As you may well know, there are many volcanic gases. These gases help drive the eruption. Initially dissolved in the magma, they expand as the pressure is released, driving the magma out of the vent and causing explosive eruptions. One should also note that anything that boils below the temperature of magma (600-1200°C) should be considered a volcanic gas. A good example is shown here,
where garbage is thrown into a lava lake and subsequently vaporizes; the garbage has turned into volcanic gases.
The most abundant volcanic gas in most cases is water. Water drives volcanism at subduction zones. The wet oceanic crust is pulled into the mantle where it has several effects. First, water is believed to lubricate the process. This may be through a chemical alteration of the rock called serpentinization. Water also decreases the melting point of rock. This, along with the fact that water is lighter than rock, leads to the buoyant plumes of molten rock that feed subduction zone volcanoes. The good news about water is that it is non-toxic. Steam can burn you, cause explosions, and throw hot rocks at you, but it will not poison you. Other volcanic gases are not so nice. We may, or may not, have to worry about them, but we should understand them if there is any chance of exposure.
Before we go any further, it’s important to understand that different substances have different levels of toxicity. For example, both carbon dioxide and hydrogen cyanide are toxic. The current atmospheric concentration of CO2 is close to 400ppm, a level which is absolutely harmless, at least in terms of breathing it. Hydrogen cyanide, in the same concentration, would kill us all in less than an hour. For toxic gases, a good measure of toxicity is the LC50. The definition of the LC50 is the concentration that causes death of half of the exposed critters over a certain period of time. This value is determined experimentally, in a controlled lab setting. For obvious reasons, this is usually tested on rodents, rather than humans. Time is important here, because longer exposures may be deadly with a much lower dose. These numbers are usually geared to occupational exposure, and may not reflect constant exposure volcanic gas over hours or days, but it’s good enough to get some idea of the toxicity. It is important to note that the LOWER the LC50, the more toxic the gas.
Notably, these are the concentrations that kill HALF of the exposed individuals. Death can result from far lower exposure. A good measure for this is the LCLO, which is the lowest concentration in which death has occurred. Again, lower numbers mean greater toxicity. This data is usually far less available, and is generally based on short, high concentration exposures that would occur in an industrial setting. This is an uncontrolled environment, so this data is less reliable than the LC50, and the hazard of longer exposures, such as would occur during a volcanic eruption, are difficult to judge by this metric. Usually, this data tells a similar story to the LC50, but not always. For example, the lowest exposure of hydrogen fluoride known to cause death was 50 ppm for 30 minutes, while hydrogen sulfide has a much higher LCLO, around 600 ppm for the same time frame. The LC50 shows the opposite pattern, with hydrogen sulfide seeming to be much more toxic. Based on this, it seems that sulfur dioxide is more uniformly toxic to all individuals, while some individuals are more susceptible than others to hydrogen fluoride exposure. It’s also important to know that this does not tell the whole story. Hydrogen fluoride, for example, has significant, dangerous effects with long term, low level exposure, and it has ways to get into you other than by breathing.
In addition to these data points, there is another standard of safety that is often encountered. This is the IDLH concentration, which stands for “Immediately dangerous to life or health.” This is the level that is “likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment” according to the NIOSH, or National Institute of Safety and Health, here in the United States. This standard attempts to address additional concerns. A person who is unable to see, unconscious, disoriented, or struggling to breathe is not going to be able to escape a dangerous situation. For example, exposure to concentrations of carbon dioxide far below the lethal level can lead to unconsciousness or disorientation. Hydrogen chloride is also dangerous because it can cause severe tearing up of the eyes, along with severe respiratory irritation significantly below lethal levels, which could lead to incapacitation. While this number is based on scientific information, it is not determined by objective data collected in a controlled lab testing, but rather by regulators looking at data. Therefore, it is far more arbitrary, and may not be as accurate as the other numbers.
|Toxicity data for various volcanic gases:|
|Gas||LC50 (ppm)/exp. time (minutes)||LClo (ppm) / exp. time||IDLH (ppm)||Typical % of volcanic gas^|
|Carbon dioxide||470000A ppm /
|90000H / 5 min||40000 ppm||1-50%|
|Sulfur dioxide||2520 ppm / 60 min||611 / 300 min
1000H / 10 min
|Hydrogen sulfide||444 ppm / 240 min
713 ppm / 60 min
|600H / 30 min
800H / 5 min
|Carbon monoxide||1784 ppm / 240 min||4000H / 30 min||1200 ppm||0-2%|
|Hydrogen fluoride||1276 ppm / 60 min||50H / 30-60 min||30 ppm||<0.3%*|
|Hydrogen chloride||3124 ppm / 60 min||1300H / 30 min||50 ppm||0-1%|
|Data for LC50 and LCLO is for rats unless otherwise noted. IDLH is always for humans.
LC50, LCLO, and IDLH from http://www.cdc.gov/niosh/idlh/intridl4.html
H: Human data
A: Data from https://www.airgas.com/msds/006598.pdf
*: Volcanoes in Iceland typically give much more, though I can’t find reliable data.
^: There are plenty of exceptions.
There is additional information that we need to take into account when judging the danger of volcanic gases. Looking at the table, it would be easy to assume that hydrogen sulfide would be the biggest danger, since it is the most toxic (on the LC50 scale). However, while it is roughly 4 times as toxic as sulfur dioxide, there is typically at least 10 times as much sulfur dioxide. While carbon dioxide is comparably non-toxic, it is often the most abundant toxic volcanic gas. It also is dense, and settles into low-lying areas. Recently, near Mount Nyiragongo, it resulted in the deaths of several children in a low-lying area of a playground. (http://www.pbs.org/wgbh/nova/transcripts/3215_volcanoc.html) It can also concentrate, dissolved in the water at the bottom of a lake, until the water turns over and spills its deadly contents over the landscape. This happened at Lake Nyos in 1986, killing 1700 people. (http://en.wikipedia.org/wiki/Lake_Nyos)
Notably, hydrogen fluoride has the lowest LC50 on the list, but it usually makes up only a tiny fraction of the volcanic gases emitted by a volcano, and so it is rarely a big risk. This is not the case in Iceland, though, where eruptions are known to emit a lot more hydrogen fluoride. I don’t have reliable data for Icelandic eruptions, but Laki is estimated to have emitted 120 million tons of sulfur dioxide, and 8 million tons of hydrogen fluoride. If we assume that only 10% of Laki’s emissions were sulfur dioxide, then that means that hydrogen fluoride emissions were more than double its normal percentage of volcanic gas. If there was more sulfur dioxide, the portion of hydrogen fluoride would have been even higher. That being said, based on toxicity data, sulfur dioxide would have been a serious inhalation hazard long before hydrogen fluoride presented the same danger.
This leads me to the last point on toxicity. There are many factors that affect the concentration of toxic gases. The total amount of emissions, not just the percentage of each gas, is important. A large fissure eruption, like Laki, is going to put out a lot more gases than a small central volcano eruption such as what happened at Eyjafjallajokull. Heavier gases, such as sulfur dioxide and carbon dioxide can settle in low-lying areas, while higher areas may be safer. Wind direction and speed is important. People downwind from a volcanic eruption will face much higher concentrations than those upwind. A fast wind will actually dilute the gas more, and will help keep heavy gases from settling in low areas, but will increase concentrations further downwind.
That is a lot of data, but what does it all mean? Which of the volcanic gases were listed in the table above actually pose a threat? The main risks are from sulfur dioxide, carbon dioxide, and hydrogen fluoride. The rest are dilute enough that they rarely pose a threat. Sulfur dioxide, if present, clearly lets you know it’s there. It is a pungent, choking gas that irritates the nose, throat, and eyes long before it reaches dangerous concentrations. Carbon dioxide should only be a threat in low-lying areas, because of its low toxicity. Its symptoms include shortness of breath, dizziness, and rapid breathing. Hydrogen fluoride should have a strongly irritating, sharp, acidic odor at immediately dangerous levels. However, levels that you can’t detect can be a problem over time. There will be more on this later.
Specific advice for Iceland about the volcanic gas hazard can be found here: http://earthice.hi.is/sites/jardvis.hi.is/files/myndir/Bardarbunga/volcanic_gas_hazard_enska.pdf
OK, volcanic ash is not a gas, but it is an important toxic volcanic emission. In addition to its physical effects, such as weighing down roofs to the point of collapse, smothering crops, clogging car air filters, and contributing to lahars, it also has toxic effects. These are a bit harder to measure and put in a table, though. The first hazard is simply its irritant effect. Ash consists of many sharp-edged rock particles. They can irritate the eyes and respiratory system. As we saw previously, this can pose a danger by hindering one’s ability to escape the situation.
With high levels or prolonged exposure, it can clog up the respiratory system in a condition called silicosis. (http://en.wikipedia.org/wiki/Silicosis) While acute symptoms may reside with time, the silica never comes out of the lungs, so this has the potential to be a permanent condition. Silicosis is not a nice way to die. Silica has an IDLH of 3000mg/m3, a concentration that would cause irreversible illness in 30 minutes. Note that this is a different unit that the PPM’s typically used for gases. Also note that ash can contain toxic materials other than just silica.
Upon further review of the information out there, I found that silicosis is unlikely. While volcanic ash is mostly silica, the most toxic form, (fine, crystalline silica,) is rarely abundant in volcanic ash. It would take years of exposure to crystalline silica rich ash to develop silicosis. Those with preexisting lung diseases, such as asthma, may be more prone to problems, up to and including death. Additionally, there is some evidence that children exposed to ash may be more prone to asthma. However, healthy individuals are unlikely to experience anything more than bronchitis-like symptoms.
The pertinent information on volcanic ash toxicity is presented here: http://www.geo.mtu.edu/~raman/papers2/HorwellBaxterBV.pdf
Many eruptions in Iceland, as well as a few other volcanoes, emit high levels of fluoride. Fluorosilicates in ash can be an even more important source of fluoride than hydrogen fluoride gas. Both fluorosilicates and hydrogen fluoride will adhere to surfaces and foods and dissolve into water. Even at low concentrations that would be harmless in the short term, hydrogen fluoride can be absorbed into the body and slowly cause fluoride toxicity. Fluoride anions bind strongly to calcium, and lock it up, keeping it from being dissolved or utilized by the body. We know about the toxicity of fluoride because there are a few regions of the world where ground water naturally contains toxic levels of fluoride. Although small quantities can harden teeth and bones, too much fluoride starts sucking calcium out of the body, resulting in the opposite effect. This can cause crippling deformities and weakening of the bones. (Here is a link to a picture of individuals suffering from dental and skeletal fluorosis: http://openi.nlm.nih.gov/detailedresult.php?img=3467640_BMJOPEN2012001564f02&req=4) Fluoride toxicity not only affects the bones and teeth, but it can damage the kidneys and interfere with thyroid function. High enough doses can cause vomiting, diarrhea, and cardiac arrhythmia, which sometimes leads to death. Only 1mm of Hekla’s ash, in 1947, was enough to start killing sheep due to fluorosis.
Now, I bet you’re asking, “How can I protect myself from volcanic gases?” Well, first and foremost, I’m only giving advice on the toxicity of volcanic gases and ash, not the other hazards they pose. Ash, in particular, can cause a lot of other problems that I won’t cover here. Second, I’m a chemist, not a volcanologist, so I’m not an expert in this area. If my advice is different from the experts’ advice, listen to the experts. However, I can approach the issue like a chemist would approach toxic chemicals. The first line of defense against toxic gases is knowledge. Knowing the toxicity of a chemical and symptoms of that toxicity is important. Knowing what chemicals you and others may be working with is important, so you know when and how to protect yourself. The same approach applies here. Reading this was a nice start, but you’ll need to know more. Read more on toxic volcanic gases. Listen to the authorities, particularly in developed nations. They should tell you when and where volcanic gases will be most concentrated, and where ash will be falling. They will tell you if you should evacuate. They should tell you if your municipal water supply is unsafe to drink. Watch the weather report to know which way the wind is going to blow. Keep up to date on the status of an eruption.
The second line of defense when dealing with toxic substances is engineering controls. For example, chemists work in a fume hood, which ensures toxic vapors blow away from the chemist. As another example, drums of toxic substances are stored over large, empty containers, which would contain a spill if a drum leaked. You may not think you have any engineering controls working in your favor, but you do! Do you use well water? Or does your city use groundwater? If so, volcanic ash cannot easily contaminate your water supply. Your house, workplace, or car (if the vents are set to recirculate air) can provide protection from volcanic gases. If you are outside, one minute the wind could be blowing healthy air towards you, then seconds later, it could blow hazardous concentrations of gas towards you. Since air only slowly moves into and out of buildings and cars, the composition of air inside will be the average composition of the atmosphere over the last several hours. Staying inside will not protect you for long if you are directly downwind from the eruption, but if the wind is alternately blowing toxic and clean air your way, it can prevent exposure to hazardous concentrations.
The third line of defense is personal protective equipment. You probably know that chemists wear gloves and goggles most of the time in order to protect themselves from accidental exposure to toxic chemicals. We try NOT to depend on these items, though. These devices can fail, and are meant only as a last line of defense. They are no substitute for avoiding exposure to toxic substances. However, they do work, and have saved many chemists from injury or death.
One piece of personal protective equipment that chemists use, which is applicable here, is called a respirator. These come in various types.
The dust masks that you often see (which look similar to the one in the middle) are usually the particulate type, although a few offer limited vapor protection. (Read the package!) These protect you from small particles in the air, and should provide protection from volcanic ash. However, most dust masks will NOT protect you from volcanic gases. The type you need for that is one rated for acids and organic vapors. The most effective respirators fit on the face with a rubber seal, and use cartridges to absorb the gases. A respirator of this type will protect from sulfur dioxide and hydrogen fluoride, but not carbon dioxide. Some of these respirators (right) also provide eye protection. The bad news is that these are expensive, and without being properly fitted, they may leak. They also have a finite capacity to absorb toxic substances; the higher your exposure, the quicker they stop working. Additionally, if the respirator is not rated for particulates, volcanic ash could clog it quickly! If you have one of these or can get one, and you are being exposed to volcanic gases, use it! Of course, the better choice is to avoid volcanic gases, but this is not always possible.
If you don’t have a respirator, or the cartridges run out, and you can’t escape the gases, you’re going to need an alternative plan. Sulfur dioxide and hydrogen fluoride are acidic, and can be neutralized by bases. As shown here, http://www.uhh.hawaii.edu/~nat_haz/volcanoes/vog.php .
Hawaiians have found some ways to deal with sulfur dioxide. Towels dipped in baking soda solution, (a mild base), then draped over a fan can remove sulfur dioxide from the atmosphere. (This should work for HF, too!) Dust masks or bandanas dipped in the solution, then left to dry, and used to cover the face should also be somewhat effective. These options should also filter out most ash. (Note: Baking soda is “sodium bicarbonate” or “sodium hydrogen carbonate”. Do not confuse it with baking powder, which will NOT work. Also, do not confuse it with washing soda, which is “sodium carbonate”, as it can cause skin injury. Most other bases are too toxic to use! ) If you have nothing else, a wet rag over the nose and mouth will absorb some of the acidic gases. This is used by Indonesian sulfur miners, whose life expectancy is only 30 years, but that’s a lot longer than those who try to go up without any protection!
Drinking water safety
Now what about volcanic ash emissions contaminating your drinking water with fluoride? First of all, this is rarely a concern unless you are in Iceland, or you are near a volcano known for fluoride emissions. (Remember, information is your first line of defense!) Of course, many of the readers are from Iceland, so we will talk about it here. First of all, while some people may have suffered from fluorosis during the Laki eruption, there is evidence that fluorosis in humans may not have been widespread. (http://www.nabohome.org/uploads/fsi/FS328-04291_Fluorosis.pdf) If you can’t implement any of the techniques to limit fluoride exposure, you still have a good chance of making it out alive. Indeed, famine due to the death of livestock was the main killer, and with modern transportation, you’ll probably still have access to food.
If you have well water, your water should be safe. The same will be true if you have city water that comes from wells. If you get your water from above ground in any other way, and you are near an erupting, fluoride-emitting volcano, then it would be wise to purify your water. If you have a municipal water supply that comes from above ground, your city might monitor for fluoride, but I wouldn’t count on it. This is not a standard test that local treatment plants do in all locations, especially in countries that don’t fluoridate water. Even if they do monitor it, it is unlikely that they will be able to treat it, as this requires specialized techniques that are expensive and not necessary under normal conditions. Municipal water should still be safe for bathing and washing clothing, as long as they are properly adjusting the pH. Other surface water may not be safe for those purposes.
So, what are your options for removing fluoride from the water? Of course, you could use bottled water, but this will run out early during a crisis. Typical commercial water filters do NOT work. Boiling and freezing do nothing. Even reverse osmosis will not remove fluoride unless the water has a high pH. (This means the water must be basic in order for them to work.) Yet, there are some things you can do. The following link lists several techniques used where ground water naturally contains dangerous levels of fluoride. http://www.samsamwater.com/library/TP40_22_Technologies_for_fluoride_removal.pdf Note that most require lime or other materials, which you may or may not have available. Assuming you don’t, you’ll need an alternative. Distillation is that alternative.
One should be aware that distillation will NOT remove all fluoride if the water that you start with is acidic. Hydrogen fluoride has a boiling point of 19.5°C, so it will readily boil with the water. However, distilled water will be safer than water that has not been distilled. Some fluoride will still be removed, since much of the fluoride emissions from a volcano will be in other forms, such as fluorosilicate minerals. You can decrease the amount of hydrogen fluoride in the distillate by condensing the water above the boiling point of hydrogen fluoride (around room temperature), so don’t use ice or anything cold to condense it. If you want to remove all of the hydrogen fluoride, you need to make the water basic BEFORE you distill it. The safest way to do this is baking soda. A spoonful per gallon should be adequate, as long as you don’t see a bunch of fizzing when you add it. Notice a pattern here? Buy lots of baking soda! There are lots of household uses for it, too, if it turns out you don’t need it. Lime or washing soda should also work to make the solution basic. Lye will work, but it may damage the container and is less safe to handle. Ammonia or bleach will contaminate your distilled water, so don’t use them!
A homemade water still can be made fairly easily. Go ahead and get creative! All kinds of stuff could work. A good video showing a fairly simple design is here:
All you need is a container in which to boil water, which can be sealed except for one opening. That opening should be connected to a long tube, preferably metal, which goes to the container in which you collect your clean water. The end of the tube in the vessel you are heating must be well above the level of the liquid. The collection vessel must NOT be sealed tightly, and the tube must not be clogged, or the steam won’t come over, and you risk an explosion. The longer and thinner the tube, the less water you will lose as steam, but for safety considerations, a wider tube is better. You can also reduce your losses by cooling the end near the collection vessel, (try a damp cloth) and by distilling slowly under the lowest heat that gets you distillate.
There are a few important considerations in operating a still safely. First of all, the pot in which you boil, the tube from that pot, and any steam that comes out of the tube will be dangerously hot! However, burns are not the biggest danger. The biggest danger is if the tube gets clogged. If, for any reason, at any time, the heated vessel is not open to the atmosphere, pressure can build up, causing it to explode. This will result in shards of metal, plus superheated water flying everywhere. In order to avoid this, make sure the part where the water drips out is open to the atmosphere. Do at least a crude filtration before putting water in the pot… no sticks, leaves, or pebbles! Also, do not distill to dryness. It is tempting to try to get all the water out of the pot that you’re heating, but DON’T! Minerals from the water will build up on the inside, and pieces of it may clog the tube. When you finish a batch, be sure to rinse out the pot to get rid of any deposited minerals.
Well, that’s all I have for toxic volcanic gases and toxic ash. Hopefully, you’ve learned a lot. There is a lot more you need to know about safety during volcanic eruptions, most of which deals with the hazards of volcanic ash. However, I think you’ve got toxic gases covered now!