32 m³ is about 4m × 4m × 2m. A small car is nearer 3 m³.
Assumes someone is vaping throughout and the other person stays put. The slider stops at four hours because beyond that a single-session model stops being the right tool — use the cumulative section below instead, which is what a whole day repeated actually looks like.
Moderate — about 1 min between puffs
This is the question the old "low / heavy" labels never answered. Six puffs an hour is one every ten minutes. Two hundred and forty is one every fifteen seconds, which is close to continuous and is a ceiling rather than a habit.
Separate from how often, and it matters more for the carcinogens than for the nicotine. Carbonyl production climbs steeply with coil temperature.
This is the one variable anybody can change on the spot, and it moves the bystander numbers more than anything else here.
Roughly 240 puffs over that period.
| Component | Person vaping retained dose |
In the room air average concentration |
Bystander retained dose |
|---|
Two comparisons, and they say different things
Nicotine. What is taken in works out at about 1.5 cigarettes' worth for the person vaping, and 0.02 for the bystander.
Carcinogens. On the same session, as a fraction of what one cigarette delivers — and these differ by more than a hundredfold between them, which is the point:
| Compound | Cigarettes' worth, by mass |
|---|
Formaldehyde is the one that comes closest, and it is not a coincidence. It is produced by heating the carrier liquid, so it scales with coil temperature and puff count in a way the others do not. Acetaldehyde and acrolein come mostly from burning tobacco, which is why they stay one or two orders of magnitude lower.
Both halves, or neither. Nicotine is what makes both products addictive and it is close to irrelevant to cancer. Formaldehyde, acetaldehyde, acrolein and the coil metals are the part that bears on cancer and on the blood vessels, and they are real — a vape is not a water vapour machine. They are also, on the published yields, a small fraction of what the same person would inhale from cigarettes; modelling work puts the cancer potency of most e-cigarette emissions below 1% of tobacco smoke, with exceptions. That is not a contradiction of the table above, and the difference is worth understanding: mass is not potency. A microgram of formaldehyde and a microgram of a tobacco-specific nitrosamine are not equivalent risks, and the compounds that carry most of tobacco smoke's cancer potency — the nitrosamines and polycyclic aromatic hydrocarbons produced by combustion — are largely absent here rather than merely reduced. So vape aerosol can approach a cigarette on one compound by weight while remaining far below it on total carcinogenic potency. Both statements are true and the page gives both. Quoting the carcinogens without that denominator would push a smoker back toward cigarettes, which is the most harmful thing this page could do. Quoting the denominator without the carcinogens would tell a never-smoker there is nothing here, which is also untrue.
The same session, repeated
One evening in a room is not the exposure that matters. The exposure that matters is the same evening happening again tomorrow, and for years. This takes whatever you set above and multiplies it by the days — which is arithmetic, and is as far as anyone can honestly go.
What the cumulative figures are good for is the thing the single-session view hides. For carcinogens without a threshold, the total inhaled over time is the best available proxy for risk — the same logic that makes lifetime apoB exposure matter more than any one reading in the cardiovascular chapters. A dose that looks negligible for one evening is the same dose seven thousand times over by twenty years, and that is a different quantity even though nothing about the evening changed.
Reading the bystander row, which is the one that should change behaviour
- A bystander gets no benefit whatsoever. The person vaping is, in most cases, doing it instead of smoking — a trade with a large upside. Nobody else in the room is making that trade. Their exposure is pure cost.
- And for them the nicotine is the least of it. Nicotine is nearly all retained by the person vaping — about 97% — so very little reaches the room. The particles, the carrier aerosol and the carbonyls are exhaled in far greater proportion. So the bystander's exposure profile is, relatively speaking, more weighted toward the components that are not the addictive one.
- Children get more of it than the table says. The bystander column uses an adult breathing rate. A child breathes less air in absolute terms but substantially more per kilogram of body weight, and has a longer remaining lifetime for a cumulative exposure to act over. Both push the same way.
- Ventilation is the whole game. Change nothing else and move the ventilation control from sealed to well ventilated. The bystander numbers fall by roughly an order of magnitude, and that is a window, not a policy.
What the model does
- The person vaping — puffs per minute × minutes × the amount per puff, then multiplied by the fraction the lungs actually retain (97% for nicotine, around half for the aerosol mass).
- The room — whatever is not retained gets exhaled. That accumulates in a single well-mixed box against ventilation losses, averaged across the session rather than taken at the peak.
- The bystander — that average concentration × an adult breathing rate of 0.72 m³/hr × the time in the room.
Two things the model cannot do. It assumes the air is perfectly mixed, when in reality the person sitting next to the vaper gets considerably more than the average and the person by the window gets less. And fine particles from vaping evaporate quickly rather than persisting like smoke particles, so the PM2.5 figure likely overstates what lingers while understating what you get in the first minute near the source.
Where indoor vaping is not covered by law
UK smoke-free legislation covers combustible tobacco. It does not automatically cover vaping, so whether someone may vape in a workplace, a pub, a car or a home is a matter of the property owner's policy rather than the law. The people most exposed are therefore the ones with least say in the matter — children in cars and homes.
Set the room size to 3 m³ and the ventilation to sealed to see what a car looks like.