your ultimate smoke detectors GUIDE
We are happy that you come here. It means
You are aware of fire risks at home.
You care for your family and want to do something to ensure their safety.
You know smoke detector / alarm is an integral part of fire safety at home.
You are actively searching/learning on what to look out for in the purchase of a smoke detector.
This Q&A guide will answer all of the questions you have regarding smoke detectors / alarms. It may also have questions that have not come across your mind. In the event of a question that you cannot find, we welcome you to email us the question through email@example.com. We will help to address that question and update into this guide, which eventually will benefit many others.
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Let’s get started!
Is there a difference between a smoke alarm and a smoke detector?
In today’s context, the terms “smoke alarm” and “smoke detector” are used interchangeably by most, even mainstream media, eg Straits Times. However there is a subtle difference between these 2 terms.
A smoke alarm is an all-in-one, self-contained device, with a detector, which senses the products of combustion (smoke) and sounds an audible, and sometimes visual warning or alarm. This is used mainly in residential settings.
A smoke detector senses smoke only and must be connected to a fire alarm system control panel to activate an audible, and sometimes visual warning or alarm. It is NOT a stand-alone unit. Smoke detectors are a detection device only – not an alarm. This is used mostly in commercial / industrial settings where there are multiple, potentially hundreds of, smoke detectors all linked to a central fire alarm system control panel monitored from within the building’s fire security office.
So the key difference between these 2 is that the smoke alarm is a stand-alone unit that detects smoke and sounds off the alarm while the smoke detector only detects smoke and has to be connected to a fire alarm system control panel to trigger off an alarm.
If you refer to SCDF’s website, you will notice their terminology is HFAD (Home Fire Alarm Device). They do not refer to as home fire Detection device, because the audible alarm is the crucial part to get people’s attention of a fire risks. Remember that a smoke detector only detects smoke and it can only sound off an alarm if it is connected to a fire alarm system control panel.
The reason why it is not referred to as a Home Smoke Alarm Device is that there are other non-smoke alarms that can be used to detect fire risks such as carbon dioxide alarms, heat alarms.
All said, you will notice most people actually refer to smoke alarms as smoke detectors. So to make life easy, we will also use smoke alarms and smoke detectors interchangeably here.
Now quiz your friends about this today. Be that smoke alarm expert within your group!
Which is better - standalone smoke detector or interconnect / interlink smoke detector?
As the name implies, a standalone smoke detector is an individual smoke detection unit. It does not trigger other nearby smoke detectors. On the other hand, interconnect (or interlink) smoke detectors work together in a cluster. When one detects smoke, not only will it sound off the alarm, it will also send a signal to all interconnected smoke detectors to get them to sound off as well.
Interconnect smoke detectors are best deployed in large homes, in excess of 1300 square feet, eg: dual key condos or multi storey homes such as landed, penthouses, maisonettes. The idea is when a fire risk occurs in 1 corner of the home (eg backyard), occupants, at the other end of the home (eg 2nd floor), are notified much earlier, instead of until smoke reaches the smoke detector nearest to their location. By then, the whole home may already be filled with dense smoke, making escape a lot harder or impossible.
Interconnect smoke detectors communicate with each other on either the frequency band of 433MHz or 868MHz, with the former being the more common one. The main difference between the frequency bands are distance and interference.
433MHz frequency band has been widely used in almost many control applications, while 868MHz is exclusively reserved for communication between wireless sensor networks. Since many wireless products utilize 433MHz band, which can lead to interference/disturbance of communication between different products. 868MHz band is exclusively opened for wireless alarm system, it's less likely to be interfered.
However, signals with longer wavelengths (lower frequency) travel a greater distance and penetrate through, and around objects better than signals with shorter wavelengths. Higher frequencies result in shorter wavelengths. As such, a cluster operating in 433MHz may be better suited, especially in Singapore's context where homes have plenty of concrete walls.
Because of the additional networking circuitry, interconnect smoke detectors generally cost more than that of standalone. That said, they are still affordable, costing in between $100-$200 per piece. As smoke detectors are designed to work over 10 years, the annual cost still works out to be $10-$20, which is around 3 to 4 cups of Starbucks coffee or bubble teas.
What are the types of smoke detectors?
The 2 broad types of smoke detectors are that of photoelectric and ionization. There are plenty of information online about how these 2 types of smoke detector work, so we will briefly introduce the mechanics and not go deep. What you should know are the pros and cons of these 2 types of smoke detectors.
Photoelectric smoke detector (quoted from Wikipedia)
A photoelectric smoke detector contains a source of infrared, visible, or ultraviolet light, a lens, and a photoelectric receiver. In some types, the light emitted by the light source passes through the air being tested and reaches the photosensor. The received light intensity will be reduced due to scattering from particles of smoke, air-borne dust, or other substances; the circuitry detects the light intensity and generates an alarm if it is below a specified threshold, potentially due to smoke.
In other types, typically chamber types, the light is not directed at the sensor, which is not illuminated in the absence of particles. If the air in the chamber contains particles (smoke or dust), the light is scattered and some of it reaches the sensor, triggering the alarm.
Click here to find out how our standalone photoelectric smoke detector (OSD-01) works in detail.
Ionization smoke detector (quoted from Wikipedia)
An ionization smoke detector uses a radioisotope to ionize air. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm.
There are also other types of (non-smoke) alarms:
- Carbon Monoxide
- Carbon Dioxide
We will not discuss these other types of alarms as they are less common and less relevant in our context.
What is more important are the following:
- Photoelectric smoke detectors respond many times faster to fire in its early, smouldering stage (before it breaks into flame) than that of ionization smoke detector.
- Ionization smoke detectors respond slightly faster to fast flaming fires than photoelectric smoke detector.
- Under UL test conditions, ionization alarms consistently respond about 30 to 90 seconds faster to open or “fast-flame” fires than photoelectric smoke detectors. Ionization alarms respond on average between 15 to 50 minutes slower in a smoldering fire than photoelectric alarms.
- With the exception of kitchen where grease/oil fires are a possibility, most residential fires started from smouldering fires. Think overloaded power supplies, cigarettes on sofa, overcharged electronics etc where you will see dense smoke being produced before breaking into flames.
- The vast majority of residential fire fatalities are due to smoke inhalation, not the actual flames. Nearly 2/3’s of fire fatalities occur at night while you sleep.
- Today, all furnishings and a large percentage of the building materials are synthetic materials which burn significantly faster than natural materials. In tests, a room with furniture built from natural material took 29 minutes to be decimated by fire while a room with furniture built from synthetic material took only 3 minutes and 30 seconds to be completely decimated by fire.
- Ionization are more prone to false alarms due to their mechanics and as a result more likely to be intentionally disabled.
The summary, if the above is still too much to absorb:
- Most residential fires are of smouldering type, characterized by the production of dense smoke before breaking into flames.
- Statistically, smoke kills more than fire itself.
- Today, most furniture at home are built from synthetic materials which burn fast. Tests have indicated it is possible for a house to be completed decimated in a few minutes, which means one has less time to escape in the event of fire.
- Ionization smoke detector takes 15 to 50 minutes longers than the photoelectric counterpart when it comes to smouldering fires. And remember today’s houses can be decimated in minutes. You do the math.
PHOTOELECTRIC smoke detectorS ARE MORE EFFECTIVE AGAINST SMOULDERING FIRES
Smoke kills more than fire. A smoke detector that detects smoke quicker gives residents a much higher chance of escape.
Above are extracts from an article titled “Silent Alarms; Deadly Differences”, published by Skip Walker, an ICC Certified Combination Residential Building Inspector, an ICC Certified California Combination Residential Building Inspector, a CREIA Master Inspector (MCI), an ASHI Certified Inspector (ACI), and a FIRE Certified Fireplace Inspector.
For the interested, you can click on this link to see his extensive deck on the comparison between photoelectric smoke detector and ionization smoke detector.
Watch the video on the much-delayed response time of ionization smoke detectors in the case of smouldering fire.
Is a dual/combi smoke detector which are both photoelectric and ionization better?
The response depends on who you talk to. We strongly believe in photoelectric only smoke detectors being the more suitable smoke detectors for residential use. You can read more of the comparison in this Question.
While a dual smoke detector does have the benefits of both photoelectric and ionization smoke detectors, it also inherits the cons of an ionization smoke detector, specifically the increased rate of false alarms.
Ask yourself this question: if this dual smoke detector keeps triggering false alarms, what are the chances that you will assume it’s “another” false alarm the next time the alarm goes off in the event of a real fire risk? Think “cry wolf”.
Or worse, deactivate/remove the whole alarm completely?
“If you take something that works and combine it with something that doesn’t, how can the combined device be better?”
When the test button on the smoke detector is depressed and the alarm goes off, it means the smoke detector is functional.
What the test button does, when depressed, is to trigger a signal to the smoke detector circuitry to sound off the alarm. It does not mean the sensors, be it photoelectric or ionization, are functioning properly.
To verify if the sensors are indeed functional, you will require to do an actual test with smoke, which is highly not recommended because of these reasons:
- Dangerous to produce smoke from fire at home.
- Smoke particles might have accumulated within/on the smoke detector sensors, potentially rendering the sensors inoperable in the event of a real fire. In the unfortunate event of fire at home, even if the damage is minimal, it is recommended to replace the smoke detector.
If an actual test is not recommended, how then does one verify if the sensors are functional?
This is the reason why it is important to only purchase and install smoke detectors that are certified in compliance to either EN 14604 (European standard) or UL 217 (American standard) or AS 3786 (Australian standard).
PURCHASE smoke detectorS THAT ARE CERTIFIED IN COMPLIANCE TO EN 14604
This device is meant to raise an alarm in event of fire. Don't risk having the smoke detector not sounding off when your whole family is asleep.
You may then wonder then what is the purpose of testing the smoke detector? The test serves 3 purposes:
- To verify that there is still power to the alarm circuitry.
- To verify that the alarm circuitry is functional to produce the high pitched alarm sound.
- To let family members be reminded how a smoke detector’s alarm sounds like. There have been events where the alarm went off and the household members had no idea what was creating that sound.
Hence, while testing the smoke detector does not guarantee the sensors are functioning properly, it is still important to test it regularly. We highly recommend monthly tests.
MONTHLY TESTING OF smoke detectorS
Given the frequency of such tests and smoke detectors are typically mounted on ceilings, we recommend to purchase smoke detectors with big and easy to reach test buttons. This way, you can use a stick to reach up to depress the test button instead of having to get a stool/ladder to try to reach the test button.
BIG AND EASY TO REACH TEST BUTTONS
Instead of having to climb on ladders/stools, you can use sticks to easily reach test button to conduct regular smoke detector testings and/or muting smoke detector in false alarms.
On the same note, a big and easy to reach hush button is also helpful in the event of muting the alarm in the event of a false alarm.
How frequent does the batteries of a smoke detector needs to be changed?
This varies from model to model but are usually either powered by a 9V battery or a lithium battery.
In the case of a 9V battery, it boils down to the current drawn by the smoke detector and the brand/type of battery used. An inferior battery is likely to last much shorter than a reputable brand. The typical duration can be anywhere between 6 months to 2 years.
On the other hand, a smoke detector powered by lithium battery requires less changes. In fact, most of such smoke detectors use specific lithium battery determined by the manufacturer.
The best form of lithium battery powered smoke detectors would be those where the lithium battery is sealed-in, non-rechargeable and non-replaceable and where their certification includes testing and verification of the built-in battery’s lifespan to be up to 10 years. One such certification would be the VdS 3131 certification.
SEALED-IN, NON-RECHARGEABLE AND NON-REPLACEABLE LITHIUM BATTERIES PREFERRED
Saves you the hassle of having to know what type of batteries to buy for replacement.
All smoke detectors should have a feature to warn on low battery, usually accompanied by audio beeps. This feature is to help remind you to replace the batteries. But you can imagine these additional beeps are simultaneously draining its already low power. So if you still choose not to give it a fresh set of batteries, it will eventually give up on you (power fully drained) and as much as it wants to, it can no longer be on the lookout for smoke and fire risks for you and your family.
To circumvent these uncertainties, regular testing of smoke detectors are recommended (we say it is a must). A monthly test would be sufficient. All smoke detectors will come with some form of test button. To test, simply depress the test button and one should hear the alarm going off.
Do note that this test only confirms the circuitry is to sound off the alarm is functional. It should not be interpreted that the sensors are functioning properly. Read this Question to learn more.
If a smoke detector uses a sealed-in, non-replaceable battery, what can one do if the smoke detector fails in the test (no alarm heard) or showing low battery warning before its claimed battery life?
Clearly, it will not be possible to replace the battery oneself since it is non-replaceable. There are only 2 options available:
Contact supplier for repair or exchange if there is still warranty coverage.
Throw away the smoke detector and replace a new one.
For peace of mind, it is recommended that one only purchases such smoke detectors from suppliers that offer a warranty period as long as the claimed battery life, eg a 10 years warranty period if the battery is claimed to have a 10 years life.
INSISTS ON A WARRANTY PERIOD AS LONG AS THE CLAIMED BATTERY LIFE
Peace of mind by getting from suppliers who offer a battery warranty period as long as the claimed battery life.
Should I get a battery powered smoke detector or one that connects to the mains?
There are 2 types of power sources, wired or batteries.
One may think that a wired version is better since there is no hassle of battery replacement. This is quite the contrary as most, if not all, wired smoke detectors do require battery as a form of backup, in the event of a power outage. By design, these alarms will fall back on battery power supply. However if the batteries are dead as well (or worse, not even installed in the first place), then the smoke detector will not detect smoke and sound off the alarm.
This is potentially a fatal situation if the fire breaks out in the night when everyone is sleeping.
In terms of ease of replacement, battery powered smoke detectors are definitely recommended over wired ones since one simply take down from their mounting positions and put up a new set in place, usually by double sided tapes or magnetic plates. Replacement of a wired version usually requires getting the same model or a model that uses the same power connector. In cases where the mains are directly connected to the smoke detector without a connector, replacement requires the engagement of a qualified electrician, not something an untrained individual should attempt.
A BATTERY POWERED smoke detector IS GENERALLY PREFERRED OVER A WIRED ONE
Ease of physical alarm installation and replacement.
There may also be new areas in your home that you might want to install additional smoke detectors after you move in. Having to engage an electrician to relay power cables from mains to your desired location is going to cost, not to mention, unsightly power cable trunkings running across your beautiful home.
In consideration of the above, a battery powered smoke detector is generally preferred over a wired one.
Does a smoke detector ever need to be replaced?
A definite yes! It should be replaced when either scenario happens:
- In the unfortunate event of a fire, regardless of how little damage caused by fire, the smoke detector should be replaced with a new set.
- 10 years after manufacturing date. The smoke detector should come with a “date of replacement” or equivalent, usually at the underside of the smoke detector itself.
- If the smoke detector displays visual / audio signs of fault warnings, despite a fresh change of batteries in the case of alarms with replaceable batteries. Get a new set if there is still warranty.
It is not advisable to continue using the alarm if any of the above scenarios is triggered.
I see some of the smoke detectors have certification labels beyond EN 14604, UL 217 and AS 3786. Are these certified as well?
There is no quick answer to this without seeing the actual certification label. You can think of EN 14604, UL 217 and AS 3786 as the benchmark of smoke detector certification standards. There are private certification vendors including but not limited to VdS, TÜV, Setsco, who will set up their own standards that comply to the benchmark standards or even higher.
VDS 3131 HIGHER THAN EN14604
Includes corrosion endurance testing & 10 years battery service life testing.
One instance would be VdS, with the VdS 3131 certification not just being compliant with EN 14604 standard, but also having additional requirements, which includes but not limited to:
- Corrosion endurance testing
Now, this would make perfect sense since a corroded smoke detector’s sensors are unlikely to perform at its optimum, if they even perform at all in the first place.
- Battery service life for alarms that come with non-replaceable batteries
Given the non-replaceable nature, alarms with this certification give assurance on the claimed battery service life.
You can refer to this link if you are keen to find out more about the VdS 3131 certification process.
Can a smoke detector be mounted on the wall instead of the ceiling?
Smoke always rises and spreads out upon hitting a barrier such as a ceiling. With the smoke detector mounted on the ceiling, it will be able to detect the spread-out smoke and sound off the alarm. Hence ceiling is always the optimum location for mounting.
Do note that it still needs to be mounted more than 4 inches from the wall / corner. This is to avoid the dead air space.
Dead air space is a reference to the areas in a house where air gets trapped and prevents the smoke detectors’ ability to detect the smoke. In a fire, smoke travels by rising up the surface of walls. If the smoke is rising up against a surface with a sharp turning point, then the smoke will not rise to the turning point. It will instead roll on top of that pocket of trapped air. A smoke detector mounted within the dead air space will never be triggered since smoke will not reach it.
If the layout makes it difficult to mount on a ceiling, such as when one has a pitched ceiling instead of flat ceiling, it is possible to mount on a wall, provided it is mounted between 4 inches (due to dead air space) to 12 inches from the ceiling/wall line or apex.
** Above diagrams are from NFPA 72.
Please note this link requires you to create a profile with NFPA first to access the document.
Where to install smoke detectors?
The rule of thumb is installing them along the escape path of your fire plan. SCDF recommends installation on the ceilings of the living room, internal corridors or staircase entrances. Additional smoke detectors are also suggested to be installed in other places such as bedrooms for additional protection.
As such, for a single storey home, we recommend installation of 1 at the center of the living room and 1 along the corridor leading to the rooms.
SINGLE STOREY HOME: 1 AT THE CENTER OF THE LIVING ROOM AND 1 ALONG THE CORRIDOR
For multi storey home, we recommend installation of 1 at every storey and if the circulation area of the storey exceeds 70 square meters, at least 2 smoke detectors to be installed.
MULTI STOREY HOME: 1 AT EVERY STOREY OR 2 IF AREA EXCEEDS 70M2
Other than dead air space, what other places to avoid installation of smoke detectors?
In general, smoke detectors are to be located along the planned fire escape path. Every house fire escape path will differ. However there are certain areas that you need to be mindful of in for the smoke detector to perform optimally and reduce chances of false / nuisance alarms.
If you do not know what is dead air space, refer to this Question.
There are certain locations that are notorious in creating false alarms (aka nuisance alarms) for smoke detectors, something you want to actively avoid. A couple of false alarms may result in you or your family ignoring a real alarm that can have devastating consequences.
Here’s a non-exhaustive list:
Near open windows / doors or windy areas where particles from outdoors, such as smoke from a barbecue, heavy pollen, insects, or dust as these have a higher rate of causing false alarms.
In bathroom or steamy areas. It should be highlighted that steam is not smoke, however an unusual large volume of steam / high humidity may break the internal circuit, which then triggers false alarms.
In kitchen where cooking combustion particles often from stove spills / broiling / searing enter the smoke detector and trigger it. If you must, install a photoelectric smoke detector instead of an ionization smoke detector and at least 3 meters away from all cooking appliances.We recommend heat alarms as an alternative to smoke detectors in kitchen as heat alarms are designed to detect an increase in temperature and are insensitive to smoke.
Dusty / greasy areas where buildup of dust / grease around the smoke detector is significantly faster, thus reducing the effectiveness of the smoke detector detecting smoke, or worse rendering it totally incapable of smoke detection. Similar to kitchen, heat alarms are more suitable in such areas.
Near altars where incense sticks are burning. Install at least 3 meters away from the altar.
In insects infested areas where insects buildup, dead or alive, can trigger a false alarm.
It is also worthy to note the following as well:
Ambient cigarette smoke does not trigger off a smoke detector, unless it is deliberately blown into it.
Insects fogging may trigger off a smoke detector, more of an ionization smoke detector, than a photoelectric one. One option is to temporarily cover the smoke detector with a dust cap or bag, but use a bright color one so that you will not forget to remove the cap / bag when the fogging is completed. The other option is to mute the alarm while the fogging is taking place. Most smoke detectors have a period of mute (around 10-15 minutes) when the hush button is depressed.It is also wise that the hush button is easily accessible via a stick, instead of having to climb on a stool or ladder to press it, a good reason for having big, accessible hush buttons.
I know a smoke detector is important, but it does not fit my decor. Can I paint over it?
Would you normally paint over your A/C (aircon)? I guess you would not. The same would apply for smoke detector. The issue with painting over the smoke detector is that the latex paint may cover up some of the vents that the smoke detector depends on to detect smoke.
You may have seen some properties with seemingly painted smoke detectors. Those are likely done by professionals, although we still don’t recommend it.
An alternative is to consider models where they are aesthetically designed, instead of the ugly white plastic round slab.
I know I cannot paint over a smoke detector, but can I install in locations, eg behind pillars, so that it is out of sight?
The answer depends a lot on your home layout. If it is installed at least 4 inches (~ 10 cm) behind the pillar to avoid dead air space, it may be plausible. The assumption here is the location is along the escape path you have planned.
That said, you can always consider models that are aesthetically designed so that you do not have to hide them.
After all, these are life saving devices and they should be installed where they can perform optimally.
Why the need to do regular maintenance on a smoke detector and what are the best ways to do so?
If you own a car, it is common practice to do regular maintenance every 10000km or so, with the intent to keep the car performance optimum. Likewise to the maintenance of a smoke detector, where the intent is to ensure the smoke detector is always ready to detect smoke and sound off the alarm.
Just like you would not want your car to break down while driving, you would not want your smoke detector to not be able to detect smoke in the event of a fire risk.
Think about it. Your smoke detector sits quietly on the ceiling, not moving. It is natural that dust / cobwebs will collect on your smoke detector, especially if it is installed in a location that is more dusty or humid.
Dust on smoke detector is akin to mud on your car’s windscreen. When there is too much mud on your windscreen, you probably will not see where you are going and likely to get into an accident. Similarly, dust / cobwebs buildup on smoke detector clouds its sensors, lowering its effectiveness of smoke detection.
The good news is maintenance of a smoke detector is much easier than the maintenance of a car. You can do it yourself and do not require a skilled technician. All you need is just a vacuum cleaner or a canister of compressed air. Or a duster if you do not have a vacuum cleaner.
To clean the smoke detector, you would thoroughly vacuum out the entire area between the front cover and the backplate, all the way around the perimeter with the crevice tool or soft brush attachment of a vacuum cleaner or blow through the same gap with compressed air.
Some smoke detectors comes with a detachable housing (where batteries are placed) which you can detach and perform the same cleaning procedures.
Is there a better way, you may ask. There are certain models of smoke detectors that are anti-dust, anti-insects by design. We recommend such smoke detectors as you only need to vacuum the exterior of the smoke detector and not have to deal with removal of housing to clean the inside.
ANTI-DUST, ANTI-INSECTS smoke detectorS
Maintenance as easy as vacuuming the exterior of the smoke detector and not have to deal with removal of housing to clean the inside.
Is there a way where I do not ever need to maintain the smoke detector may be your next question. There isn’t unfortunately. Anti-dust smoke detectors, while minimizing the buildup of dust / cobwebs around its sensors, do not and cannot prevent the buildup around its exterior.
Also, the smoke detector is always on the lookout for smoke for you and your family, 24 hours a day, 365 days a week. Surely you can spare a few minutes to give it a clean up for the undying dedication it has provided? Even plants require weekly watering, in this case, it is only asking for a few minutes in the entire year.
Alright, how often then? A yearly cleaning is recommended to ensure optimum performance of the smoke detector. You can combine this activity with the replacement of batteries if you have one which uses the 9V battery.
Obviously, this requires deliberate discipline and we recommend you to set a yearly reminder for this. With today’s technology such as Google Calendar, it is very easy to set a yearly reminder.
Is constant beeping/chirping normal?
Of course it is not normal. Anything that is beeping, is essentially trying to get your attention. It could be a weak battery or a fault that it has detected. It is important that you diagnose the root cause by referring to your smoke detector manual now. Typically, the manual will have a section on troubleshooting that lists down the various types of issues, together with its respective sequence of beeps and/or visual flashing cues.
If you cannot solve or diagnose the issue, you should call your supplier’s support for further assistance. It may require a replacement of the smoke detector.
Stopping false / nuisance alarms
smoke detectors, at the end of the day, are electronic devices, programmed devices to detect smoke. They do not throw tantrums nor have bad days.
If you keep experiencing false alarms, it is likely that something is “disturbing” it. You should quickly identify the source and resolve it. The last thing you should do is to deactivate the smoke detector, remove the batteries or just mute the alarm without checking if there is indeed a fire risk.
Triggers of false alarms fall into 2 big categories:
A smoke detector is triggered, what should I do?
First of all, try to ascertain if it is a false alarm by checking common spots of fire hazards, eg stoves, electrical outlets/points etc.
If the fire source is identified, decide if you have the means, eg, fire extinguisher or fire blanket to put out the source. Remember, today’s homes are largely furnished with furniture built from synthetic material that burns fast. A fire may spread across the whole house in less than 2 minutes.
If not, execute your fire escape plan immediately!