AS1851:2012 - Smoke Detector Sensitivity Testing

A smoke detector is a sensitive device designed to detect a fire from the by-products of combustion. You can read more about the operation of fire detection and alarm systems and smoke detectors in our popular series of articles titled "Principles of Fire Safety".

Earlier today I received an email from CW (alias) who asked the question "what are the requirements for testing the sensitivity of collective smoke detectors in accordance with Australian Standard AS1851:2012?"

From: CW
Date: Fri, May 31, 2013
Subject: Detector sensitivity testing

G’day Russ

I had a call today asking about the requirements in AS1851-2012 Appendix G6 to test the sensitivity of a conventional smoke detector. Specifically he wanted to know how the activity can be performed as he is struggling to locate the required test equipment and the availability of manufacturers data, particularly where the detectors are more than 10 years old.

Can you provide any supporting information that would assist with the application of this particular clause.

FYI, the member didn’t attend the recent Fire Detection Seminar where this information was covered.

Cheers,

Chris

Australian Standard AS1851:2012 has taken a different approach to previous editions of the Standard, outlining the requirements for a "functional test" and a "sensitivity test". While both of these requirements have existed in the previous edition of the Standard, they have been expanded on in the 2012 edition.

Functional Test

A functional test (also known as the go/no-go test) is a simple test of a detector to determine if it will operate given the correct stimulus. For example being exposed to the sufficient quantity and duration of heat or smoke or flame or carbon monoxide.

In addition, this test may also used to verify the operation of associated ancillary control facilities as part of the end-to-end test defined in the Standard.

The Standard provides guidance on the functional test of each of the following types of fire detector;

  • G2 - Point Type Heat Detector Functional Test
  • G3 - Liner Heat Detector Functional Test
  • G4 - Point Type Smoke Detector Functional Test
  • G8 - Beam Type Smoke Detector Functional Test
  • G11 - Flame Detector Functional Test

Sensitivity Test

Interestingly, the sensitivity test was introduced into the 2005 edition of the Standard to identify detectors that may be more sensitive that their approved design.

The reason this test is done is to help eliminate or reduce the incidence of nuisance alarms because a detector is too sensitive.

Appendix G "Fire Detector Testing" provides more information about the sensitivity testing requirements of the the 2012 edition of the Standard for the following types of fire detectors, and their variations;

  • G5 - Point Type Smoke Detector Sensitivity
  • G6 - Point Type Smoke Detector In Situ Sensitivity Test
  • G7 - Smoke Detectors capable of reporting 'out of sensitivity range'
  • G10 - Aspirating Smoke Detector Sensitivity Test
  • G12 - Flame Detector Sensitivity Test
  • G14 - CO Fire Detector Sensitivity Test

In the drafting process of this Standard sensitivity testing was the subject of a lot of discussion lasting alost 9 months from early 2010 to late 2010. During that time there were a number of iterations of Appendix G.

The process of community review also introduced further discussion about the intent and wording of these requirements.

What the Standards writers (of which I was one of the contributors) were trying to achieve was to document methodologies that could be applied irrespective of the technology that supported the operation of the detector.

The most difficult of these were smoke detectors as there are a multitude of technologies and algorithms built into a detector and fire alarm panels designed to overcome deceptive phenomena. Some of these technologies can be used determine the level of sensitivity or contamination of a detector from the control panel.

There are essential three methods of communication with fire detectors, these include;

  • collective (also known as conventional);
  • analogue;
  • wireless.

In each case there may also be variations (depending on the manufacturer) on the features of each of these three detector types. I have also listed three primary features of moden smoke detectors that include;

  • individual detector identification;
  • detector sensitivity tracking;
  • algorithms to overcome deceptive phenomena.

Over time, smoke detectors are likely to become more sensitive (i used to think they would become less sensitive) and manufacturers designed features to overcome the result - false alarms. Each manufacturer has their own terms and phrases to describe these features, such as 'drift compensation', 'intelligent', 'neural network' and others.

The reality is that these features also introduce complexity into the way detectors operate and need to be maintained.

The AS1851:2012 edition of the Standard considers these variations and provides three methods to verify the sensitivity of "Point Type Smoke Detectors";

Smoke Detectors capable of reporting 'out of sensitivity range'

These types of smoke detectors are often called 'addressable' or 'analogue addressable' and have the ability of recording and transmitting the level of contamination of the detector back to a control panel. Typically accessing the level of contamination of each smoke detector can be done from the liquid crystal display (LCD) or a laptop plugged into the fire panel.

There are also some manufacturers who can provide a handheld device that can also read the level of contamination of a detector in the field.

Point Type Smoke Detector In Situ Sensitivity Test

Where a smoke detector is not capable of reporting its 'out of sensitivity range' then each detector shall be tested on the 10th anniversary of being installed using a test device designed for the purpose of verifying the sensitivity of the detector.

This is the same test as was previously established in the the 2005 edition of the Standard.

Lastly where the sensitivity of a point type smoke detector cannot be tested or verified, the detector shall be replaced with a new or 'cleaned and recallibrated' unit of equivalent type, followed by a functional test.

Summary

Smoke detectors are sensitive devices designed to detect the by-products of combustion (smoke). Over time they become contaminated by airborne particles and may also become more sensitive.

Fire detector sensitivity testing is required to be completed in Australian Standard AS1851:2005 and AS1851:2012 in order to identify detectors that are are likely to cause nuisance alarms or fail to operate in accordance with their intended design.

There are two primary ways to test and verify the sensitivity of a smoke detector;

  1. from a control panel or handheld device designed for the purpose; or
  2. using a test tool designed for the purpose.

Where the sensitivity of a smoke detector cannot be tested and verified, it must be replaced with a new unit or a 'cleaned and recalibrated' unit.

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