Fuel to the Fire: Recent reports on gas stoves fail rural Vermont Propane and natural gas are not the same, but have been lumped together in news coverage

 

By Shawn Cunningham
© 2023 Telegraph Publishing LLC

If you’ve read a major newspaper or watched the news on television or listened on the radio, you’ve likely heard that your gas stove is emitting toxic chemicals and other substances that can injure your health — even when the stove is not being used.

But according to the main studies on the topic,  the authors are specifically talking about “natural gas,” which is generally found piped into buildings in metropolitan areas. Here in southern Vermont and in other rural areas, the gas that’s used to cook is propane and the white tanks standing outside most houses here attest to that.  And yet in  dozens of articles, broadcasts and web stories, the generic term “gas stoves” is used lumping propane in with natural gas.

And that can certainly cause confusion for Vermonters, where between 46,000 and 96,000 use propane either as a main heating source or for backup heating, running generators and for cooking.  The U.S. Census figures about 18 percent of Vermonters — or 46,000 homes — heat with propane. And Matt Cota of the The Vermont Fuel Dealers Association says his organization estimates that another 40,000 to 50,000 households use propane as backup heat and/or for cooking.

And that prompts some questions:  Are all flammable gases the same and — if not — what are the risks involved with the propane gas that rural Vermonters cook with compared with the natural gas that is used in Burlington or Boston? And what does that mean for you, your family and your propane stove?

A real problem

According to work done by the Rocky Mountain Institute, the Harvard T.H. Chan School of Public Health, Stanford University and PSE Healthy Energy, natural gas stoves contribute a number of pollutants to the indoor atmosphere. These include:

• Nitrous oxides, which are associated with breathing problems including asthma.
• Carbon monoxide, a colorless, odorless gas that can replace oxygen in the bloodstream and kill.
• Benzene, toluene, xylene, ethylbenzene etc. are toxic volatile organic compounds some of which are considered carcinogenic.
• Particulates including soot, which are lung irritants associated with asthma.
• Formaldehyde, which irritates the skin, throat, lungs and eyes, and can possibly lead to cancer. These substances also occur in consumer products and building materials which can take time to “outgas.”
• Sulfur dioxide, which also irritates the eyes, nose, throat and lungs.

Natural gas itself is a stew of many chemicals pumped out of wells or refined from petroleum. Methane makes up the largest part of natural gas, with the rest being ethane, propane, butane and some “heavier hydrocarbons” like benzene and toluene.  Then there’s varying amounts of carbon dioxide, nitrogen, water vapor, oxygen and even helium. And since the makeup of natural gas is affected by where it’s extracted, substances like sulfur compounds can also be present. In certain areas like west Texas and Alberta, Canada, the amount of sulfur in natural gas can be very high (see below.) To this is added an “odorant” with a smell so foul it alerts people to leaks. When all of that is burned or leaks, the compounds listed above can be released.

But sharp-eyed readers will have noticed that one component of natural gas is propane and therein lies the difference. Propane is part of the natural gas mix, but it can be separated and used as a fuel by itself.

“Propane is produced through a separation technique called fractional distillation,” says Dr. Frankie Wood-Black, Division Chair, Engineering, Physical Science and Process Technology at Northern Oklahoma College*. That’s a process in which propane is removed from the other components like methane.  Propane is thus called a “fraction” of natural gas and is a purer form of fuel that has fewer of the contaminates of natural gas.

But are there still dangers in using propane? Yes. There are dangers in burning any fuel and those begin with not burning it well enough.

Complete combustion vs. incomplete combustion

Before getting into a comparison of propane and natural gas, it would be good to recognize that many of the problems from either gas come from “incomplete combustion” — when the gas doesn’t fully burn. That can be caused by a couple of factors including insufficient oxygen, which can be a result of very tight houses that may not have enough ventilation, and/or burners that need to be adjusted or replaced.

“No matter what the fire source, always worry about incomplete combustion,” says Wood-Black. The biggest health hazards come from incomplete combustion including carbon monoxide – a colorless, odorless gas that can replace oxygen in the bloodstream leading to illness and even death – and soot.

Incomplete combustion of natural gas also allows unburned methane and a number of the contaminate substances in it (like the carcinogen benzene) to escape into the home.

If a propane stove is properly adjusted and there is a sufficient oxygen, the flame will have four byproducts:

• carbon dioxide;
• water;
• heat and
• a small amount of a sulfur compound that comes from the odorant.

With incomplete combustion of propane, add carbon monoxide and soot (carbon), but according to Wood-Black there are far fewer contaminates in propane and in lower concentrations.

An array of harmful chemicals released or created or not

Here are some of the biggest concerns expressed in stories about gas stoves and also some ways how propane differs from the more widespread natural gas.

NOx

One of the biggest worries around burning any kind of fuel – including propane – is the creation of nitrous oxides.

Nitrogen oxides —  NOx — refers to a group of toxic gas compounds made up of nitrogen and oxygen. One of these – nitrogen dioxide – is associated with breathing difficulties including wheezing, coughing, colds, flu, bronchitis and asthma. It can be produced by burning fuels  – like propane and natural gas – in the presence of air which is a mix of nitrogen and oxygen and causing a reaction of that makes the nitrous oxides.

“Air has nitrogen in it and that’s where you are going to get some of those nitrogen oxides. There’s no way around that – no matter what I do, if I’m burning something I’m going to get nitrogen from the air, and form nitrous oxides, an indoor air pollutant I don’t want,” says Wood-Black.

But because there’s often nitrogen in natural gas, cooking with it can form more nitrogen oxides than propane, which at the most only contains trace levels of the element. Cooking with electricity still heats the air and creates nitrogen oxides, but much less than with either propane or natural gas.

Whatever the concentration, NOx is something that gas users need to think about.

Sulfur dioxide

Natural gas wells in a number of places produce gas with heavy concentrations of sulfur in it. This so called “sour gas” – needs to be “sweetened” to “acceptable levels” which means that natural gas from those wells will still contains sulfur.

According to the Wisconsin Department of Health “Sulfur dioxide, SO2, is a colorless gas or liquid with a strong, choking odor….In homes, sulfur dioxide gas can result from tobacco smoke, improperly or inadequately vented gas appliances (such as stoves, ranges, furnaces, or clothes dryers), gas or kerosene heaters, wood or coal stoves, automobile exhaust from attached garages, and malfunctioning chimneys.”

Because the fractionalization process that separates propane from natural gas leaves behind most of the contaminates of natural gas, propane’s sulfur content consists of a trace odorant to alert users if there’s a leak.

Formaldehyde

While propane is seldom mentioned in articles and papers on indoor air pollution, it has been lumped together with natural gas in a few places as creating formaldehyde when they are burned. “Formaldehyde,” according to the Centers for Disease Control, “is a colorless, highly toxic, and flammable gas at room temperature … Exposure to formaldehyde can irritate the skin, throat, lungs, and eyes. Repeated exposure to formaldehyde can possibly lead to cancer.”

California, a nationwide leader in pollution mitigation, in its Indoor Air Pollution from Cooking webpage, developed by the California Air Resources Board, has asserted that both natural gas and propane stoves “release” formaldehyde.

But Wood-Black said she was stumped by that notion. And following an inquiry by The Telegraph, a representative of the Air Resources board said the statement that propane stoves “release” formaldehyde was incorrect and would be removed from its website. As of Tuesday, it remained.

Leaking

One of the most frightening aspects of the coverage is that natural gas stoves are leaking methane and other gases even when they are not being used. Eric Lebel of PSE Healthy Energy was a primary investigator in a study done with Stanford University that looked at the emission of unburned natural gas from stoves in a large number of areas in California.

Lebel told The Telegraph that the researchers looked at natural gas because it’s use is so widespread and it can have such a large effect on climate change. He noted that there isn’t published research into whether propane is less likely to leak than natural gas.

“One thing to know about natural gas is that it’s a greenhouse gas. We were so interested in it because of its climate impact,” said Lebel. “It’s mainly methane which pound for pound is 80 times stronger than CO2 (as a greenhouse gas) over the next 20 years. Propane is not a greenhouse gas if it leaks. Although when you burn it you get CO2, which is a greenhouse gas.”

Lebel also notes that in natural gas, the odorant added often may not be strong enough to alert people to the leak. And once again, there hasn’t been published research on whether  propane, which is heavier than natural gas, has as great a tendency to leak as methane.

But for Wood-Black the difference in the size of methane and propane molecules is a likely factor.

“The size of the molecules contributes to the propensity to leak,” said Wood-Black noting that the smaller, lighter-than-air methane molecule is “harder to keep in the pipe” than the larger, heavier-than-air propane.

Lebel agreed in principle, but said “It makes sense that propane is a larger molecule than methane so it may not be as prone to leaking, but we don’t have answers on propane.”

Lebel and other researchers also found that the leakage of some contaminates in natural gas — especially benzene — were worrying, but the results were more nuanced than has been widely reported.

Note: Eric Lebel clarified his statement below after this story was published. We have left the original published text, followed by Lebel’s clarification in italics.

“We don’t want to say that every stove leaks,” said Lebel. “But in the highest emitting stoves, in areas with the most benzene in the natural gas, concentrations of benzene in smaller, tight kitchens could be like living with a smoker.”

“We did not find that all stoves leak benzene that would result in concentrations comparable to living with a smoker. What we did find, though, was that nearly every stove had detectable levels of emissions while off and nearly every sample of unburned gas that we collected of natural gas contained benzene.”

That’s not every stove or every house, but Lebel is quick to make the point that benzene exposure is cumulative over a lifetime and there is no safe level with its carcinogenic impacts.

CHOICES

With a more nuanced view of gas stove and indoor pollution – what do you do?

Methane – the main component of natural gas – is a greenhouse gas and propane (which does not contain methane)  in its unburned state is not. But both are considered fossil fuels and burning both gases produces CO2, which is a greenhouse gas. Both contribute to climate change although the pipeline delivery system for natural gas offers myriad connections and joints for the powerful greenhouse gas methane to escape into the atmosphere.

So what’s a stove-owner to do?

With the scariest scenarios (methane and benzene leakage as well as the creation of formaldehyde and other NG contaminates)  seemingly off the table for propane users, the questions are how to minimize risk from a current stove and whether to move to an electric or magnetic induction stove or something in between that relies on a gas stove less for cooking.

A couple of factors enter into that. There’s the cost of replacing a gas appliance and how much assistance in the form of credits and rebates are available. In many houses a pretty fair amount of electrical upgrades would be required for electric cooking and those who rent may not have much to say about that.

There’s also the question of whether the rural grid is hardened enough to keep the power on and providing heat and cooking capabilities in the face of more extreme storms and the possibility of bad actors trying to take it down. Much of the United States already cooks with electricity but ironically much of that power is generated by burning natural gas.

There are steps that a propane stove owner can take to reduce the health problems posed by cooking with gas, and there are options for reducing the use of  a gas stove by using a stand alone induction burner or microwave when possible. So, armed with some more detailed knowledge, what to do about the stove with the bright blue flames for now is a matter of personal preference and choice.

Steps to making your propane use safer

So you have decided to keep your propane stove and your propane heater. What should you do to keep those appliances humming along and at the safest level possible?

• Ventilate – get bad stuff – like NOx – out and oxygen in to promote complete combustion. Get a good hood for your propane stove that is vented to the outside. If that isn’t possible, open a window while cooking.
• Propane heaters — hot water and furnaces — should already be vented to the outside along with propane dryers. Make sure they are in good working order.
• Have any gas appliance looked at and tuned up by a certified technician. Soot on the burners or cooking utensils are signs of incomplete combustion and yellow flames point toward contaminates in the propane – including water.
• An air purifier with a HEPA filter is good for removing particulate generated by cooking and wood stoves while other methods like activated charcoal filtering are better for removing volatile organic compounds.

 

* Dr. Wood-Black told The Telegraph that she does not receive any funding from the propane or natural gas industries.