Modern petrochemical plants are always at the risk of fire since lot of toxin inflammable gases are often present, the temperature is also high . These are normally ums class
(unmanned machionery space). Supervisory rooms are always away from the actual plant. All light fixures are explosion proof.Little spark can cause great fire. Normal fire sensors can not be used. Special designed sensors are used. In case smoke enters into the sensor & sensor get activated ,
The following action will take place
Features:
1) Sounds an fire alarm to attract attention .
2) If the reset SW is not pressed within 30 seconds, the projects takes further action,
3) Shut down the plant,
4) Start sprinkling,and
5) Make an emergency call to , deliver an emergency message .
6) It will call five times at the interval of one minute and again check for the smoke, if smoke is still present it will continue to do so otherwise start monitoring again.

CIRCUIT EXPLANATION:
This project is based on 8051 microcontroller.(IC2)
IC3 is 74245 and is used as buffer.
IC4 P89021 is a one time programmable(otp) chip where messages are stored. This is 21 second speech ic where total of 12 messages can be recorded on eight different locations, but total duration should not be more than 21 seconds. recorded messages can be played back by setting the trigger pin 10 & 11 high, making these pin low will stop the message, Setting these pin high will repeatedly replay the same message.

Ic Lm 386(IC5) is an audio amplifire . Audio output from speech IC4 pin 7 cout is coupled to this ic on pin 3 through VR2 volume control and C10. Amplified output from pin 5 drives the speaker through capacitor C14. R14 and C13 are for tone correction.