Q: How Do Photoelectric Smoke Detectors Work?

A: All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up. Smoke detectors can run off of a 9-volt battery or 120-volt house current.

Occasionally you will walk into a store and a bell will go off as you cross the threshold. If you look, you will often notice that a photo beam detector is being used. Near the door on one side of the store is a light (either a white light and a lens or a low-power laser), and on the other side is a photo detector that can "see" the light.

When you cross the beam of light, you block it. The photo detector senses the lack of light and triggers a bell. You can imagine how this same type of sensor could act as a smoke detector. If it ever got smoky enough in the store to block the light beam sufficiently, the bell would go off. But there are two problems here: 1) It's a pretty big smoke detector, and 2) it is not very sensitive. There would have to be a LOT of smoke before the alarm would go off -- the smoke would have to be thick enough to completely block out the light. It takes quite a bit of smoke to do that.

Photoelectric smoke detectors therefore use light in a different way. Inside the smoke detector, there is a light and a sensor, but they are positioned at 90-degree angles to one another, like this:

In the normal case, the light from the light source on the left shoots straight across and misses the sensor. When smoke enters the chamber, however, the smoke particles scatter the light and some amount of light hits the sensor. The sensor then sets off the horn in the smoke detector. Photoelectric detectors are better at sensing smoky fires, such as a smoldering mattress.

Contact ABCO Fire today for all of your fire equipment needs. We want to be your source for fire extinguishers, fire alarms, fire sprinklers and more.

Established in 1975, ABCO supplies fire protection and prevention needs for nearly 50,000 customers in the manufacturing, retail, government, and marine industries. They provide portable and fixed systems and complement these products with inspection, maintenance, and certification services. Their list of products include fire extinguishers, kitchen equipment, fire suppression systems, alarm & detection systems, first aid & safety equipment, exit & emergency lighting, and power washing equipment. ABCO offers extensive repair and cleaning services for kitchen exhaust systems and hoods including power washing.

Q: How do multi-class dry chemical fire extinguishers work?

A: If you ask any firefighter what it takes to create a fire, you will learn that you have to have three things:

  1. A fuel - some sort of combustible solid, liquid or gas
  2. Oxygen to react with the fuel
  3. Heat - there must be enough heat to get the fuel above its flash point. There is paper on your desk right now that is surrounded by oxygen. It does not burn unless you get the paper hot enough.

If you want to put out a fire, you need to remove one of the three elements. When you watch firefighters battling a forest fire, they generally try to remove fuel or heat. Either they pour water on the fire to reduce the temperature, or they try to bulldoze strips of bare earth to eliminate the fuel.

A carbon dioxide fire extinguisher works by eliminating oxygen and replacing it with carbon dioxide. You could do the same thing with just about any non-oxidizing gas (nitrogen, for example), but carbon dioxide is inexpensive and easy to store.

Another way to cut off oxygen is to throw a blanket over the fire. Covering the fire with dirt or sand does the same thing. You might have heard that you can put out a kitchen fire by throwing baking soda or salt on the fire. Throwing sand would do the same thing, but most people have more salt in their kitchens than they have sand.

Dry chemical fire extinguishers are by far the most common fire extinguishers in the home. They can handle all three types of fires you would find in a kitchen or workshop: combustible solids like wood or paper, combustible liquids like gasoline or grease, and electrical fires. The idea behind a dry chemical fire extinguisher is to blanket the fuel with an inert solid (similar to dirt or sand). A dry chemical extinguisher sprays a very fine power of sodium bicarbonate (normal baking soda), potassium bicarbonate (nearly identical to baking soda), or monoammonium phosphate. These solids coat the fuel and smother the fire.

Established in 1975, ABCO supplies fire protection and prevention needs for nearly 50,000 customers in the manufacturing, retail, government, and marine industries. They provide portable and fixed systems and compliment these products with inspection, maintenance, and certification services. Their list of products include: fire extinguishers, kitchen equipment, fire suppression systems, alarm & detection systems, first aid & safety equipment, exit & emergency lighting, and power washing equipment. ABCO offers extensive repair and cleaning services for kitchen exhaust systems and hoods including power washing.

Q: Why does smoke come from a fire?

A: Let's say you have a nice fire going, and it has burned down to the point where what you see is a collection of hot "glowing embers." The fire is still producing a lot of heat, but it is producing no smoke at all. You might have gotten to this point either by starting with logs in a fireplace or by starting with charcoal. If you now toss a piece of wood, or even a sheet of paper, onto this fire, what you will notice is that the new fuel produces a lot of smoke as it heats up. Then, all of a sudden (often with a small pop), it bursts into flame and the smoke disappears. If you have a fireplace or wood stove or if you have been around a lot of campfires, this little scene is very familiar to you. It tells you a lot about smoke—let’s look at what is happening.

There are four things that you find in any piece of wood

  1. Water - Freshly cut wood contains a lot of water (sometimes more than half of its weight is water). Seasoned wood (wood that has been allowed to sit for a year or two) or kiln-dried wood contains a lot less water, but it still contains some.
  2. Volatile organic compounds - When the tree was alive, it contained sap and a wide variety of volatile hydrocarbons in its cells. Cellulose (a chief component of wood) is a carbohydrate, meaning it is made of glucose. A compound is "volatile" if it evaporates when heated. These compounds are all combustible (gasoline and alcohol are, after all, hydrocarbons -- the volatile hydrocarbons in wood burn the same way).
  3. Carbon
  4. Ash - Ash is the non-burnable minerals in the tree's cells such as calcium, potassium, and magnesium.

Established in 1975, ABCO supplies fire protection and prevention needs for nearly 50,000 customers in the manufacturing, retail, government, and marine industries. They provide portable and fixed systems and compliment these products with inspection, maintenance, and certification services. Their list of products include: fire extinguishers, kitchen equipment, fire suppression systems, alarm & detection systems, first aid & safety equipment, exit & emergency lighting, and power washing equipment. ABCO offers extensive repair and cleaning services for kitchen exhaust systems and hoods including power washing.

How Do Ionization Smoke Detectors Work?

All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up. Smoke detectors can run off of a 9-volt battery or 120-volt house current.

Ionization smoke detectors use an ionization chamber and a source of ionizing radiation to detect smoke. This type of smoke detector is more common because it is inexpensive and better at detecting the smaller amounts of smoke produced by flaming fires. Inside any ionization detector is a small amount (perhaps 1/5000th of a gram) of americium-241. The radioactive element americium has a half-life of 432 years, and is a good source of alpha particles.

An ionization chamber is very simple. It consists of two plates with a voltage across them, along with a radioactive source of ionizing radiation, like this: The alpha particles generated by the americium have the following property: They ionize the oxygen and nitrogen atoms of the air in the chamber. To "ionize" means to "knock an electron off of." When you knock an electron off of an atom, you end up with a free electron (with a negative charge) and an atom missing one electron (with a positive charge). The negative electron is attracted to the plate with a positive voltage, and the positive atom is attracted to the plate with a negative voltage (opposites attract, just like with magnets). The electronics in the smoke detector sense the small amount of electrical current that these electrons and ions moving toward the plates represent.

When smoke enters the ionization chamber, it disrupts this current -- the smoke particles attach to the ions and neutralize them. The smoke detector senses the drop in current between the plates and sets off the horn.

Speaking of alarms, whenever the words "nuclear radiation" are used, an alarm goes off in many people's minds. The amount of radiation in a smoke detector is extremely small. It is also predominantly alpha radiation. Alpha radiation cannot penetrate a sheet of paper, and it is blocked by several centimeters of air. The americium in the smoke detector could only pose a danger if you were to inhale it. Therefore, you do not want to be playing with the americium in a smoke detector, poking at it, or disturbing it in any way, because you don't want it to become airborne.

Established in 1975, ABCO Fire supplies fire protection and prevention needs for nearly 50,000 customers in the manufacturing, retail, government, and marine industries. They provide portable and fixed systems and compliment these products with inspection, maintenance, and certification services. Their list of products include: fire extinguishers, kitchen equipment, fire suppression systems, alarm & detection systems, first aid & safety equipment, exit & emergency lighting, and power washing equipment. ABCO offers extensive repair and cleaning services for kitchen exhaust systems and hoods including power washing.

Hazards Posed by Wood-Fired Cooking

Want to win a free steak dinner? To promote their new “Wood-Fired Grill”, a major restaurant chain was recently dishing out free meals to customers with “Wood” or “Fire” in their name. Wood-fired cooking, however, needs little promotion right now with diners craving the rustic sights, scents, and flavors of foods prepared over a hardwood flame. Unfortunately, this type of cooking comes with additional fire hazards not seen in more conventional methods of commercial food preparation.

Last month, Retail & Restaurant Facility Business invited ABCO’s Alex Garrote to share his thoughts on the hazards posed by wood-fired cooking, and how those hazards should be addressed. From restaurant roof fires started by floating embers, to methods of handling a fuel source that can be difficult to extinguish, his article offers some insights every prospective wood-fired chef should think about.

If you are considering adding a wood-fired appliance to your commercial cooking operation, contact ABCO Fire early in the process to ensure the new hazard is properly protected. Contact our Restaurant Installation Department at 800-875-7200 for more information.

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