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Photoelectric Smoke Detectors

Are you indecisive on which smoke detector to go for? If yes, then this guide would be an inspiring read for you. We have written this guide on the photoelectric smoke detectors. In this guide, you’ll find all the information you need to know about the photoelectric smoke detector.

As you read through, be sure to take note of the main points. So it is expected that after reading through this guide, you should no longer have that indecision problem.

What Is a Smoke Detector

Smoke alarms are compulsory in most homes and units these days to ensure the safety of the occupants in the event of a fire.

A smoke detector is a device that senses the presence of smoke in a building and warns the occupants, enabling them to escape a fire before succumbing to smoke inhalation or burns. Equipping a home with at least one smoke detector cuts in half the chances that the residents will die in a fire

Two basic types of smoke detectors are currently manufactured for residential use. The photoelectric smoke detector uses an optical beam to search for a smoke. When smoke particles cloud the beam, a photoelectric cell senses the decrease in light intensity and triggers an alarm. This type of detector reacts most quickly to smoldering fires that release relatively large amounts of smoke.

Photoelectric Smoke Detectors

A photoelectric smoke detector is a light detector that uses a light beam and electrical photocells (photodiodes) to track smoke particles.

Photoelectric, or optical smoke detector, contains a source of infrared, visible, or ultraviolet light — typically an incandescent light bulb or light-emitting diode (LED) — a lens, and a photoelectric receiver — typically a photodiode. In spot-type detectors, all of these components are arranged inside a chamber where air, which may contain smoke from a nearby fire, flows.

In large open areas such as atria and auditoriums, optical beam or projected-beam smoke detectors are used instead of a chamber within the unit: a wall-mounted unit emits a beam of infrared or ultraviolet light which is either received and processed by a separate device or reflected the receiver by a reflector.

In some types, particularly optical beam types, the light emitted by the light source passes through the air being tested and reaches the photosensor. The received light intensity will be reduced due to scattering from particulates of smoke, air-borne dust, or other substances; the circuitry detects the light intensity and generates the alarm if it is below a specified threshold, potentially due to smoke.

Light beams (made of an incandescent bulb or infrared LED light that helps to collect the light source into a beam) in the smoke detector will reflect onto the photocells.

The photocells are arranged at a right-angle to the beam of light so that light entering the chamber does not typically attract the photocells.

This device aims a focused light source into a sensor chamber; when smoke enters the chamber, it reflects light, which then triggers the alarm. Photoelectric smoke detectors are best at detecting large smoke particles from slow, smoldering fires.

When smoke particles enter the optical chamber, these particles interfere with the light beam (i.e., the lights reflect off of the smoke particles) and then make contact with the electrical photocells. This contact increases the electrical charge in the detector to a threshold level, which initiates an alarm signal.

Photoelectric smoke detectors are typically installed in large commercial and social settings, including gymnasiums and auditoriums.

These detectors, according to several university studies, are significantly more effective in picking up smoldering fires. With today’s pervasive use of fire retardant materials, most fires actually smolder for a significant amount of time before growing into a flaming-fire.

The photoelectric smoke detectors are quicker activating with these smoldering fires and substantially the same in fast-burning fires. By utilizing a single sensor photo-electric smoke detector residents may be notified between 2 and 40 minutes earlier, based on university studies.

Photoelectric smoke alarms have a distinct advantage over the Ionisation version in that occupants are alerted quicker to smoldering smoke allowing time to escape from the premises. Most house fires start with a smoldering fire initially. Ionization alarms react when the house is well alight, significantly reducing the number of times occupants have to evacuate a burning home.

Advantages

  • Ideal for detecting dense smoke
  • Less prone to false alarms from cooking fumes or shower steam
  • Do not contain radioactive materials, making them safer for use
  • Suitable for general use
  • Good for smoldering fires and dense smoke
  • Not as prone to cooking nuisance alarms

Disadvantages

  • Sensitive to dust particles and insects, meaning that regular maintenance is needed
  • More expensive
  • Expensive to maintain
  • Require more current to operate (they are typically wired to a 110-volt power source)

The light beam in a typical photoelectric smoke detector can be obscured in two ways:

  • The light-obscuring method

Dense smoke tends to only obscure part of the light beam, whereas less-dense smoke particles can move around more freely, obscuring more of the light beam and therefore, impacting the alarm system. In some instances, a mirror is used to position the light beam to measure the area of coverage of the smoke particles.

  • The light-scattering principle

A light scattering principle is based on the idea that smoke particles entering the sensing chamber strike the light beam and scatter the light onto photoelectric particles.

When Is a Photoelectric Smoke Detector Best?

Photoelectric smoke alarms respond fastest to smoldering fires that begin slowly and burn without a flame for a long period of time. It’s no secret that many deaths from residential fires occur as a result of smoke inhalation rather than flames.

Being able to detect smoke early can be a lifesaver, helping families to escape before the flames have even started and before potentially life-threatening smoke inhalation. These types of fires often occur when small flames from things like candles or cigarettes are left unattended. The Cause fewer false alarms from cooking in the kitchen or steam in bathrooms, and they do not contain radioactive material.

How Do Photoelectric Smoke Detectors Compare To Other Smoke Detectors?

Other popular technologies for smoke detectors are ionization alarms and dual-sensor smoke detectors. The dual-sensor smoke detector has both ionization and photoelectric technology inside. Ionization smoke alarms are best for detecting rapid flame fires, while photoelectric smoke alarms protect against slower, smoldering fires.

Should I Have A Photoelectric Smoke Detector?

It’s safe to say every home should have a photoelectric smoke detector. While the ionization smoke detector has been proven more effective in detecting flaming fires, photoelectric alarms outperform them when it is a smoldering fire. For best protection, it is recommended to have both types of fire alarms throughout your home.

The upside is that there will be less risk of false alarms since they have a higher threshold of smoke tolerance. The downside is that in certain situations like flaming fires that do not produce large smoke particles, by the time it sounds the alarm, the fire may have grown too large to be easily tackled.

If you’re looking for an optical smoke detector, get one with as many of these features as possible:

  • Bright strobe escape lights – During an actual fire, visibility is extremely poor so these lights are useful.
  • Remote controllable mute button to silence the alarm in case of false alarms.
  • Lithium battery operated. Lithium batteries can last 10-15 years without changing.
  • Secure battery compartments with auto-lock to prevent children tampering with them.
  • Alarm notification in case the batteries need changing.

What’s inside the detector?

Once Freymann and Tolman had discovered their fiber, it was relatively simple to build a part-electrical, part-mechanical smoke detector around it:

  • A length of the magic fiber (yellow) is stretched around a wheel (red) inside a metal container (gray) with holes at the bottom through which smoke can enter.
  • The fiber is attached to a pivoting lever (light blue), held in place by a spring (purple).
  • The blue lever holds another pivoting lever (green) in place.
  • The green lever supports an electrical contact (dark blue) and holds it well above a second identical contact.
  • The two contacts connect to a battery-powered bell or another electrical alarm circuit.

You can create the safest environment possible for your family by installing a mix of photoelectric and ionization smoke detectors. It’s too risky to go with one and not the other because there is no way to predict what type of fire threat your home may experience.

Some smoke detectors utilize both ionization and photoelectric technologies. These types of smoke detectors are known as “dual” smoke detectors and are widely available at home improvement stores and online at a variety of price points and from several brands.

As a homeowner, you want to do all you can to take advantage of the potentially lifesaving technology available for smoke and fire detection. No matter the type of smoke detector you select, it’s crucial that you test your detector, routinely.

CONCLUSION

In summary, it must be stressed that, despite the functional differences and levels of sensitivity between photoelectric and ionizing smoke detectors, both devices are acceptable as life-saving smoke sensors.