FAQ Orals (Fire Detection)

What Is The Principle Operation Of A Flame Detector? 
As Flame Has A Characteristic Flicker Frequency Of 25Hz, Use Is Made Of This Fact To Trigger An Alarm.  Flickering Radiation From Flames Reaching The Detector Lens/filter Unit, Which Only Allows Infra-red Rays To Pass And Be Focused Upon The Cell.  The Signal From The Cell Goes Into The Selective Amplifier, Which Is Tuned To 25Hz, Then To A Time Delay Unit (to Minimise Incidence Of False Alarms) Then To An Alarm Circuit.
 
What Is The Principle Operation Of A Heat Detector?
This Type Of Heat Detector Uses Two Bi-metalic  Strips/coils Attached To A Vertical Support Bracket.  When Temperature Is Present, The Bi-metalic Strips Will Start To Move, At A Fixed Temperature The First Strip Will Hit A Stop, The Second Strip Continuing To Move, Thus The Contact Is Made And Triggers The Alarm.
.
What Is The Principle Operation Of A Smoke Detector?
The Above Detector, Of The Light Scatter Type Uses A Photo Cell Separated By A Barrier From A Semi-conductor Intermittently Flashing Light Source Housed In An Enclosure Whose Containment Allows Smoke But Not Light Inside.  When Smoke Is Present In The Enclosure, Light Is Scattered Around The Barrier On The Photocell And An Alarm Is Triggered.
 
Once A Fire Detector Has Detected Or Sensed A Fire, What Happens?
Associated With Fire Detectors Is A Circuit Connected To An Alarm Panel, Which Is Usually Situated On The Bridge, Where The Alarm Is Accepted, Usually There Is A Repeater Panel In The Engine Control Room.  The Panel Giving An Indication On Which Deck And Zone The Detector Was Activated.  Someone Will Then Be Sent To Investigate And Verify If It Is A Fire Or A False Alarm.
 
Where Would You Find Heat Detectors And Why?
Heat Type Fire Detectors Would Be Used In Places Such As The Galley, Where Other Types Of Detectors Would Give False Alarms.
 
What Type Of Detector Should Be Fitted In Conjunction With An Infra-Red Type Fire Detector?
It Should Be Used In Conjunction With A Smoke Detector, To Give An Early Warning Of Fire.