Superlative Smoke Detector

Sean T.


The purpose of the experiment is to understand which smoke detector reacts faster in certain situations such as fire and smoldering smoke. Another purpose is to understand where to put the smoke detectors in order to achieve the most effectiveness. The objective of this experiment is to find out which of three smoke detectors; Ionization, Photoelectric, and Dual Sensor to install and where to install them to ensure the safety of one’s family and one’s self.


Smoke detectors unnoticably save many lives. The casualties each year were 1 every 190 fires with present smoke detectors, compared to 1 every 85 fires when smoke detectors weren’t in use. To decrease the casualties rate, it is best to know which smoke detectors are the most dependent in certain situations. The most primarily used smoke detectors are Ionization, Photoelectric, and dual sensor, a combination of the two. In order to know which works best, it is important to know how each detector works, and in which situations.


Ionization smoke detectors are the least expensive of the three, and very effective. They work using chemical reactions that occur inside the detector. The ionization chamber is open to air and is filled with ions. Ions are atoms that have lost electrons to make positively charged nuclei. A small amount of Americium is present inside the chamber, and is constantly spewing out tiny radioactive particles called alpha particles, which leak into the detection chamber. As they do so, they collide with air molecules and turn them into positively charged ions and negatively charged electrons. The ions and electrons move in opposite directions between two electrodes. A current flows between the electrodes and a circuit, just as long as the ions and electrons are moving. This is how the smoke detector stays silent. However, once a fire breaks out, the smoke particles get into the detector and start to clog up the ionization chamber. The smoke particles will attach themselves to the ions and shut off the electrical circuit. The circuit in the detector spots that change straight away and sounds the alarm. Once the fire is put out and the smoke clears, the chamber clears, the ions travel back and forth between the electrodes as before, the circuit shuts down, and the alarm stops sounding.

Photoelectric smoke detectors are a big choice for stores, warehouses, gyms, and anywhere a big room is present. They come at a decent price, but if your life depends on it, ionization or dual sensor might be your best bet. Photoelectric smoke detectors work by emitting a light in one direction inside the detector, through an open hole on one side. Following the direction of the beam on the right is a sensor, emitting no beam of light. In order to sound the alarm, the beam of light being emitted must reflect into the sensor. When the light is neutral, it will shine straight forward, passing the sensor completely. But in a scenario where smoke is present, this smoke detector steps into the spotlight. When smoke flows through the hole and congests the path, the beam of light will reflect off of the smoke and straight into the sensor, sounding the alarm. When the smoke clears out, the beam of light will move away from the sensor and emit back in the original direction, shutting the alarm off. A major problem with photoelectric smoke detectors is the amount of smoke required to actually sound the alarm. It requires loads of thick smoke for the light to not penetrate the smoke, and instead reflect over to the sensor. It is not very efficient and can take longer to sound than other detectors.

Fire and smoke aren’t the only things that can set off a smoke detector. Users of ionization smoke detectors should avoid placing smoke detectors near restrooms, as the humidity from a shower may set off the smoke detector. Smoke detectors should be placed on each level of a household and should most importantly be installed near a kitchen, as that is where fire is worked with a lot. Smoke from pots can set off certain smoke detectors, which results in a nuisance alarm. A nuisance alarm is an alarm not set off by an actual fire. Occurrence of nuisance alarming usually results in removing the battery of the smoke detector or disconnecting. Worst case scenario the user forgets to reconnect the battery, and it ends with tragic consequences. Photoelectric smoke detectors can fix all that and can be placed in great proximity of the kitchen. A lot of steam from cooking is required to set them off as steam is thinner than smoke. Smoke detectors should be placed in each bedroom, for safety. If not, the fire will be able to spread for longer before setting off a smoke detector, and it is best to stop it as quick as possible.

The third and most versatile of the three smoke detectors is dual sensor. Dual sensor is a combination of both ionization and photoelectric. Because users are unable to choose which of the different detections to use and which not to use, that gives this detector its pros and cons. Judging by the design, people will think this is the most effective, but allocating space for 2 different detection methods is what makes this detector not as good as it seems. The reaction time may be decreased on one of the different detections, but it may increase the other. This cannot be used to counter nuisance alarm because of ionization built in as well. However, when the ionization alarm is delayed, photoelectric will make up for, and vise-versa. One kind will either exceed the other, or fall short of the other. But being good at many different tasks may not be better than being an expert at one certain task.


If the humidity of a room is modified and a fire is lit underneath 3 smoke detectors; ionization, photoelectric, and dual sensor, the dual sensor smoke detector will sense the fire and change in humidity and react (sound the alarm) the quickest because it contains 2 different kinds of smoke detectors in one unit.


3 different smoke detectors (Ionization, Photoelectric, Dual Sensor)

Journal (Record data)

Rack (Must have room on bottom for smoke to rise through; used for platform of smoke detectors)

Match (To light the fire)

50 Sheets of paper (Paper is to be crumpled up and set afire; 1 piece of paper per trial)



Humidity Monitor


Safety Precaution

Fire Extinguisher

Aluminum basket (Fire-lit paper is to be placed inside the basket to prevent fire spread to near vicinity)

Safety goggles (Protect eyes from fire/ smoke particles)



PART 1/2

Place the rack on a solid, non-flammable surface (Concrete)

Place the aluminum basket underneath the rack

In the order of ionization, photoelectric, and dual sensor, place the three smoke detectors from left to right on the rack

Crumple one sheet of paper and place it in the center of the basket

Light the paper using a match and start the stopwatches at that time

Listen for the first smoke detector to sound, record which of the three sounded first, and in how long

Record ONLY the times of the last two smoke detectors, and not the order

Once all smoke detectors have been set off, remove the aluminum basket and the items inside it

Once all the steps have been completed, find a small room indoors (Bathroom, bedroom), place the rack on the floor, and repeat step 3.

PART 2/2

If the room is more than 45% humidity, use a dehumidifier to decrease the humidity down to 45%. If the room is less than 45% humidity, use a humidifier to reach that humidity, and turn it off

Place the humidifier exactly 1 yard away from the smoke detectors

Power on the humidifier at max setting while simultaneously starting the stopwatches

Once the first smoke detector sounds, record which one sounded first, at what humidity it sounded at and how long it took to sound

ONLY record the times of the next 2 smoke detectors

If however no smoke detector sounds record it as 0 for time

Repeat part 1/2-2/2 to match the necessary amount of trials needed


Big image
Big image


Dependent variable- Time for smoke detector to set off/sound

Independent variable- Fire/Humidifier

Control group- No control group

Experimental group- 3 smoke detectors; Ionization; Photoelectric; Dual Sensor

Factors held constant- Humidifier settings to increase from 45%-60


The Hypothesis was somewhat supported as it states that the Dual Sensor smoke detector will react the quickest. Most of the time, the Dual Sensor reacted the quickest on part 1; when the fire was used, but on part 2 when the humidifier was used, it was mostly the photoelectric smoke detector that reacted the quickest to the humidity change. The purpose of the experiment was to see which smoke detector reacted the quickest in the scenarios of humidity change and a fire. The purpose was achieved as it is now known that the Dual Sensor smoke detector reacts the fastest in a fire because of its versatility, and the photoelectric smoke detector reacts the fastest to a change in humidity.


The Dual Sensor reacts the quickest to fire and the photoelectric reacts the quickest to humidity increase. The Dual Sensor contains both Ionization and Photoelectric smoke detection built in one, giving it the increased awareness to a fire. However, when humidity increases, the dual sensor may not specialize enough into it’s built- in photoelectric to sense it. The photoelectric smoke detector can sense the water particles in the air moving in through a small vent, which triggers the alarm, putting it slightly ahead of the dual sensor in that case. Along with that, the dual sensor reacts the quickest to fire, and the photoelectric reacts the quickest to humidity increase.


The Dual Sensor used the 2 combined smoke detectors in one and advantageously sensed the fires faster than the other smoke detectors, sometimes by over 1 minute. During part 2 of the experiment, the photoelectric smoke detector was able to sense the humidity increase because of its specialty in sensing visible gas (such as water particles in close quarters/fog, smoke, steam etc. and NOT carbon monoxide; not visible) using the light emitted inside it. On part 1 of the experiment. the least amount it took the dual sensor to sound was 0:48.54 which is about 1 minute less than the least amount of time it took the photoelectric smoke detector to sound. The least amount of time it took the Ionization smoke detector to sound was 1:20.02, which is still more than the dual sensor by 32 seconds. The data clearly shows that dual sensor is the ideal smoke detector for home use.

Reasoning/ Justification

The experiment was conducted to understand which smoke detector would react first to a fire and humidity change. To know which one was faster, it is necessary to examine the time each detector took before sounding. There are 3 essential times that are crucial to finding success in the experiment: 1) The lowest amount of time 2) The highest amount of time 3) The average amount of time. All of them tell the boundaries and assist in reasoning by placing walls that can’t be crossed, or eliminating useless information and help to think in the right direction. Those three times were examined and used to formulate the thought of which smoke detector would work best, and in what scenario, and after the experiment, it resolves the question that the ideal smoke detector for home use is the Dual Sensor Smoke Detector.


In order to prevent spread of fire into the near vicinity (such as a house), the experiment was to be done outside, which left the experiment susceptible to natural complications such as rain and wind which affected the life and growth of the fire. When the fire is affected like that, the results varied due to the wind pushing the fire away from the smoke detector, enlonging the time it took before the detector sounded. Crumpling the paper also affected the time it took for the smoke detector to sound as it made a different burning pattern and lessened or increased the time for the fire to fully light. This made some results unreliable.


The experiment applies to real life because it teaches the ideal smoke detector to install for home use and where and where to not install them to prevent false alarms. The results can be used to know exactly what sets off smoke detectors for real and as a false alarm. The results also can be used to let people know how long until a smoke detector senses a fire and which ones sense the fires faster and in what scenario. It is important that others know what I learned because it may save lives and homes.

A way to improve my experimental design would be to experiment with different types of fires. There are a lot of different kinds such as flaming fires, massive fires, smoldering smokes, and more. Many smoke detectors activate off the same cause, but there are many smoke detectors that activate from different causes. The best way to continue the experiment is to experiment with different fires that will not do harm to the experimenter or his/her belongings.