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In this review of BA British Airways Club World London City flight there is one thing I don't understand:

... it was announced that a passenger onboard had a severe nut allergy, so they asked people not to consume nuts on the flight.

I've never seen this in a restaurant or any other setting. I gather it's usually the responsibility of the person suffering from allergy to avoid what they are allergic to (usually with a legally mandated help, like known allergens listed on the menu).

I understand that having a person have an allergic reaction to nuts (which can get very bad) itself is a risk to the whole flight. What I'm missing is how other people eating nuts may endanger the one person with allergy.

The only thing I can think of is perhaps some loose nuts flying into the allergic person's meal (or, more directly, mouth) in a severe turbulence. Is that it? Is it a normal procedure to ask passengers not to eat nuts when there is an allergic person on board?

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    $\begingroup$ As a datapoint for your last question, my last two flights to the US on Delta have both had an announcement that somebody has a severe nut allergy so they won't be serving nuts, though they didn't ask people not to eat nuts they might have brought on board. $\endgroup$ – David Richerby Jan 24 at 11:27
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    $\begingroup$ "The only thing I can think of is perhaps some loose nuts flying into the allergic person's meal (or, more directly, mouth) in a severe turbulence" Allergies can be triggered a lot easier than the far-fetched scenario you describe, I'd recommend you read up on the topic. $\endgroup$ – AEhere supports Monica Jan 24 at 12:06
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    $\begingroup$ @AEhere I just did and ... wow. 5 milligrams put it in a new perspective for me, I had no idea. Things I learn every day. $\endgroup$ – Pavel Jan 24 at 13:49
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    $\begingroup$ Yeah, it's not anything like gluten intolerance or any of a variety of IgG allergies that many of us have and don't know because the effects are felt 12-72h later and it,s hard to link the exposure to the effects. Peanuts are an IgE, and a nasty one, which means BLAMMO. Also, a medical crisis on an intercontinental airplane is a much more serious matter than on land where you can dial 999 or 911. $\endgroup$ – Harper - Reinstate Monica Jan 24 at 19:19
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    $\begingroup$ Most restaurants aren't flying at 35000 feet, and you having an allergic reaction doesn't cost the restaurant tens to hundreds of thousands of dollars like an airplane diversion. $\endgroup$ – TemporalWolf Jan 24 at 21:40
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The problem with a severe peanut allergy is that you don't have to eat a peanut to be affected. With a severe enough allergy, inhaling peanut "dust" can trigger a life-threatening emergency. In a confined space, any number of events could cause an issue: people dumping peanuts into their hands, dusting their hands off, accidentally sneezing while chewing the peanuts, etc.

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  • $\begingroup$ It's a combination of recirculated air and extremely low air-humidity (<5%). This causes airborne allergens to stay in the air indefinitely and circulate through the entire plane. The main problem is once the allergic reaction starts, you can't get away unless you leave the plane, or put on an oxygen mask. $\endgroup$ – Nelson Jan 25 at 2:11
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    $\begingroup$ Peanut allergies can be VERY severe. In this news article, a passenger simply OPENED a package of peanuts 4 rows ahead when everyone was explicitly warned not to at the start of the flight. The child's breathing airway closed but was saved by an epipen. $\endgroup$ – Nelson Jan 25 at 2:16
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    $\begingroup$ Just to add on: This degree of sensitivity is rare, and not everyone who can have fatal reactions to peanuts is this sensitive. I say this as someone who has a life-threatening peanut allergy, but (at least so far) has never reacted simply to particulate in the air. Thus, in case someone reads this and is thinking "huh, that's not how [person they know]'s allergy works" --- reaction types and sensitivities can vary broadly and there's not a lot known yet as to why. Your best source for knowing how sensitive or reactive a person is, is that person themselves. $\endgroup$ – apnorton Jan 25 at 2:46
  • $\begingroup$ @A.Rex Looks like i fell for a myth. Edited and removed that part $\endgroup$ – Kevin Jan 25 at 13:51
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My grandson has a severe peanut allergy. The Doctor has emphasized that this allergy can be fatal if the kid gets a very small dose of peanut, without very prompt treatment!

The common first aid treatment is an injection commonly administered by an EpiPen (or similar) so the EpiPen must be available on very quick notice 24/7. What many people don't realize is that although the EpiPen injection is effective, it is a TEMPORARY solution to the acute problem, and that the patient must be transported to the Emergency Room quickly, even after the EpiPen injection.

That is hard to do at 36,000 feet. It also disrupts everyone's schedule.

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    $\begingroup$ I wish your grandson never needs the EpiPen and that the quality of his life is greatly improved by this precaution! I've acknowledged both the danger and the disruption to everyone in the original question. What I'm interested in is the part the kid gets a very small dose of peanut - can you please elaborate a bit on that part, to get the idea how great the danger is for your grandson when other people are served peanuts? $\endgroup$ – Pavel Jan 24 at 14:31
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    $\begingroup$ @Pavel A cousin of mine has severe peanut allergies. One time she was kissed goodnight on the check, but the spot turned bright red. The person that kissed her did have peanuts at some point that day, and had a small amount of the oils linger. $\endgroup$ – BPugh Jan 24 at 16:24
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    $\begingroup$ +1 for "...the EpiPen injection is effective, it is a TEMPORARY solution to the acute problem..." - while most [citation needed] people probably have heard of EpiPens, I don't know if they realize they are not a remedy for the allergic reaction. So, as I've heard some suggest, the solution is not "Just keep EpiPens on planes and we can eat all the peanuts we want". $\endgroup$ – BruceWayne Jan 24 at 16:53
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    $\begingroup$ I would think that a person would be in more danger from someone who had eaten peanuts in the same seat on a previous flight, than from someone eating peanuts on the same flight 30 rows away. Do airlines do the level of sanitation required to remove trace amounts of peanut oils from cushions and armrests between flights? I think not. $\endgroup$ – Dave Tweed Jan 24 at 17:05
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    $\begingroup$ Just to add to this answer/address the question of peanuts 30 rows away... What happens when the person with the peanut allergy is seated near the lavatory and anyone else has eaten peanuts and also wants to walk to the lav? I know it's not likely, but aviation is 100% about risk mitigation, and I'm sure the risk here of allergen cross contamination in this case is greater than zero. Since the cost of asking people to keep their nuts put away is basically nothing, the question becomes "why wouldn't the airline make such announcements?" $\endgroup$ – nexus_2006 Jan 24 at 18:04
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@Kevin's answer is the reason this precaution is taken. While there doesn't seem to be any evidence that aerosolized peanut oil/dust can cause a severe reaction (source and other source), people think or are afraid that it can. Mind you, if I had a severe enough allergy that I could die quickly without treatment, I might feel the same way because one time that friend of a friend said...

Point is, since aerosolized peanut stuff in a contained recirculated environment puts people on edge and it's the airline's responsibility to care for you, some may take this precaution. This is specific to airline and not other places due to the fact that the sufferer is trapped in a confined space for a long time, in an air recirculated environment without access to proper medical care. Anywhere else, the sufferer can get out and go to a hospital within short order.

Note that some restaurants (5 Guys in the US comes to mind) are so covered in peanuts that they recommend anyone allergic not even enter their store, they just don't want the liability.

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    $\begingroup$ Generally good answer, but the part about recirculated air is a common misconception, not a reality. The entire cabin air is refreshed without outside air roughly every 2-3 minutes and what air is recirculated runs through HEPA filters first. $\endgroup$ – reirab Jan 24 at 21:16
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    $\begingroup$ @reirab Did you mean air is refreshed without outside air or "with"? $\endgroup$ – chux - Reinstate Monica Jan 24 at 23:08
  • $\begingroup$ @chux Yes, I meant "with." Thanks, good catch. Unfortunately, it's too late to edit the comment. $\endgroup$ – reirab Jan 24 at 23:09
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Peanut allergies are nothing to joke about as they are often severe, with very quick onset - the merest hint of a peanut can within a few moment become a life threatening emergency. Once an airplane is in the air it takes a long time to get down even with emergency priority, and airplanes don't have the advanced medical equipment and staff to keep someone in that condition alive.

That circumstance is easily avoidable, which is why it is pretty standard procedure to ask people to make those announcements, and it's why most airlines have switched to pretzels instead of nuts as in-flight snacks. It's not a regulation, it's a risk reduction strategy.

You don't see that happening in a restaurant because people go to a restaurant to eat - a person going to a restaurant can have no expectation they won't come into contact with food, if they have that bad an allergy they would contact the restaurant beforehand and let them know their needs. Also, your typical restaurant is no more than a few minutes from specialized medical help.

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    $\begingroup$ We all understand the severity, and how it is especially inconvenient on a flight, but nobody has answered the root question: How can a person eating a peanut in another row cause an allergic reaction? Does chewing with the mouth open produce peanut fumes or a fine dust that is inhaled? BTW, this question is less specific to aviation than many others that are flagged for being off topic. It is more of a medical question. $\endgroup$ – Michael Hall Jan 24 at 16:38
  • $\begingroup$ @MichaelHall I have never one encountered a restriction like this outside aviation and came across it in an aviation story, which makes it aviation-related for me. I concur about the root question - the nearest we've got is read up on this in comments. $\endgroup$ – Pavel Jan 24 at 16:56
  • $\begingroup$ I think this answer is missing the fact that this question is not about airplanes. $\endgroup$ – Mooing Duck Jan 24 at 17:25
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    $\begingroup$ IMHO, it's about airplanes to the extent that it may be asking why the paranoia about peanuts on planes and not in other public spaces--and several answers/comments have pointed to reasons that are, in fact, fairly specific to planes. $\endgroup$ – StephenS Jan 24 at 18:34
  • $\begingroup$ @StephenS Well, some of them are specific to planes. Others are misconceptions about planes (especially the bit about recirculated air.) At any rate, it seems a perfectly reasonable question to ask here as a common misconception about aviation is still related to aviation. $\endgroup$ – reirab Jan 24 at 21:14
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Surfaces shared by all passengers, and direct contact with other passengers.

The greatest risk is that someone will spread peanut oil from their hands onto a surface the allergy sufferer will likely touch. If the person has a sever enough allergy, then they could have a life-threatening reaction even to trace amounts of oil that has made multiple 'hops' from surface to surface to get where it is now. The oil could travel from the nuts onto someone's hands, then from their hands onto the latch handle of an overhead compartment, and then onto the allergic person's hands.

There are surfaces and objects that are common to all passengers. The lavatory door and appliances are key examples. The allergy sufferer might try to limit their exposure to surfaces like this by wiping them down before touching them, but it's very difficult to do this 100%. You begin to see the problem when you consider the 'multiple hops' could go in an airplane, especially when you consider that one such hop could be a person's clothes. The allergy sufferer might brush against a surface and get the oil on their clothing, then have a reaction ten minutes later when they touch that part of their clothing with their hand. Other passengers might also wipe the peanut oil on their clothing if they forgot to ask for a napkin.

What about the previous flight? Wouldn't these surfaces already be contaminated? It's possible they are contaminated yes, but the primary way peanut oil gets removed from surfaces other than regular cleaning is by many people who don't have the oil on their hands touching the surface. After a person gets peanut oil on a door handle, the next dozen people will each wipe away some of it and dilute it with skin oils when they use the handle, thus eventually making it safe for a peanut-allergic person. This has likely already happened as much as can be hoped for from the previous flight since people don't eat during landing but then go about touching all these surfaces during de-boarding.

The peanut-allergic person's life goal is to not be one of those twelve people who had to touch the peanut oil-ed handle to wipe and dilute the oil back to safe levels. It's a game of managing probabilistic risk VS living life outside of a sealed bubble. With a restaurant, as long as they've picked a place where peanuts aren't on the menu or are rarely on the menu, they can manage this risk without help from others. On a plane, they are crammed in and have to share surfaces with scores of other people. Combine that with peanuts being the in-flight snack that everyone has, and it's a very risky time for them.

Imagine you get on a flight and all the other passengers are humanoid-aliens with green skin. The flight attendant announces that since there are so many of these aliens aboard, they are switching the in-flight snack to their favorite dish: raw poison-ivy plants served as finger-food. The aliens aren't harmed by the poison ivy's oil that causes intense itching rashes and hives on humans, so they are too cavalier, grabbing a poison ivy stalk in their hands and munching down on it, then lazily wiping their hands on the corner of their jacket, then grabbing the seat head rest as they get up to o use the lavatory and touch everything in there too. Do you think you could make it through that flight without getting even a single little spot of poison-ivy rash? Maybe, but it's a harrowing ordeal. And that's just poison ivy. The allergy sufferer won't just get a rash but could die from just a little exposure. Try-reimaging that aliens on a plane scenario but instead of poison ivy they are snacking down on a potent poison like cyanide or ricin.

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    $\begingroup$ Interesting indeed - I see how complex it might get. Incidentally, you mention one interesting thing - problem of (lack of) sanitizing the plane between flights. As I understand it, the crew asked passengers not to eat peanuts on that flight. Off course wedon't know whether BA sanitized the plane or at least the critical surfaces. I might ask BA about that later! Another thing is that people are asked not to eat nuts, which goes further than just not serving them. In that case it is hardly the snack everyone has, but it doesn't make your answer less valid. $\endgroup$ – Pavel Jan 24 at 19:07
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To be completely honest, this is an overreaction. Yes, peanut dust can cause problems, but the problem comes much more from contact with contaminated surfaces (e.g. armrests, tray tables, etc.) from passengers on the previous flight than from dust transported through the air. Cleaning your seat environment with an alcohol wipe or similar before taking your seat is going to make a lot more difference than banning someone 15 rows away from eating peanuts in flight.

Contrary to popular belief, airliner air is actually quite clean - significantly more clean than in most buildings. If you don't have a reaction from someone on the other side of your restaurant eating a peanut, then you're not going to have one from someone sitting on the other end of your plane eating peanuts, either. Airliners actually use quite good air filters and around half of the air is not recirculated at all, but rather dumped out the outflow valve and replaced by outside air (from engine bleed or a scoop.) So, the odds of any significant amount of peanut dust from someone in row 30 reaching an allergic person in row 10 are extremely remote. The airflow is spanwise (from aisle to window,) so only someone within a few rows of you is likely to breathe in any peanut dust you may generate.

According to a study published by the National Institutes of Health,

The vast majority of U.S. airliners use high-efficiency particulate air (HEPA) recirculation filters for cabin air, and these filters are highly effective at collection of solid and liquid particulates.

And according Patrick Smith's Ask the Pilot, due to the fresh outside air mixed in, "there's a total changeover of air every two or three minutes." This is significantly faster than you'll get replacement air in a commercial building, let alone your home.

The only reason that actually makes any real sense for banning everyone on the flight from eating peanuts rather than only the people in nearby rows is that it does not reveal who actually has the allergy, so it's not as embarrassing for them and they don't risk glares or potential harassment from other passengers upset about their lack of peanuts.

As far as whether this is common practice, there are indeed several airlines that do this.

For example, Delta's policy:

If you have a customer that has a peanut allergy, please contact Delta Sales Support or Delta Reservations in advance to have the peanut allergy information noted in the customer’s PNR.

When Delta is notified that a customer has a peanut allergy, we’ll refrain from serving peanuts and peanut products onboard the flight. We'll also advise cabin service to board additional non-peanut snacks, which will allow flight attendants to serve these snack items to everyone onboard.

On the day of travel, customers should notify the airport gate agent of the peanut allergy, if they would like to request to pre-board and cleanse the immediate seating area.

Unfortunately, even with all the above precautions, we still can't guarantee that the flight will be completely peanut-free.

For those unfamiliar with the industry jargon, "PNR" is "Passenger Name Record" and is just the airline industry way of referring to your reservation.

Southwest stopped serving peanuts entirely last year. To honor the occasion, they set up a tongue-in-cheek display case of peanut packages at MCO.

American Airlines does not serve peanuts and allows allergic passengers to board early to wipe down their seat environment.

United Airlines does not serve pre-packaged peanuts on their flights.

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Anecdotal story:

I was on a commercial flight (Delta?) where they announced very clearly that there was a peanut allergy on board, and that peanuts were not permitted for the duration of the flight.

A family near where we sat opened a pack of Nutty Bars. The fragrance of the peanuts - the smell - was immediately obvious. In about 30 seconds, a woman two rows back signaled the flight attendant that she was having health problems related to the peanuts. It was quick because airplanes are small and have limited air volume.

The family heard about the problem and quickly ate the nutty bars. Once they were not exposed to the air, and the woman's issues quickly resolved as the air cleared.

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  • $\begingroup$ "airplanes [] have limited air circulation" citation needed. $\endgroup$ – a CVn Jan 25 at 15:17
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As a person who has anaphalactic reactions to bees (swell up, hard to breath, cardiac arrest possible), it is fast, sudden and very dangerous. Within 15-20 min, even with an adrenaline shot, I can be in severe breathing difficulty. In a cabin atmosphere of 8000ft that would be far more uncomfortable and would trigger a full scale emergency to the nearest sutiable aerodrome. To any bystander on the plane, who has not seen a reaction before, it would be terrifying.

We swell up, turn red and white, get huge hives all over our skin, struggle to breath and then and can go into shock or seem semi conscious due to the extreme tiredness caused after the epipen.

There is probably not much chance a flight could continue enroute to a destination if a person had a full scale anaphalactic reaction. It can be a serious and life threatening medical emergency. Luckily the vast majority of peanut allergies are not this severe. [1]

The reason the airline asks you not to eat them is, the airline has a duty of care to protect the passenger while onboard the aircraft [2], they have a responsibility to not discriminate against that passenger and they have a strong commercial interest to avoid a very expensive and disruptive emergency diversion to an alternate aerodrome.

In addition in most aircraft the fresh to recycled air in a plane is 50-50 percent [3], so a lot of the air and any nut dust could be recirculated from row 1 in first class to row 51 in economy, or someone in row 20 might go to the same toilet to walk past someone in row 37 and expose them via touch, breath or both touching the same surface. Even a cabin crew member may collect the nut packet, then touch a food package that gets passed to the effected person.

It is serious, but yet easily caused and so easily prevented.

[1] https://acaai.org/allergies/types/food-allergies/types-food-allergy/peanut-allergy

[2] https://injury.findlaw.com/torts-and-personal-injuries/in-flight-injuries-on-airplanes.html

[3] https://www.tripsavvy.com/air-quality-during-your-flight-54164

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    $\begingroup$ The air is run through HEPA filters before recirculation, so it's extremely unlikely that peanut dust or oils from another row would travel via the recirculation system. You have much more risk of this in most buildings than in an airplane. $\endgroup$ – reirab Jan 24 at 21:21
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    $\begingroup$ As @reirab says, air circulation isn’t the issue most think it is, but apart from that this is a good answer. Welcome to Aviation.SE! $\endgroup$ – Notts90 Jan 24 at 23:06

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