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Flammable Liquids and Safety Measures
Managing hazardous electrical areas requires a thorough understanding of the risks involved and the implementation of stringent safety measures. Electrical systems situated in environments where flammable gases, or vapors, are present face unique challenges that necessitate careful planning and compliance with specific guidelines to prevent accidents and ensure operational safety.
Understanding hazardous areas involves recognizing the potential dangers associated with electrical equipment in these environments. Concerns arise from the possibility of sparks or heat generated by electrical equipment, which can ignite flammable substances and lead to dangerous explosions or fires. Addressing these risks requires a clear grasp of hazardous area classifications and legal requirements to ensure all safety protocols are adhered to.
In this blog post, we will provide a detailed examination of various aspects of hazardous electrical areas. Here’s a breakdown of what you’ll find:
What are Hazardous Electrical Areas
Hazardous electrical areas are environments where electrical equipment is used in the presence of flammable gases, or vapors, posing significant risks of fire or explosion. The primary concern is that sparks or heat generated by electrical equipment can ignite these flammable substances, leading to dangerous incidents. Proper management of these areas involves understanding hazardous area classifications, implementing stringent safety measures, and complying with legal regulations to ensure safe operation and prevent accidents. Effective safety protocols and specialized equipment are crucial to mitigating the risks associated with hazardous electrical areas.
Why Are There Concerns with Electrical Equipment?
When thinking about Area Classification, the first question that comes to mind is: Why are there concerns with electrical equipment?
- Arcs and Sparks Occur in Normal Operation: Electrical equipment often produce arcs and sparks during their regular functioning, such as when switches are operated or connections are made or broken. These arcs and sparks can ignite flammable gases in hazardous environments, posing a significant risk of explosion or fire.
- Consumption of Energy Produces Hot Surfaces: Electrical devices consume energy, and this process generates heat. Over time, components like resistors, transformers, and motors can become very hot. In hazardous areas, these hot surfaces can ignite flammable materials, creating a potential hazard.
- Malfunction Creates More Potential Ignition Sources: When electrical equipment malfunctions, it can produce additional sources of ignition, such as overheating, short circuits, or electrical arcing. These malfunctions increase the risk of fire or explosion, especially in environments where flammable substances are present.
- Sometimes Connecting Circuits of Components – results in an ignition risk. The use of Intrinsically Safe Equipment can minimize such risks. Intrinsically safe equipment is designed to operate safely in hazardous areas by ensuring that the electrical energy available in the circuit is not sufficient enough to cause ignition. This design consideration is crucial for minimizing the risk of ignition in dangerous environments.
- Electrical Equipment Must Be Selected and Installed Carefully to Ensure There Is Minimal Risk of Ignition: Choosing and installing electrical equipment for use in hazardous areas requires careful consideration of the potential risks. Equipment must be suitable for the specific conditions and comply with safety standards to prevent accidental ignition of flammable substances.
- Hazardous Area Classification (HAC) Was Developed as a Means to Identify Hazardous Areas and Determine Equipment Selection: To manage the risks associated with electrical equipment in hazardous areas, a system of area classifications were developed. This system categorizes different Classes and Divisions based on the potential for the presence and concentration of flammable gases, vapors, or dust. Proper classification helps in selecting the appropriate equipment and safety measures for each zone, ensuring a safer working environment.
Hazardous Area [Electrical] Classification
The purpose of Hazardous Area [Electrical] Classification (HAC) is to minimize the likelihood that ignition sources associated with electrical equipment could be present in areas where spills or releases of flammable or combustible materials could occur. To prevent fire and ignition in an industrial setting, it’s crucial to manage ignition sources. You already have the potential for fuel and oxygen (or an explosive atmosphere) in the process environment, so minimizing ignition sources related to electrical equipment is essential.
Typical sources of sparking and hot surfaces include:
- Motors for pumps, agitators, and mixers
- Fans and blowers
- Plug-in equipment and receptacles
- Powered instrumentation
- Switchgear and relays
- Communications equipment
Hazardous Area Classification also provides guidance on areas where other types of ignition sources should be excluded.
Legal Considerations
National Electrical Code® (NEC®)/NFPA 70, Articles 500 -502:
These articles contain guidelines specifying area classifications for flammable gases, flammable and combustible liquids, dusts, and fibers. They determine the type and design of equipment and wiring methods permitted in classified areas.
OSHA – General requirements
Hazardous (classified) locations – 29CFR Part 1910.307
“Scope. This section covers the requirements for electric equipment and wiring in locations which are classified depending on the properties of the flammable vapors, liquids or gases, or combustible dusts or fibers which may be present therein and the likelihood that a flammable or combustible concentration or quantity is present. Each room, section or area shall be considered individually in determining its classification.”
National Fire Protection Association
- All NFPA Standards that Cover Gases, Vapors, and Dusts contain Sections that address the need for Hazardous Area (Electrical) Classification
- NFPA 497 (2021) Recommended Practice for the Classification of Flammable Liquids, Gases or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
- NFPA 499 (2021) Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
National Fire Protection Association
- All NFPA Standards that Cover Gases, Vapors, and Dusts contain Sections that address the need for Hazardous Area (Electrical) Classification
- NFPA 497 (2021) Recommended Practice for the Classification of Flammable Liquids, Gases or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
- NFPA 499 (2021) Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
Fire Triangle: Liquid and Gases
- Fuel: This can be natural gas, toluene, or any other combustible or flammable liquid present in your area.
- Oxidant: Typically, this is the oxygen in the air.
- Ignition Source: Any energy source capable of initiating combustion.
For liquids, it’s important to know the flashpoint. If the liquid’s temperature is above its flashpoint, it can produce vapors that may ignite. Additionally, we need to know the flammability limits of the material to determine if the released gas or vapor concentration is within these limits. If sufficient oxygen is present (which it typically is unless excluded by using nitrogen, argon, or carbon dioxide), there is a risk of combustion.
For liquids:
- Liquid Temperature Above Its Flash Point: If the temperature of the liquid is above its flash point, it can produce vapors that may ignite.
- Concentration Within Flammable Limits: The concentration of the gas or vapor must be within flammable limits to pose a risk.
- Sufficient Oxidant: Typically, oxygen must be present in adequate amounts.
- Energetic Ignition Source: An ignition source must be present to start the combustion process
Classification of Liquids - Flammable (Ref. NFPA 30)
Flammable liquids are categorized based on their flash points and vapor pressures as defined by NFPA 30 standards.
Class I Flammable Liquids:
- These liquids have a closed cup flash point below 100°F (37.8°C) and a vapor pressure less than 40 psig (275.8 kPa) at 100°F (37.8°C).
- Subcategories:
- Class IA: Flash Point < 73°F (22.8°C) and Boiling Point (BP) < 100°F (37.8°C)
- Class IB: Flash Point < 73°F (22.8°C) and Boiling Point ≥ 100°F (37.8°C)
- Class IC: Flash Point ≥ 73°F (22.8°C) and < 100°F (37.8°C)
Class II Liquids:
- These liquids have a closed cup flash point of 100°F (37.8°C) or higher, but less than 140°F (60°C).
Class IIIA Liquids:
- These liquids have a closed cup flash point of 140°F (60°C) or higher, but less than 200°F (93.3°C).
Class IIIB Liquids:
- These liquids have a closed cup flash point of 200°F (93.3°C) or higher.
Classification of Hazardous Locations - Class I
Class I, Division 1 Areas:
- A location in which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors can exist under normal operating conditions, or
- Ignitable concentrations of such flammable gases, flammable liquid-produced vapors, or combustible liquids above their flash points may exist frequently because of repair or maintenance operations or because of leakage, or
- Breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors and might also cause simultaneous failure of electrical equipment in such a way as to directly cause the electrical equipment to become a source of ignition.
Class I, Division 2 Areas:
- A location in which volatile flammable gases, flammable liquid-producing vapors, or combustible liquid-producing vapors are handled, processed, or used, but in which the liquids, vapors or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems or in case of abnormal operations of equipment, or
- In which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are normally prevented by positive mechanical ventilation and which might become hazardous through failure or abnormal operation of the ventilating equipment or
- That is adjacent to a Class I Division 1 location, and to which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors above their flashpoints might occasionally be communicated unless such communication is prevented by adequate positive pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.
Unclassified Areas:
- Areas where materials are stored in sealed containers (bags, drums, fiber packs on pallets or racks).
- Areas where materials are transported in well-maintained closed piping system.
- Areas where palletized materials with minimal dust are handled or used.
- Areas where closed tanks are used for storage and handling.
- Where dust removal systems prevent the following:
(a) Visual dust clouds
(b) Layer accumulations that make surface colours indiscernible and
- Where excellent housekeeping prevents the following:
- Visual dust clouds
Layer accumulations that make surface colours indiscernible
- Visual dust clouds
Using Ventilation as a Mitigation:
- Inadequate ventilation can lead to larger or stricter area designations for hazardous locations.
- High ventilation rates can sometimes downgrade the classification of an area to “unclassified” when the area is of negligible extent.
- Such high ventilation rates are typically achieved through local mechanical ventilation systems.
- Availability of ventilation is crucial for maintaining safe conditions in hazardous areas.
- According to NFPA 497 standards, adequate ventilation equates to:
- 6 air exchanges per hour,
- 1 cubic foot per minute (cfm) per square foot of floor area,
- Keeping gas/vapor concentrations below 25% of the Lower Explosive Limit (LEL).
Types of Protection: Intrinsically Safe
Equipment designed for hazardous areas with intrinsically safe barriers includes:
- 4 to 20 mA DC Instruments
- Two Wire Transmitters
- Thermocouples
- Resistance Thermometer Detector (RTD)
- Strain Gauges
- Pressure, Flow, & Level Switches
- I/P Converters
- Proximity Switches
- Infrared Temperature Sensors
- Potentiometers
- LED Indicating Lights
- Magnetic Pickup
- Flowmeters
Selection of Electrical Equipment – Class I Areas
Division 1:
- Explosion-proof
- Intrinsically safe
- Purged or pressurized (Type X or Y)
- NEMA 7: Explosion-proof
Division 2:
- Any suitable for Division 1
- Hermetically sealed
- Non-incendive
- Non-sparking
- Purged or pressurized (type Z)
- Sealed device
- NEMA 7
- NEMA 6 and 6P, Liquid-Tight; Vapor-Tight
- Maximum surface temperature must be less than the Auto-Ignition Temperature (AIT) of the gas or vapor as determined by testing
- Appropriate equipment is determined by its T-Code
Temperature Class (“T” code) T-Codes are determined by the maximum surface temperature of the mechanical equipment. Equipment should be selected based on the Auto Ignition Temperature (AIT) of gases and vapors, or the Layer Ignition Temperature (LIT) of dusts. The tables below show this:
Effectively managing hazardous electrical areas is crucial for ensuring safety and preventing accidents in environments where flammable gases, vapors, or dust are present. Understanding the unique risks associated with these areas and implementing appropriate safety measures can significantly mitigate potential dangers. Key considerations include recognizing the hazards posed by electrical equipment, adhering to legal requirements, and following proper classification systems for hazardous locations. By equipping themselves with this knowledge, organizations can enhance operational safety and compliance, fostering a secure working environment.
