Smoke detector knowledge

(1) How does a smoke alarm work?

The smoke is moving upward and reaches the bottom of the sky. Smoke alarm found fire through the smoke. When you don't see the flame or smell the smoke, the smoke detector is already known. It keeps working, 365 days a year, 24 hours a day. At the time of the alarm, it shrieked until the smoke dispersed. In a real fire it worked until it was burned.

There are two kinds of sensors available for independent smoke alarms in residential houses: one is an ion sensor and the other is a photoelectric sensor.

Ion sensors work by measuring the balance of positive and negative charges in the air. Inside the sensor, there is a small piece of radioactive material that generates a tiny current in the air flowing through the sensing chamber. On the circuit board, there is a computer chip to monitor this current. When the smoke particles enter the sensing chamber, the balance of positive and negative charges will be disturbed, and this current will also change. As smoke gradually increases, the imbalance between positive and negative charges increases. When this balance reaches a certain limit, the horn will sound.

Photoelectric sensors measure the concentration of smoke through a beam of light and a light sensor. When the device is designed, the beam is off the sensor. When smoke enters the sensing chamber, the smoke particles scatter some of the light beam onto the sensor. As the concentration of smoke gradually increases, more light is scattered onto the sensor. When the beam reaching the sensor reaches a certain level, the buzzer will sound.

(2) How to reduce false positives is a very serious problem. When the fire does not happen, the smoke alarm constantly alerts you and you may withdraw it, so that when the fire does occur, no alarm will be issued.

The causes of false alarms are sorted in order of: 1. Cooking 2 Effects of vapor or moisture 3 Smoke from cigarettes 4 Power supply 5 Dust 1 Many false alarms for cooking-generated smoke are emitted by ion alarms. Because the sensor is sensitive to tiny smoke particles, even particles that are invisible to human eyes. The smoke particles produced by cooking heat are invisible to the human eye.

There are two basic solutions. The location of the mobile alarm. Placing the alarm farther away from the cooking area will make the cooking fumes become thinner as they arrive at the alarm, reducing false alarms. However, this method does not always work, especially when the air flow will bring cooking smoke to the alarm. Therefore, when moving the alarm, be sure to first understand the flow of air.

The second way to solve the problem is to replace the alarm, a is to buy a new ion alarm with a mute button. The alarm will stop for 15 minutes as soon as a button alarm is triggered. This will allow enough time for cooking-generated smoke to diffuse. b choose to buy a photoelectric smoke alarm. Photoelectric alarms are less sensitive to tiny smoke particles, so there is no false alarm for cooking smoke particles.

2 Steam or moisture will condense on the sensor and the circuit board. If too much water vapor is condensed, an alarm sound will be emitted.

Solution: Install the alarm device away from vapor and moisture. For example, the alarm should not be installed in the corridor of the bathroom. This can solve the problem. However, if the alarm is supposed to work properly and it now reacts to steam or moisture, the problem may be the cause of the alarm's aging. Older alarms become more sensitive and easier to respond to steam and moisture. Therefore, the occurrence of false alarms may also be due to the fact that the alarm exceeds the service life and needs to be replaced.

3 In general, smoke alarms do not respond to cigarette smoke unless the smoke produced is very strong. For example, many smokers who smoke in the same room may cause an alarm. If the alarm is too old, it will respond even if the smoke concentration is low. Therefore, on the contrary, we can also judge whether the alarm has been aging.

4 When the battery is nearly empty, it will make a buzzing sound every about one minute (different models may have different intervals and sounds, but they all have a low battery warning function). Some people think that this is a false alarm. .

But this kind of sound is very different, because it sends a single, short sound, and it sounds about once every minute. If your alarm sounds intermittently, you can replace the battery to see if it solves the problem.

5 If the alarm constantly sounds an alarm, then there may be too much dust in the alarm. Consider replacing the alarm or cleaning it. When cleaning the alarm, vacuum the dust collector one by one near the alarm opening. The dust that accumulates in the alarm can be completely removed.

(3) Is it safe to use smoke alarm?

As the number of users of smoke alarms continues to increase, the number of deaths due to residential fires continues to decline. According to a report from the National Fire Protection Association, once a fire has been installed in a residential building equipped with a recommended number of smoke alarms, the chances of escape for the people in the house will be 50% higher than those for unsold houses.

(4) Do I need to replace my smoke alarm?

If the expiration date of the smoke alarm is close to 5 years, its useful life is about to end and should be replaced. Some people think that their smoke alarm will only work when there is smoke. In fact, it is always in working condition, monitoring the change of air 24 hours a day. For example, the ion smoke alarm will cycle 1.75 million times in five years. Photoelectric smoke detectors work 24 hours to check the smoke particles in the air.

Just like other electrical devices, smoke alarms will be lost over time. A smoke alarm that has been used for 5 years will degrade fire detection, so it is better to replace it early.

(5) How many smoke alarms do you need to install at home?

The average family needs to install at least one set of smoke alarms. The specific number is determined by two factors. The number of dwellings and the number of bedrooms.

The following suggestions are based on the standards for home fire alarms published by the National Fire Protection Association of the United States:

For new homes, the standard requires a smoke alarm in each bedroom.

One is also installed outside the bedroom and across the door to hear the alarm.

At least one is installed on each floor in the house.

It is necessary to install an alarm in each bedroom. There are many fires that occur in the bedroom. The closer the alarm is to the fire, the more likely it is to have an alarm.

The purpose of installing a smoke alarm outside the bedroom is to remind the sleeper that there has been a fire outside the bedroom. If the bedroom is located in different locations in the house, smoke alarms should be installed in different places.

If the house is large, more than one smoke alarm can be installed on different floors.

Smoke alarms are found through smoke, and the closer they are to fire, the quicker they can respond. Therefore, installing more smoke alarms will increase your security.

(6) Where in the house does not need to install smoke alarm?

For extremely hot or cold places, or where there is often a lot of smoke and dust, and on the top floor and similar places, the use of alarms is not recommended. The manufacturer's instructions will tell you where these devices are suitable for.

Smoke alarm does not apply to the garage for two reasons: First, the garage is not affected by the outside temperature, so it sometimes deviates from the alarm temperature range. The second reason is that the gas emitted by the engine can cause false alarms.

Another place where smoke alarms do not need to be installed is the kitchen. If the alarm is installed too close to the cooking appliance, false alarms may result. NFPA 72 requires that when the smoke alarm is installed within 20 feet of the cooking appliance, a photoelectric device or stationary button should be installed at the same time.

(7) Which kind of smoke alarm is better?

Each type of alarm has reached the test standard, but they each have their own strengths.

Ion alarms are quicker to detect tiny smoke particles. When an open fire (such as a burning newspaper) and a rapidly burning blaze fire, there are more tiny particles of smoke in the air, and the ion alarm will alarm first than the photoelectric alarm.

The photoelectric alarm for relatively large smoke particle induction faster, smoldering (such as cigarette lit sofa), the larger particles of air in the air will be more, then the photoelectric alarm than the ion alarm first alarm.

The time interval between these two types of alarms is not large, but many fires are spreading very quickly, so time is crucial for saving lives.

(8) What methods can I use to detect smoke detectors?

Each smoke alarm has a check button after it is produced. Manufacturers recommend that you always check your alarm regularly, at least once a month.

(9) Should I use real smoke to detect smoke detectors?

This method is not advocated because the burning of the smoke can cause the fire to actually occur. It's very dangerous. Usually there is a lot of combustibles in the bedroom. The open flame can easily cause an accidental fire. Using the test button is the best method.

(10) Is it important to clean the alarm frequently?

It is necessary to clean the alarm regularly. Smoke alarms have small screen-like covers around the sensing center to prevent outside bugs and dust from entering the sensing center. However, dust can accumulate around the shelter and delay the movement of air. Cleaning the alarm is very easy. Just use a vacuum cleaner to suck out the air outside the alarm, and clean it at least once a year.

(11) How to use the battery?

Smoke alarm battery can be used for at least one year in normal circumstances. The biggest reason for smoke alarms to stop working is due to man-made removal of batteries - perhaps for weak electrical signals or for the suspension of false alarms - and later forgetting to put them on. New smoke detectors have added a spring switch that can't be used to replace the smoke detector without a battery. A very important improvement.

(12) Is the battery life of 5 years a good idea?

A battery with a 10-year service life is installed in the smoke alarm to reduce the frequency of battery replacement. A 9-volt lithium battery can be used. But still must be tested regularly.

(13) Is the radiation of ionized smoke detectors dangerous to the human body?

Will not. Ion alarms using a small amount of 241 do not create any danger. It is less energy than the radium used in the watch dial. The radiation intensity is approximately 1 Curie, or less. The range of the ray is very short, much less than 1 meter; penetrating power is very weak, a white paper can block it.

In fact, you can discard the old alarm in the trash without worry. When you hear that the ion smoke alarm is dangerous, it is completely groundless. When the ion alarms were just produced, the federal government tested them. As a result, they did not pose any danger to consumers. After several years of testing, the federal government confirmed that the alarm was indeed safe.