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Questions and Answers
What is the primary function of intrinsic safety?
What is the primary function of intrinsic safety?
Which class of hazardous environments includes flammable gases and vapors?
Which class of hazardous environments includes flammable gases and vapors?
What is a key design principle for intrinsically safe circuits?
What is a key design principle for intrinsically safe circuits?
Which of the following materials is classified under Class 2 hazardous environments?
Which of the following materials is classified under Class 2 hazardous environments?
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What role do current-limiting devices play in intrinsic safety?
What role do current-limiting devices play in intrinsic safety?
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What is the function of barriers in intrinsically safe circuits?
What is the function of barriers in intrinsically safe circuits?
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Which component is essential for the functionality of an optic isolator?
Which component is essential for the functionality of an optic isolator?
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In the photo eye scenario on a conveyor, what type of environment is classified?
In the photo eye scenario on a conveyor, what type of environment is classified?
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What is an essential requirement for maintaining safety in intrinsically safe environments?
What is an essential requirement for maintaining safety in intrinsically safe environments?
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What does the light-sensitive transistor do in an optical isolator's operation?
What does the light-sensitive transistor do in an optical isolator's operation?
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Study Notes
What is Intrinsic Safety?
- A way to minimize fire and explosion risks in hazardous environments
- Prevents sparks and heat sources by limiting current flow
- Essential for environments where flammable materials may be present
Why is Intrinsic Safety Important?
- Helps prevent fires and explosions caused by electrical issues in hazardous environments
- Minimizes risks to personnel and equipment
Types of Hazardous Environments
- Class 1: Flammable gases and vapors (e.g., gasoline, hydrogen, natural gas, propane, ethanol, methane)
- Class 2: Combustible dusts (e.g., metal and metal alloys, charcoal, carbon black, flour, plastics, grains, wood)
- Class 3: Flying objects or fibers (not covered in this video)
UL Standard for Intrinsic Safety
- Class 1: Environments with flammable gases and vapors
- Class 2: Environments with combustible dusts
- Class 3: Environments with flying objects or fibers (not covered in this video)
Designing Intrinsically Safe Circuits
- Optic Isolation: Uses light to transmit signals between circuits, preventing electrical flow.
- Barriers: Devices that isolate sensors from electrical cabinets
- Current-Limiting Devices: Limit current flow to safe levels
Understanding Optic Isolators
- Optical isolation is used to isolate circuits and prevent electrical flow between different voltage levels.
- Components: Diode and a light-sensitive transistor.
- Functionality: Current through diode illuminates transistor, enabling current flow through collector and emitter.
Example of Intrinsic Safety in Automation: Photo Eye on a Conveyor
- Scenario: Photo eye on a conveyor in a plant with dust ignition hazard.
- Risk Assessment: Environment classified as Class 2, Division 2 (hazardous atmosphere under normal conditions).
- Solution: Using an intrinsically safe barrier to isolate the photo eye from the electrical panel.
- Barrier Functionality: Normally open, toggled on by a bag of flower. Photo eye turns on diode in barrier causing transistor to activate and signal PLC.
- Important Considerations: Not all photo eyes are compatible with intrinsically safe barriers, follow manufacturer's guidelines for wiring.
Essential Requirements for Intrinsically Safe Environments
- Pressurized Enclosures: Compressed air used to create positive pressure in panels to prevent dust entry.
- Sealing: Panels are sealed with putty or sealant to maintain pressure.
- Pressure Switches: Activate a red strobe light when panel is opened, indicating unsafe conditions.
Class 2, Division 1 Requirements
- Requires pressure switches for loss of pressure and disconnects line power to all panels in the area when unsafe.
- Keyed Bypass Switch: Allows temporary power during maintenance, but activates a red strobe light when the panel is opened.
Example: Load Cell on a Checkweigher Conveyor
- Scenario: Checkweigher conveyor requires an intrinsically safe barrier to limit voltage and current of the load cell.
- Important Consideration: Select a load cell compatible with the intrinsically safe barrier.
Intrinsic Safety
- Designed to minimize fire and explosion risks in hazardous environments
- Achieved by limiting current flow, preventing sparks and heat sources
- Essential for areas containing flammable materials
Importance of Intrinsic Safety
- Prevents fires and explosions caused by electrical issues
- Minimizes risks to personnel and equipment
Hazardous Environments
- Class 1: Flammable gases and vapors (e.g., gasoline, hydrogen, natural gas, propane, ethanol, methane)
- Class 2: Combustible dusts (e.g., metal and metal alloys, charcoal, carbon black, flour, plastics, grains, wood)
- Class 3: Flying objects or fibers (not covered in this video)
UL Standard for Intrinsic Safety
- Class 1: Environments with flammable gases and vapors
- Class 2: Environments with combustible dusts
- Class 3: Environments with flying objects or fibers (not covered in this video)
Designing Intrinsically Safe Circuits
- Optic Isolation: Uses light to transmit signals between circuits, preventing electrical flow.
- Barriers: Isolate sensors from electrical cabinets.
- Current-Limiting Devices: Limit current flow to safe levels
Optic Isolators
- Isolates circuits and prevents electrical flow between voltage levels
- Components: Diode and light-sensitive transistor
- Functionality: Current through diode illuminates transistor, allowing current through collector and emitter.
Automation Example: Photo Eye on a Conveyor
- Scenario: Photo eye on a conveyor in a dust ignition-hazardous plant
- Risk Assessment: Environment classified as Class 2, Division 2 (hazardous atmosphere under normal conditions)
- Solution: An intrinsically safe barrier isolates the photo eye from the electrical panel
- Barrier Functionality: Normally open, activated by a bag of flour. Photo eye turns on diode in barrier, activating transistor and signaling PLC
- Important Considerations: Not all photo eyes are compatible with intrinsically safe barriers, consult manufacturer guidelines for wiring.
Intrinsically Safe Environment Requirements
- Pressurized Enclosures: Compressed air maintains positive pressure in panels to prevent dust entry
- Sealing: Panels are sealed with putty or sealant to maintain pressure
- Pressure Switches: Activate a red strobe light when the panel is opened, indicating unsafe conditions
Class 2, Division 1 Requirements
- Requires pressure switches for loss of pressure and disconnects line power to all panels in the area when unsafe
- Keyed Bypass Switch: Allows temporary power during maintenance, but activates a red strobe light when the panel is opened
Example: Load Cell on a Checkweigher Conveyor
- Scenario: Checkweigher conveyor requires an intrinsically safe barrier to limit voltage and current of the load cell
- Important Consideration: Select a load cell compatible with the intrinsically safe barrier.
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Description
This quiz explores the concept of intrinsic safety and its importance in preventing fire and explosion risks in hazardous environments. It covers different classifications of hazardous environments and the UL standards related to intrinsic safety. Test your knowledge on how to design safe systems in environments where flammable materials may be present.
