Level 2 · Keeping your head
Carbon monoxide poisoning
No smell, no colour, and it already has all three of you. The only clue is that you all have a headache at the same time.
Printable card
Carbon monoxide: air it, cut it, get out, call
Seven rules, taken from the civil safety first aid recommendations of the French Ministry of the Interior and from the public guidance of the fire and rescue services.
- 1
The sign that should make you think of it
In a closed space, where several people have the same signs of illness with headaches and vomiting, carbon monoxide poisoning has to be suspected. It has no smell and no colour, it is toxic and explosive: nothing announces it.
Recommandations premiers secours, fiches modifiées juin 2018 publiées, fiche “Protection contre le monoxyde de carbone” (PR 02 P 01) (First aid recommendations, sheets revised June 2018, sheet on protection against carbon monoxide) · Direction générale de la sécurité civile et de la gestion des crises (DGSCGC), ministère de l'Intérieur · www.interieur.gouv.fr - 2
Air it thoroughly
Open the windows wide: air the room or rooms involved thoroughly. The guidance also says how you go in: the responder enters the room holding their breath.
Recommandations premiers secours, fiches modifiées juin 2018 publiées, fiche “Protection contre le monoxyde de carbone” (PR 02 P 01) (First aid recommendations, sheets revised June 2018, sheet on protection against carbon monoxide) · Direction générale de la sécurité civile et de la gestion des crises (DGSCGC), ministère de l'Intérieur · www.interieur.gouv.fr - 3
Switch the appliances off
The national guidance asks for it in plain words: stop the appliance from running. The fire and rescue services spell it out: switch off the heating and cooking appliances. While the source is running, the gas keeps coming.
Recommandations premiers secours, fiches modifiées juin 2018 publiées, fiche “Protection contre le monoxyde de carbone” (PR 02 P 01) (First aid recommendations, sheets revised June 2018, sheet on protection against carbon monoxide) · Direction générale de la sécurité civile et de la gestion des crises (DGSCGC), ministère de l'Intérieur · www.interieur.gouv.fr - 4
Get out, and count yourselves
Get the people there out to a ventilated area, preferably outdoors, and gather them together. Gathering together is what lets you know who is missing.
Recommandations premiers secours, fiches modifiées juin 2018 publiées, fiche “Protection contre le monoxyde de carbone” (PR 02 P 01) (First aid recommendations, sheets revised June 2018, sheet on protection against carbon monoxide) · Direction générale de la sécurité civile et de la gestion des crises (DGSCGC), ministère de l'Intérieur · www.interieur.gouv.fr - 5
Call the fire and rescue service
Immediately, and from outside. The guidance names them for a precise reason: among other things they have detectors for this gas. Naming carbon monoxide changes what they send.
Recommandations premiers secours, fiches modifiées juin 2018 publiées, fiche “Protection contre le monoxyde de carbone” (PR 02 P 01) (First aid recommendations, sheets revised June 2018, sheet on protection against carbon monoxide) · Direction générale de la sécurité civile et de la gestion des crises (DGSCGC), ministère de l'Intérieur · www.interieur.gouv.fr - 6
Say who is missing, and where
If one or more people have stayed inside: get out and tell the emergency services immediately, giving how many people are involved and the state each of them is in.
L'intoxication (Poisoning) · Service départemental d'incendie et de secours de Seine-et-Marne (SDIS 77) · www.sdis77.fr - 7
Do not go back in
Do not go back into a poisoned building without a professional's say-so. No human sense can tell you whether the gas has gone: the people arriving have the instrument that measures it.
L'intoxication (Poisoning) · Service départemental d'incendie et de secours de Seine-et-Marne (SDIS 77) · www.sdis77.fr
This card is practice. It replaces neither a certified course nor medical advice. In a real emergency in France: 15 or 112.
The numbers on this site are France's. 112 is the emergency number across the whole European Union. Outside France, know your own country's emergency number.
Sources checked on August 23, 2026 · https://avantlessecours.odersa.org/en/cas/l-intoxication-au-monoxyde-de-carbone · content under the CC BY 4.0 licence.
The written walk-through, scene by scene
This walk-through contains the answers. It is here to read the situation without playing it, to print it, and to keep the page useful without JavaScript.
Scene 1 · Opening
Sunday, 8.40 in the morning, minus two degrees outside. The boiler has been running since last night, the hob is heating water for tea, and every window has been shut for three days.
Your mother has been holding her head since she got up. So have you, for the last hour. Your brother has gone back upstairs to be sick.
Scene 2 · The doubt
On the hallway wall, a grey box nobody ever looks at. Its red light is flashing.
There is nothing to smell. There is nothing to see. There are three of you with the same headache, in a sealed house.
Three people, the same signs, the same room. What do you make of it?
- Right move : It is carbon monoxide until proved otherwise: I open the windows wide right now.
Several people, the same signs, a closed space : The civil safety guidance sets out exactly that reasoning: in a closed space, where several people have the same signs of illness with headaches and vomiting, poisoning by carbon monoxide has to be suspected. And what it asks you to do on the spot is to air the room or rooms thoroughly, entering the room holding your breath. - Mistake : We have all caught the same thing: I send them back to bed and wait for tomorrow.
Nobody got up again : That is precisely the sign that should make you suspect carbon monoxide: several people, in a closed space, with headaches and vomiting in common. An illness does not strike three people at the same hour in the same room. Going back to bed means staying in the gas while asleep. - Not the best choice : I light a scented candle, it smells stuffy in here.
It smells of fig, and nobody feels any better : What you are trying to cover up has no smell at all. The useful move is thirty centimetres from your hand, and it is a window catch.
Scene 3 · Getting out
Both kitchen windows are wide open, the cold air is falling to the floor.
Your mother has sat down on the nearest chair. Your brother is still upstairs.
The windows are open. What next?
- Right move : I switch off the boiler and the hob, and I get everybody outside.
Cut the source, then get everyone out : The fire and rescue services give the sequence in that order: air the room by opening the windows, switch off the heating and cooking appliances, get the people in the room out to a ventilated area, preferably outdoors. The national guidance asks for the same shutdown, in plain words: stop the appliance from running. And it adds that you gather them together: that is how you know who is missing. - Mistake : The windows are enough, we will stay warm indoors: it is minus two out there.
Twenty minutes later, she is on the floor : Airing does not replace getting out. The public guidance asks for both: open the windows, AND get the people in the room out to a ventilated area, preferably outdoors. While the source is running the gas keeps coming, and the cold has never killed anybody in three minutes on a pavement. - Mistake : I go down to the cellar for a closer look at the boiler, it must be that.
The cellar is the most concentrated place in the house : The guidance hands that search to the fire and rescue services, who among other things have detectors for this gas. A bystander spots the source from outside and reports it; he does not go and sniff it in a sealed room. You can name the boiler on the phone without going down to look at it.
Scene 4 · The call
You are on the pavement, in your socks, phone in one hand.
Your mother is sitting on the neighbour's wall. It is cold, and you are finally breathing something clean.
Who do you call, and from where?
- Right move : 18, or 112, from the pavement. And I say I suspect carbon monoxide.
The fire service, and the word “monoxide” : The guidance says to call the fire and rescue services immediately, because among other things they have detectors for this gas. Naming carbon monoxide changes what they send and what they bring. And the call happens outside, not inside. - Mistake : I call from the kitchen, the signal is better by the window.
You are breathing the thing you are describing : The public guidance asks you to get the people in the room out to a ventilated area, preferably outdoors, before anything else. The rescuer is one of them. A call takes several minutes, and those are several more minutes in the room. - Mistake : I call the emergency plumber, he fitted the boiler last year.
Answering machine, and a Sunday rate : The guidance names the fire and rescue services, and for a precise reason: they have detectors for this gas. A heating engineer will come about the cause, later. This morning the question is not the boiler, it is three people who have been poisoned.
Scene 5 · The one still inside
You count: your mother, you. Your brother never came down.
The firefighter is still on the line and asks whether everyone is out.
Somebody is missing, on the first floor. What do you do?
- Right move : I say it on the phone straight away: one person still inside, first floor, in the bathroom.
Get out, tell them, say where : The public guidance is explicit when somebody stays inside: get out of the room and tell the emergency services immediately. What the call has to carry is how many people are involved and the state each of them is in. They arrive equipped to go in where you cannot. - Mistake : I go back up for him on my own, I know this house inside out.
On the landing, your legs stop working : The public guidance says not to go back into a poisoned building without a professional's say-so. You have already been breathing this gas for hours: your reserve is spent, and a second casualty upstairs does not rescue the first. The fire crew have detectors and air on their backs. - Mistake : I wait outside and say nothing, they will find him when they go in.
They are searching the ground floor : What the call has to carry includes how many people are involved and the state each casualty is in: that is what decides the order they search in. A house has several rooms, and the time they spend opening doors is time your brother spends in there.
Scene 6 · Going back in
They have come back out with your brother, and he is talking. One of the crew is writing numbers off a meter.
Your mother is shivering and asks whether you can go in for the coats: the windows have been open for twenty minutes, it must have cleared.
Everybody is cold. What do you do?
- Right move : Nobody goes in until a professional says so. I ask the crew for blankets.
A professional's say-so, not an impression : The public guidance sets the rule with no conditions: do not go back into a poisoned building without a professional's say-so. Carbon monoxide has no smell and no colour: neither your nose nor your eyes can tell you it has gone. The people outside have an instrument that can, and that is why they are here. - Mistake : The air is fresh now, we can go in: you can tell straight away.
There is nothing to smell, and there never was : The fire and rescue services describe it in four words: no smell, no colour, toxic, explosive. What you can feel on the way in is the cold air from the window, not the absence of gas. The rule is not judged by nose: do not go back in without a professional's say-so. - Mistake : I will go in for thirty seconds, just for the coats and the phones.
Thirty seconds is already one breath too many : The rule carries no acceptable duration: do not go back into a poisoned building without a professional's say-so. You have already spent the night in there, and the source has only just been shut off. The coats can wait until the readings are done.
Scene 7 · The crew
They go in with an instrument that shows a number. The number means nothing to anyone but them, and it makes them open every door in the house.
The boiler is condemned with a sticker. All three of you go to hospital, sitting up, talking.
You worked nothing out about this gas: you just noticed that you all had a headache at the same time, and you opened two windows.