city pollution.

Here is the spec for industrial butane from Cheveron:
Specifications for Fractionation Grade or Normal Butane
AnalysisUnitsMin.Max.TestProcedure
Normal ButaneLiquid Volume%94.0*ASTMD-2163
Propylene, Propane & LighterLiquidVolume%*0.35ASTMD-2163
IsobutaneLiquid Volume%*6.0ASTMD-2163
PentanesLiquid Volume%*1.5ASTMD-2163
Hexane & HeavierLiquid Volume%*0.05ASTMD-2163
Total OlefinsLiquid Volume%*0.35ASTMD-2163
ButadieneLiquid Volume%*0.01ASTMD-2163
TotalOxygenateswt. ppm max*50.0UOP-845
MeOHwt.ppm max*50.0UOP-845
IPA & Heavier Alcoholswt. ppm max*5.0UOP-845
MTBE and other Etherswt. ppm max*2.0UOP-845
Other Oxygenateswt. ppm max*5.0UOP-845
Total Sulfurwt. ppm max*140ASTMD-2784
Free Water Content**NONE***
Fluorides (See Note #1)wt. ppm. max*1UOP-619
Vapor Pressure@100F*N/AASTMD-1267
Volatile Residue: Deg F. @ 95% evaporation*+36ASTMD-1837
CORROSION CopperStrip@100F*No.1ASTMD-1838
Contaminants: The product shall be free of dirt, scale, rust, and all other types of solid contaminants.

Note #1: UOP Method 619 should be used. However, an instrument with a properly calibrated Electrolytic Conductivity (Hallor ELCD) Detector can also be used.

Note #2: The specification defines only a basic purity for this product. This product is to be free of any contamination that migh trender the product unusable for its commonly used applications. Specific contaminates include (but are not limited to) caustics, chlorides, heavy metals, glycol, and inorganic gases.

Commercial, end user butane such as Servisol's butane refills are probably even cleaner:
Servisol Butane 
Refill Manufacturer:Servisol
CFC free
Refined butane gas
Contains no contaminants
Supplied in a 200 ml aerosol can
Mystery Oil in Butane :
However, it is being done through an EMPTY and STERILE borosilicate tube into a STERILE 304SS NSF collection vessel. I released 49 cans of Newport's "Near Zero Impurities" through the empty chamber and then evaporated at 120*f. After 4 hrs at 120*f I observed a relatively thick coating of oil with a 'new-tire' odor. I then video recorded the vessel having a 50th can blasted into it. You can see the 'Mystery Oil' separate as the butane hits the oils that are in the vessel. The oil was then placed under vacuum at -29.9hg at 140*f for 25hrs; the oil did not evaporate (see other posts for further details on the 'purge'). NOTE: This oil was found while loading/recovering closed-loop through filters--ss 50micron and coffee. I did not use filters and ran as an open "BLAST" for video purposes.