Ionization and Photoelectric Smoke Detection

It turns out, smoke detector does not necessarily equal smoke detector. As with any technology, the detection of smoke has evolved. The two most-used technologies are ionization and photoelectric. While both technologies sense the presence of smoke, the technologies are quite different. Smoke alarms for home, as well as smoke detectors for fire alarm systems employ these technologies. In this post we will explore the major differences between the two.

Smoke detection history

Smoke Alarm on Yellow Background

Many separate inventions ended up forming what we know as a smoke detector today. Fire alarms and smoke detectors used to be reserved for large commercial and industrial facilities, due to their cost and also size. The first affordable smoke detector with a battery was brought to market by the 1960’s. This detector was an ionization type detector. The technologies further advanced and allowed for the cost of the detectors to drop significantly to the levels we know today. The photoelectric smoke detector was invented in 1972, further advancing the smoke detector.


As the first invention for fire detection after the heat detector, Ionization minimized the time it required to sense a fire. Ionization uses a tiny amount of radioactive material, which ionizes the air. That is where the technology gets its name. The material used is generally Americium-241. The unit consists of two chambers. One chambers is free to the air and the other is a closed chamber. Both are exposed to the ionization and have two electrodes. the resulting current from the ionization between the electrodes is the same, until smoke enters the open chamber. It interrupts the flow of the current in the chamber and will cause an alarm condition.


Photoelectric detectors also have a chamber and look for obscuration of the air. That is where the similarities end. This technology employs a a source of light, usually emitted by a small LED and a receiver. This light beam is constant across the chamber. Should smoke enter the chamber, the light beam is interrupted and cannot be seen by the receiver anymore. It then causes an alarm condition within the detector. Photoelectric sensors are generally said to be more effective for smoldering fires, while ionization detectors shine for flaming fires.

What detector should you get?

Photoelectric detectors, being the most popular type detectors do provide adequate response to all types of fires. A recommendation is to purchase a detector that is multi-technology, such as a combination heat/smoke detector or a detector that combines the photoelectric and ionization technologies. While there is nothing wrong with a photoelectric only detector, it increases occupant safety to take it a step further. On that note, the ionization detector, while it contains radioactive material, uses Alpha radiation to ionize the air. This type of radiation has a very low penetration, which means it is stopped by the plastic around the detector and does not present a hazard.

CO Detectors

While on the topic, I would like to touch on carbon monoxide detectors, as they are closely related to smoke alarms. Many smoke alarms come as a combination unit with CO detection. CO detectors are a small chemistry lab. The presence of carbon monoxide causes a chemical reaction with an electrolyte and causes it to conduct electricity. This is an electrochemcial type CO detector. These detectors are highly effective, as they have a 5 to 10 year lifespan and are highly reactive to exact concentrations of carbon monoxide gas.

Detector Lifespan

Most smoke alarms and combination units have an expiry date printed on them. If your unit does not have an expiration date, we highly recommend it be replaced as soon as possible. Smoke alarms become less sensitive over their lifespan and collect dust, insects and other contaminants that can affect the effectiveness of the unit. Smoke alarms usually have a 10-year life, though that may differ for combination units. Most The detectors have a mechanism built in that will chirp the detector when its lifespan has been reached.


With Ionization smoke alarms containing radioactive materials, it is a good idea to return the unit to the manufacturer upon its expiration. While the radioactive material is generally not harmful and also considered safe to be disposed of in household waste, it’s a good idea to minimize the potential environmental impact. The manufacturer generally takes the detectors back for their internal recycling programs. Disposal information is usually printed on the back of the unit.

Our Services

We carry a large stock of smoke alarms and combination units. Our team can assist with replacement and the regular inspection of smoke alarms and detectors of all technologies. From new installations to replacement after 10 years, our units are a match for every application and will save lives in the event of a fire emergency.

The Fire Tretrahedron

Firefighter fighting fire

The Fire tetrahedron explains the basic elements that are required to have a combustion. A tetrahedron – sorry for the geometry lesson – is a triangle with four triangular sides. Think of a pyramid with a triangle as the base instead of a square. There are four basic elements required to have a fire. The tetrahedron is composed of four sides and is the further development of the fire triangle, which only shows the elements required for an ignition.

Fire Teatrahedron showing the four elements required for fire

The Elements of Fire

For fire to exist, the right conditions need to exist. These conditions are referred to as elements. These elements are oxygen, heat, fuel and the chemical chain reaction. In the tetrahedron the chemical chain reaction generally forms the bottom of the pyramid, with the other elements depicted on the sides. Most fire extinguishing systems, such as sprinklers, extinguishers and suppression systems work on the principle of removing one or more of these elements from the fire.


Without oxygen a fire cannot start, likewise, if the oxygen is removed fire cannot be supported. Technically this element should be referred to as an oxidizer, rather than just oxygen. Oxygen is the most common oxidizer, but combustion without oxygen is also possible. Fluorine is an example of another oxidizer that could support a combustion without oxygen present. Oxygen then really is an oversimplification, but for the purpose for the tetrahedron, more than sufficient. Oxygen is a supporter of combustion and seeing that 21% of the atmosphere are oxygen, it can be easy to see why it is the most common.

Upper Explosive Limits

An example of how necessary Oxygen is to a fire would be a room that is oversaturated with a flammable gas. If there is a gas leak, the room can get filled with the flammable gas and displace all oxygen from the room. That would mean that you could theoretically create a spark and nothing would happen, as there is no oxygen present to support the combustion. That level of saturation would be referred to being above the UEL (Upper Explosive Limit) of the flammable gas in question.


For an ignition, a fuel needs to be present. Fuel can take many shapes and does not refer to gasoline specifically. Fuel could be a solid, such as wood, a liquid, such as grease, a gas, such as propane or anything in between. A sufficient amount of fuel needs to be available to sustain the combustion process.

Lower Explosive Limit

To refer back to the flammable gas example, the LEL (Lower Explosive Limit) is the minimum amount of the gas required to become a fuel for the fire. Below that limit, the gas is not available in sufficient quantity, so once again a spark could NOT light a fire. The dangers for gases specifically are within the LEL and UEL. Fuels for fire are organized by their class and assigned a letter. That is how the correct extinguishing agent can be picked for the hazard.


The term heat refers to the fuel’s flashpoint, the lowest temperature at which the fuel will ignite. There is a surprisingly small amount of heat required to start a fire. The action of lighting a match creates enough heat through friction to support the combustion process and light the match. Heat can come from many sources, such as the sun or artificially created. Many extinguishing methods work by lowering the temperature of the fuel, one major reason why water is so effective.

Chemical Chain Reaction of the Fire

The fourth element, which moves the fire from the fire triangle, the conditions needed for ignition, to the tetrahedron, the sustained combustion, is the chemical chain reaction of the fire. The chemical chain reaction provides the necessary heat to sustain the combustion. So long as this heat is provided, the fire will continue to burn and grow. It will only stop when it is deprived of one or more sides of the fire triangle.

Extinguishing a Fire

As noted above, extinguishing a fire requires starving the fuel of one or more elements of the tetrahedron. Most standard extinguishing methods work on this principle. It is important to use the correct agent for the applicable fire. We have an overview here of the different classes of fires and their corresponding extinguishing agents. Water-based sprinkler systems and other suppression systems also work along the same principles.


Safety training can be very beneficial to most organizations. A team with knowledge about how fires start and how they can be prevented can protect your facility from a disaster. Nexus Fire & Safety offers comprehensive training programs for organizations. This includes fire warden training, extinguisher training, and custom programs for specialized facilities. We are ready to assist with any questions that you may have and offer 24-hour support to keep your safety systems in top shape!

How does a Fire Sprinkler work?

Multiple fire sprinkler heads, showing their shapes and sizes

Fire sprinklers are in many commercial and even some residential buildings. Most people know that a sprinkler going off means it’s a bad day and that hanging things off them is probably not the best idea. But how do fire sprinklers work? Does that red pull station by the door turn them on, and we shut them off when the fire is out? There are many misconceptions about fire sprinkler systems. We will provide an outline of the different types of sprinkler systems and how they work. For more detail, contact us, and our team of experts can assist with any questions you may have.

Types of Fire Sprinkler Systems

While the sprinkler heads may mostly look very similar, the system behind them can be quite different. There are four main types of systems, though they all are for the same purpose of putting fires out.

Wet Pipe Systems

Single sprinkler head with sensing element visible
Visible Sensing Element

This is the most common fire sprinkler system that everyone thinks of when they hear of fire sprinklers. All pipes in the system are filled with water and each sprinkler head has a sensing element (fusible link or glass bulb). Should the temperature get too hot at the ceiling, the sensing element will burst and allow for water to flow freely. As the system is filled with water there is minimal delay from activation to system flow. Wet pipe sprinkler systems are the most reliable and cost-effective, though they may not be appropriate for every application. As the water is under pressure in the pipes, the system cannot be subjected to freezing temperatures. Additionally, water can be quite harmful, which may not be appropriate for areas with sensitive equipment.

Dry Pipe Systems

Dry pipe systems are very similar to wet pipe systems. The major difference is that the pipes are filled with air instead of water. This allows for the system to be exposed to freezing temperatures, without any impact to its functionality. Dry systems can be found on patios and canopies, coolers and parking garages, amongst other places. The system is comprised of a specialty valve that keeps the water at bay with the assistance of the air pressure in the system. The sprinkler heads still have a sensing element and upon activation the air will escape. Once enough air has escaped, the valve will open and will release the water into the system and through the sprinkler head. As there is a delay upon activation of a dry pipe system, due to the time it takes to release all the air, the size of dry pipe systems is usually limited.

Preaction Systems

Preaction systems are more specialized systems. Their basic design is quite similar to a dry pipe sprinkler system, though the activation is what differs. Preaction systems are paired with electronic detection devices. A releasing panel is paired with these heat or smoke detectors and is connected to a specialized valve. The pipes of the system are still filled with air, just as they are in the dry pipe system. The sprinkler heads also still contain a sensing element.

There are three sub-types of preaction systems, depending on their activation:
  • Non-interlock system: the system will activate on the operation of detection devices OR if the sensing element of the sprinkler head bursts
  • Single interlock system: the system will ONLY activate on the operation of detection devices
  • Double interlock system: the system will activate if the detection devices AND the sensing element of the sprinkler head bursts.

Detection devices, such as heat detectors, usually have a lower threshold for activation of 135°F (65°C) vs. 165°F (74°C) for sprinkler heads. With a preaction system, multiple criteria can be required before the system will activate. That is the reason it is ideal for museums and other sensitive environments. As the double interlock system will significantly delay activation, with both criteria having to be fulfilled, the same size limits as a dry pipe system apply. Double interlock systems were initially designed for freezer storage warehouses. Areas, where the accidental presence of water can cause a significant amount of damage, are the best candidate for a double interlock.

Deluge Systems

Deluge sprinkler head showing lack of sensing element
Deluge Sprinkler Head Without Sensing Element

Deluge systems are very similar to preaction systems. The deluge system, however, does NOT have sensing elements in the sprinkler heads. That means upon water delivery, the water will flow from ALL sprinkler heads at once. Similar to a preaction system, an electronic means of detection will keep the valve closed. Upon activation of a smoke or heat detector, the system will start flowing water and all sprinkler heads will start releasing. This type of system is most suitable for high-hazard areas, such as power plants or aircraft hangars.

So, How Does a Sprinkler Work?

As you see with the examples above, there are a few different ways a sprinkler system can work. All activations of a sprinkler system are considered automatic, as they do not require any manual input. Most sprinkler systems will activate ONLY where it is necessary, which is usually only one or two sprinkler head locations. That is the reason sprinkler systems are so effective and yet are not as destructive as everyone might think. No matter the sprinkler, the principle is the same. Upon the presence of extreme heat from a fire, the system will activate and start spraying water. Water is one of the best ways to fight the fire, as it attacks the fire in several ways on the tetrahedron. Water cools, removes the heat component, and also removes the oxygen from the fire by displacing it.

Sprinkler System Service

While this article hopefully provided you with a basic outline of sprinkler systems, there are several other components to it. Our team can assist with the design, installation, inspections, and repair of any sprinkler system. We are ready to answer any questions you may have and are ready 24 hours a day, should you encounter any issues with your sprinkler systems.

What is a Backflow Preventer

Large Dual Check Valve Backflow Assembly

When we consume water from our tap, we automatically assume that it is safe for consumn. We expect the water to be clean and free of any pollutants or toxins. Backflow preventers play a considerable part in ensuring that is the case every time. To explain what a backflow preventer is, we first need to discuss what backflow is, when it comes to water.

Water in Buildings

When water enters any building, it is pressurized by the water purveyor (usually the city or county). This pressure ensures that when you turn on the tap, the water actually starts flowing. Without pressure, the water would never flow. Because we use water for significantly more than to drink it, there are many risks of pollutants or toxins contaminating the water. Manufacturing processes or additions of chemicals (fertilizer or pool chemicals, for example) can render the water harmful for human consumption.

As buildings use water differently, there could be a time when more water is requested than can be supplied initially. A famous example for this is a fire hydrant. The hydrant, when opened will create such a high flow rate, that it pulls water back out of buildings to service its consumption. That is where the danger comes in, as the potentially contaminated water is now pulled back into the water supply and could be distributed across the entire neighborhood. This event is called a cross-connection. As the city’s water supply is cross-connected with the potentially contaminated water within the building.

One of the first-ever documented cross connections, that caused a significant amount of harm happened in Chicago at the World’s Fair in 1933. This article discusses it in more detail: Chicago Backflow Incident. Another more recent incident happened in Pittsburgh, where two fire truck pumps overwhelmed the water supply and caused fire suppression foam to leak into the water system. More information here.

Where are Backflow Preventers usually installed?

Generally, backflow preventers can be found on the main incoming water line into the building. If the building has a sprinkler system, the very first component in the sprinkler system will be a backflow preventer. Backflow assemblies can be found in several locations throughout a building, Depending on the hazards that are present, individual water consumers may be protected by their own assembly. Some examples would be pools, ice machines, dishwashers, and other applications where water is mixed with chemicals. Backflow hazards range from minor to severe, depending on the effect the contaminated water can have on human health.

How does a backflow preventer work?

Backflow preventer assemblies are comprised of two one-way valves, referred to as check valves. These valves close when no water flow is present and thus restrict the reverse flow of the water. As there is two valves, there is a level of redundancy built into these devices. This redundancy ensures that the public water is still protected, even if one of the check valves has failed.

To learn more about backflow preventers, the American Water College has an excellent video demonstrating the functionality of a backflow preventer. Find it here.

There are several other components to a backflow preventer, such as the shut-off valves and test cocks, to provide a means of testing the assembly. There are two main backflow preventer types in use today, though there are about 15 different types altogether. The two most used are:

DCVA – Double Check Valve Assembly

  • The most common type of backflow prevention aseembly.
  • Suitable for minor-hazards. The American Water Works Association (AWWA) defines this hazard as a situation in which a cross-connection might create a nuisance or be aesthetically unpleasant but would NOT create a health hazard.  
  • The main parts of a DCVA are an inlet shutoff valve, two independently operating spring-loaded check valves (usually inside a single valve body), four test cocks, and an outlet shutoff valve. 

RPZ – Reduced Pressure Zones

  • More reliable than a DCVA, but also more elaborate.
  • Generally required for severe-hazard settings, defined by the AWWA as those in which an unprotected cross-connection could introduce substances capable of causing illness, death, or disease spread if introduced into the public water supply. 
  • Equipped with a relief valve in addition to two spring-loaded check valves. The relief valve will dump water in the event of a check valve failure, to ensure the water supply is protected.

Testing Requirements

Testing of backflow assemblies is generally required by the water authority. The American Water Works Association (AWWA) otulines the certification requirements for qualified technicians. Testing of an assembly is generally required every year, though some municipalities may require it more frequently. All testing needs to be completed by a qualified professional.

A backflow test involves a simulation of a backflow event with a specialized gauge under protected conditions. This will yield a test result indicating the functionality of the unit. If there is backflow, meaning water flowed back through the unit, it must be repaired or replaced immediately. Most backflow can be repaired, which involves gaskets and the check valves themselves. In some cases the entire backflow preventer may need to be replaced.

It is important to work with a qualified professional when it comes to backflow preventers. Incorrect installations or repairs can cause premature failures. Incorrect testing may also damage the units and without the necessary certifications, your water authority may reject the tests altogether. Regular testing of the backflow assemblies is crucial, as the liability for contaminating the water supply is ultimately your responsibility.

Nexus Fire & Safety can help you meet all your backflow testing requirements and offer the most cost-effective approach should one or more of your assemblies fail testing. Our technicians are fully certified and can assist with the design, installation, inspection and maintenance of all your fire safety systems, including backflow preventers. Get in touch today to learn more