Smoke Detectors, The case between Ionisation and Optical
Let’s start with a simple enough question. Are high performance optical detectors better than ionisation smoke detectors, particularly in data room and sensitive equipment applications? And the quick answer is that neither is always 100% better that the other when it comes to detecting all types of fire. Each type of sensor functions differently with the result that they respond differently to various fire conditions. While ionisation sensors will usually respond quicker to ‘flaming’ fires, optical sensors will almost certainly respond quicker to the ‘smouldering’ type of fires. So in the final analysis it would be wrong to say that one sensor type is better than the other as they both work effectively given the right circumstances.
Current standards for “fire suppression” systems dictate that two types of detector should be used in the sequence of activation. These are Ionisation smoke detection, traditionally used to sense the invisible early onset of a fire such as cable sheathing and over heating components and Optical smoke detection which is better suited to the more dense smoke produced in smouldering materials.
A combination of these two types is said to give a more balanced perspective of the early onset of fire with a minimum of two of each type installed on separate actuation zones of the protected risk.
Protecting the environment
Ionisation is the more sensitive of the two and will provide an earlier alarm to an impending fire condition. However there are environmental issues revolving around this type as a small radioactive source is used to produce the sensors ability to ionise air to differentiate between normal air and that laden with smoke particles. Whilst a single detector itself will not present a radiation problem, the world-wide cumulative amount for disposal is presenting a real issue and is one that needs to be addressed. As such, there are now schemes in force to reclaim detectors and dispose of the radioactive source in a more ethical manor.
Debate still rages as to the merits of Ionisation detectors with some detector manufacturers having ceased the production of this type of detector altogether. In their place they’ve developed sensors with a much wider and more sensitive optical range arguing that this development negates the need for having to opt for Ionisation detection. On the other hand, there are those who continue to maintain that even with optical advancement, an optical detector will never be as sensitive as a dedicated Ionisation head.
So, as reputable fire engineers and faced with these options, how do we decide between using or not using?
Not an easy question to answer as here at Nobel Fire Systems we can see the points raised in both arguments. However as an ethical and environmentally conscious company we would always prefer not to use Ionisation. Instead we recommend the use of multiple optical detectors from a manufacturer that has dedicated its research into a wide range optical sensor.
Our advice always is to ensure maximum protection is afforded to a risk. If a company is going to the length and expense of installing an “active” fire suppression system then it makes sense to offer the highest level of protection from day one.
High sensitivity smoke detection
Following the argument in favour of ionisation giving the earliest possible warning, then it makes more environmental sense to install high sensitivity smoke detection as the primary detection sensor, constantly sampling air from the risk. These types of detector with trade names such as VESDA and Strato give infinitely more sensitivity than standard conventional smoke detectors of ionisation or optical and can give the earliest warning available.
Let’s not also forget that the reduction of false alarms is an issue that needs addressing and industry knowledge points to the fact that ionisation detectors are more prone to give rise to a false alarm than their optical counterparts.
Commercial users certainly don’t want the inconvenience of attending a false alarm call from both an emotional and a potential cost point of view.
And the high incidence of unwanted alarms is causing the fire services to implement alarm management procedures in sites where there is an established track record of persistent false alarms. In the end analysis, this will only serve to have a substantial cost impact on those businesses involved.
The perfect package
When using high sensitivity smoke detection as the primary detection sensor, the detectors can be linked to the suppression system control panel and whilst not acting as part of the activation polling they can give an alarm local to the risk that will allow investigation by the owner at a stage that could allow early intervention and prevent a fire from escalating to the point of actuation.
So in conclusion, removal of the ionisation detector can be compensated for in a very effective and efficient fire suppression package which will provide freedom from false alarms, a better environment and importantly, a fire detection system that’s as good as it gets.