Smoke Detectors and Fire Alarms – Residential, Commercial, Industrial
Steve Maurer, IME
All homes and workplaces need protection from fire. It’s part of building codes everywhere. The type of system will vary depending on the type of building, number of occupants, and intended use of the structure.
It’s not my purpose to tell you what to install in your customers’ homes or places of business. The regulations are too varied for me to do that, but we can talk about some facts and figures. I also want to touch on some terminology that, while it may seem obvious, can make a difference when talking to customers.
First, let’s start with the difference between a detector and a fire alarm as I understand it. A detector senses the presence of a potential fire, while an alarm is a single annunciator or system used to warn occupants. In some cases, particularly in commercial and industrial settings, the alarm does more than just warn those in the building. It also may be tied to control measures such as sprinkler systems. And in many cases, it alerts emergency crews and other people who must be notified in the event of a fire.
We’ll get into how a detector senses smoke in a minute but consider this, most residential units are actually a combination detector and alarm, although they’re usually packaged as a smoke detector. I say this because they not only sense the potential presence of a fire, but also warn occupants of the dwelling, often with a loud beeping annunciator.
Some are also equipped with a voice alarm to warn of the fire. They cost a little more than signal-only detectors. But they may be worth the added cost. I know that when I’m awakened by a loud noise, it takes a few moments to get oriented. So the voice announcement will help clear my foggy mind.
Requirements for CO (carbon monoxide) detectors are being legislated in a growing number of municipalities and states across the country. Carbon monoxide is a poisonous gas that may result from a fire, but also from incomplete combustion in a controlled situation. Some sources of CO are generators, gas furnaces and heaters, stoves, and cracks in fireplace stacks.
Only half of the homes in the United States have a working carbon monoxide detector/alarm. But about 75% of U.S. homes have at least one potential source of CO. And according to the CDC (Centers for Disease Control) there are approximately 72,000 CO incidents each year in the United States.
If you’re servicing residential customers, it might be a good idea to educate them on these statistics and recommend installing CO monitoring equipment. It can be standalone units or integrated into the smoke detectors. Because of the way smoke detectors sense potential fires, they do not protect from carbon monoxide unless specifically designed for that.
How Smoke Detectors Work
No smoke detector is 100% accurate. There are some conditions that may alarm on a false positive. And other conditions may not detect a fire’s presence quickly. The two main forms of detection are ionization and photoelectric sensing. Some detectors and detector/annunciator units use both technologies.
In an ionization detector, a small amount of radioactive material converts air molecules into positive and negative ions. This conversion takes place between two tiny metal plates in a chamber (one positively charged and one negatively charged) creating an electrical circuit. When smoke particles enter the chamber, they disrupt the flow of electricity by bonding with the ions, thereby putting the device into alarm mode.
In a photoelectric sensor, there is a light emitter and receiver setup. There are two methods used, but basically smoke enters the detector chamber and changes the amount of emitted light detected by the receiver. It’s been shown that photoelectric sensors detect smoldering fires and fires from remote locations earlier than ionization detectors. In fact some state laws require photoelectric sensors.
The ionization detectors have their own characteristics that are better than photoelectric sensors for some situations. It’s often a good idea to either install both types in accordance with manufacturer’s instruction, or install the slightly more expensive dual sensor option that contains both technologies.
In fact, the NFPA recommends using both types of smoke alarm technologies for better protection.
In Commercial and Industrial Facilities, It Gets More Complex
While residential alarms usually cover just a few locations—bedrooms, kitchen, living room, etc.—and usually with separate detector/alarm units, commercial and industrial settings are more complex. There are more locations, often remote, that must be covered.
Sometimes these are set as zones, with one circuit cable connecting several detectors in each zone. Additional zones require additional cabling, one run per zone.
At other times, addressable detectors are used, giving a more precise indicator of exactly which detector is tripped. Multiple detectors in various zones can be connected to one cable since they are specifically called out at the panel. Often this cabling is ethernet wiring.
In either case, the signals go back to a control panel that’s programmed to act on each signal in a specific way or with multiple commands. For example, annunciators in that area might be sounded while HVAC is shut down and ventilators may help exhaust fumes. At the same time, emergency personnel and first responders may be summoned.
There are other concerns as well. In some hotels and office buildings, high ceilings can be an issue. Often as high as several stories above the main floor, these areas can be a challenge to cover properly, with sensors unable to reach the floor below.
In that case, aspirating detectors might be used. These sensors have drawtubes that sample at a lower level, or even several levels. Air samples are sucked up the tube, filtered and processed for indications of smoke particles, and then signals are sent back to the control/command panel if warranted.
These sensors are more sophisticated than other types, using multi-directional light scattering for photoelectric sensing and employing algorithms for smoke detection thresholds and particle type characterization.
Final Thoughts
No matter the location—residential, commercial, or industrial—smoke alarms and detectors are necessary, not just for the health of the building, but of the people inside, too.
Life safety systems should be the backbone of protections for life, property, and the overall environment. Make sure that the proper system is installed. And also ensure that preventive maintenance and routine testing are part of the package.
After all, if it doesn’t work … it won’t work when needed.
It’s not my purpose to tell you what to install in your customers’ homes or places of business. The regulations are too varied for me to do that, but we can talk about some facts and figures. I also want to touch on some terminology that, while it may seem obvious, can make a difference when talking to customers.
First, let’s start with the difference between a detector and a fire alarm as I understand it. A detector senses the presence of a potential fire, while an alarm is a single annunciator or system used to warn occupants. In some cases, particularly in commercial and industrial settings, the alarm does more than just warn those in the building. It also may be tied to control measures such as sprinkler systems. And in many cases, it alerts emergency crews and other people who must be notified in the event of a fire.
We’ll get into how a detector senses smoke in a minute but consider this, most residential units are actually a combination detector and alarm, although they’re usually packaged as a smoke detector. I say this because they not only sense the potential presence of a fire, but also warn occupants of the dwelling, often with a loud beeping annunciator.
Some are also equipped with a voice alarm to warn of the fire. They cost a little more than signal-only detectors. But they may be worth the added cost. I know that when I’m awakened by a loud noise, it takes a few moments to get oriented. So the voice announcement will help clear my foggy mind.
Requirements for CO (carbon monoxide) detectors are being legislated in a growing number of municipalities and states across the country. Carbon monoxide is a poisonous gas that may result from a fire, but also from incomplete combustion in a controlled situation. Some sources of CO are generators, gas furnaces and heaters, stoves, and cracks in fireplace stacks.
Only half of the homes in the United States have a working carbon monoxide detector/alarm. But about 75% of U.S. homes have at least one potential source of CO. And according to the CDC (Centers for Disease Control) there are approximately 72,000 CO incidents each year in the United States.
If you’re servicing residential customers, it might be a good idea to educate them on these statistics and recommend installing CO monitoring equipment. It can be standalone units or integrated into the smoke detectors. Because of the way smoke detectors sense potential fires, they do not protect from carbon monoxide unless specifically designed for that.
How Smoke Detectors Work
No smoke detector is 100% accurate. There are some conditions that may alarm on a false positive. And other conditions may not detect a fire’s presence quickly. The two main forms of detection are ionization and photoelectric sensing. Some detectors and detector/annunciator units use both technologies.
In an ionization detector, a small amount of radioactive material converts air molecules into positive and negative ions. This conversion takes place between two tiny metal plates in a chamber (one positively charged and one negatively charged) creating an electrical circuit. When smoke particles enter the chamber, they disrupt the flow of electricity by bonding with the ions, thereby putting the device into alarm mode.
In a photoelectric sensor, there is a light emitter and receiver setup. There are two methods used, but basically smoke enters the detector chamber and changes the amount of emitted light detected by the receiver. It’s been shown that photoelectric sensors detect smoldering fires and fires from remote locations earlier than ionization detectors. In fact some state laws require photoelectric sensors.
The ionization detectors have their own characteristics that are better than photoelectric sensors for some situations. It’s often a good idea to either install both types in accordance with manufacturer’s instruction, or install the slightly more expensive dual sensor option that contains both technologies.
In fact, the NFPA recommends using both types of smoke alarm technologies for better protection.
In Commercial and Industrial Facilities, It Gets More Complex
While residential alarms usually cover just a few locations—bedrooms, kitchen, living room, etc.—and usually with separate detector/alarm units, commercial and industrial settings are more complex. There are more locations, often remote, that must be covered.
Sometimes these are set as zones, with one circuit cable connecting several detectors in each zone. Additional zones require additional cabling, one run per zone.
At other times, addressable detectors are used, giving a more precise indicator of exactly which detector is tripped. Multiple detectors in various zones can be connected to one cable since they are specifically called out at the panel. Often this cabling is ethernet wiring.
In either case, the signals go back to a control panel that’s programmed to act on each signal in a specific way or with multiple commands. For example, annunciators in that area might be sounded while HVAC is shut down and ventilators may help exhaust fumes. At the same time, emergency personnel and first responders may be summoned.
There are other concerns as well. In some hotels and office buildings, high ceilings can be an issue. Often as high as several stories above the main floor, these areas can be a challenge to cover properly, with sensors unable to reach the floor below.
In that case, aspirating detectors might be used. These sensors have drawtubes that sample at a lower level, or even several levels. Air samples are sucked up the tube, filtered and processed for indications of smoke particles, and then signals are sent back to the control/command panel if warranted.
These sensors are more sophisticated than other types, using multi-directional light scattering for photoelectric sensing and employing algorithms for smoke detection thresholds and particle type characterization.
Final Thoughts
No matter the location—residential, commercial, or industrial—smoke alarms and detectors are necessary, not just for the health of the building, but of the people inside, too.
Life safety systems should be the backbone of protections for life, property, and the overall environment. Make sure that the proper system is installed. And also ensure that preventive maintenance and routine testing are part of the package.
After all, if it doesn’t work … it won’t work when needed.
