Understanding the Storage and Discharge of Liquid Carbon Dioxide

Properties of Carbon Dioxide: Storage and Discharge

Carbon dioxide (CO₂) is stored and discharged under specific conditions to ensure safety and effectiveness in fire suppression. Its storage methods and discharge properties are critical in maintaining its effectiveness as a fire-extinguishing agent.

Storage of Liquid Carbon Dioxide

Liquid carbon dioxide can be stored in high-pressure cylinders or low-pressure refrigerated containers. High-pressure cylinders have a storage temperature that varies with the surrounding environment, while low-pressure systems are designed to maintain a storage temperature of approximately 0°F (-18°C).

High-pressure cylinders typically range from 5 lb (2.27 kg) to 120 lb (54.4 kg) in capacity, whereas low-pressure storage units have capacities ranging from 750 lb (340 kg) to a massive 60 tons (54,431 kg) per unit.

High-pressure cylinders are equipped with siphon tubes that draw liquid CO₂ from the bottom of the cylinder. The contents are then discharged through a control valve to the fire zone. When the discharge valve opens, the entire content is typically released.

Discharge Properties

The discharge of liquid carbon dioxide has a white, cloudy appearance due to the formation of a water fog as the air is cooled below its dew point. This fog results from both the cooling of the air and the fine dry ice particles produced. The water fog can persist for a time after the dry ice particles have sublimed.

Even after the fog dissipates, dangerous concentrations of CO₂ may remain in the area, making proper ventilation crucial during and after discharge.

Static Electricity Concerns

During the discharge process, dry ice particles can accumulate static electricity. Additionally, static charge can build up on ungrounded discharge nozzles. To avoid the risk of electric shocks or unwanted static discharges—especially in explosive environments—all discharge nozzles must be grounded.

Vapor Density of CO₂

Carbon dioxide vapor is much denser than air. Its density is one and a half times greater than air at the same temperature. As CO₂ vapor discharges to the atmosphere, it can approach temperatures as low as -110°F (-79°C), making it denser than the surrounding air. This greater density allows CO₂ to replace the oxygen above burning surfaces, maintaining a smothering atmosphere and effectively suppressing the fire.

Physiological Effects of Carbon Dioxide

Carbon dioxide is a natural component of Earth's atmosphere, typically present at 0.04%. It is also a normal by-product of cellular respiration in both humans and animals. In the human body, CO₂ plays a crucial role in regulating breathing, ensuring a sufficient supply of oxygen to the system.

© 2024 Knowledge on Carbon Dioxide Properties. All rights reserved.

Storage of Liquid Carbon Dioxide

Which of the following statements about the storage of liquid carbon dioxide is correct?

High-pressure cylinders typically have a capacity ranging from 750 lb (340 kg) to 60 tons (54,431 kg).
Low-pressure storage units are designed to maintain a storage temperature near 0°F (-18°C).
High-pressure cylinders do not require siphon tubes for discharge.
The discharge of carbon dioxide from storage cylinders has a white, cloudy appearance due to water fog.

CFPS QUIZ "Comprehensive Quiz on the Properties and Safety of Carbon Dioxide as a Fire-Extinguishing Agent

Quiz on Carbon Dioxide Properties as a Fire-Extinguishing Agent

Carbon dioxide (CO₂) is an effective fire-extinguishing agent due to its various properties. It is non-combustible, does not react with most substances, and provides its own pressure for discharge. As a gas, CO₂ can easily penetrate fire areas and is capable of suppressing flames by displacing oxygen. It is safe to use on energized electrical equipment as it does not conduct electricity. Additionally, it leaves no residue, eliminating the need for cleanup. CO₂ has unique thermodynamic properties. At room temperature and pressure, it is a colorless and odorless gas. It can be easily liquefied by compressing and cooling, and further compression and cooling can turn it into a solid. Its pressure and temperature influence its state (gas, liquid, or solid), with transitions occurring at critical points, including the triple point.

Multiple-Choice Questions

1. Which of the following properties makes carbon dioxide an effective fire-extinguishing agent?

• a) It reacts with most substances.
• b) It can conduct electricity and is safe for electrical equipment.
• c) It leaves no residue after use.
• d) It requires an external source of pressure for discharge.

Answer: c) It leaves no residue after use.

2. What state does carbon dioxide exist in above the critical temperature of 87.8°F (31°C)?

• a) Solid
• b) Liquid
• c) Gas
• d) Gas and liquid

Answer: c) Gas

3. At what temperature does carbon dioxide exist in all three phases (gas, liquid, and solid) simultaneously?

• a) -69.9°F (-57°C)
• b) 0°F (-18°C)
• c) 87.8°F (31°C)
• d) 75 psia (517 kPa)

Answer: a) -69.9°F (-57°C)

4. What happens to liquid carbon dioxide when it is discharged into the atmosphere?

• a) It remains as a liquid and evaporates slowly.
• b) It instantly flashes to vapor and a portion becomes dry ice (snow).
• c) It freezes into solid dry ice immediately.
• d) It solidifies into a compact block.

Answer: b) It instantly flashes to vapor and a portion becomes dry ice (snow).

5. What is a critical safety measure when discharging carbon dioxide?

• a) The discharge nozzles should be insulated.
• b) The nozzles must be grounded to prevent static electricity buildup.
• c) The system should be pressurized with air.
• d) Discharge should be performed in an open area to avoid contamination.

Answer: b) The nozzles must be grounded to prevent static electricity buildup.

6. What happens to the density of carbon dioxide vapor when it is discharged at very low temperatures?

• a) It becomes lighter than air and rises.
• b) It maintains the same density as the surrounding air.
• c) It becomes much denser than air and sinks.
• d) It disperses evenly in the atmosphere.

Answer: c) It becomes much denser than air and sinks.

7. What is the standard storage temperature for low-pressure carbon dioxide containers?

• a) 87.8°F (31°C)
• b) 0°F (-18°C)
• c) -69.9°F (-57°C)
• d) 70°F (21°C)

Answer: b) 0°F (-18°C)

© 2024 Fire Safety Knowledge Quiz. All rights reserved.

CFPA EXAM :Fire Pump Installation Quiz: Test Your Knowledge on Power Supplies and Standards

Fire Pump Installation Quiz

1. Among acceptable power supplies for fire pumps, which can be used as a stand-alone power source without a backup?

• a) Battery backup system
• b) Solar panels
• c) Reliable utility service
• d) Hybrid power system

Answer: c) Reliable utility service

2. According to NFPA 70, Article 100, a service begins where the utility wiring stops. This point is referred to as the:

• a) Service disconnect
• b) Service point
• c) Load center
• d) Circuit breaker

Answer: b) Service point

3. For fire pump installations, electrical power should ideally be provided through:

• a) A shared circuit with other equipment
• b) A battery backup system
• c) A dedicated circuit to the fire pump controller
• d) A general-purpose extension cord

Answer: c) A dedicated circuit to the fire pump controller

4. The service equipment for fire pump installations should be located to:

• a) Increase power efficiency
• b) Minimize the possibility of damage by fire
• c) Allow easy access for maintenance
• d) Support multiple electrical loads

Answer: b) Minimize the possibility of damage by fire

5. On-site electrical power production includes:

• a) Utility-provided power
• b) Renewable energy from off-site sources
• c) Prime movers and generators located on the premises
• d) Electrical power purchased from third-party vendors

Answer: c) Prime movers and generators located on the premises

6. What is the primary role of on-site generation in fire pump installations?

• a) To supplement utility power during peak hours
• b) To supply all electrical loads in the facility
• c) To reduce energy costs
• d) To ensure compliance with NFPA 70

Answer: b) To supply all electrical loads in the facility

7. What is the connection method for electrical power when a dedicated service is not possible for fire pump installations?

• a) Tap ahead of the service disconnect
• b) Shared connection with general building circuits
• c) Connection via an extension cord
• d) Integration with solar inverters

Answer: a) Tap ahead of the service disconnect

NEC 314.27 Outlet Box Requirements for Luminaires and Ceiling Fans

Understanding NEC 314.27: Requirements for Outlet Boxes

The NEC 314.27 outlines the standards and requirements for outlet boxes used to support electrical fixtures like luminaires, ceiling fans, and other utilization equipment. These regulations ensure that the outlet boxes are adequately rated for the weight and installation of electrical equipment, preventing potential hazards such as equipment failure or electrical fires.

A) Boxes at Luminaire or Lampholder Outlets

• Vertical Surface Outlets: Outlet boxes must be marked with the maximum weight they can support if different from 23 kg (50 lb).
• Exception: Luminaires or lampholders that weigh no more than 3 kg (6 lb) can be mounted on other boxes, provided they are securely fastened with at least two screws.
• Ceiling Outlets: The box must support a luminaire weighing a minimum of 23 kg (50 lb). If the luminaire weighs more, it must be independently supported unless the outlet box is rated for the additional weight.

B) Floor Boxes

Floor boxes used for receptacles must be specifically listed for this application. If located in elevated floors of show windows or similar locations, the authority having jurisdiction may permit other boxes as long as they are not exposed to physical damage, moisture, or dirt.

Exception: In some cases, receptacles and covers in elevated floors may use boxes that are not listed for floor applications, provided they are not exposed to damage.

C) Boxes at Ceiling-Suspended (Paddle) Fan Outlets

• Ceiling-Fan Boxes: The outlet boxes must be listed for ceiling fans and marked by the manufacturer to indicate their suitability for this purpose. The maximum weight supported is 32 kg (70 lb).
• For heavier fans: If the ceiling fan weighs more than 16 kg (35 lb), the box must include a weight limit marking.

D) Utilization Equipment

Boxes supporting other equipment must meet the same weight requirements as those supporting luminaires of similar size and weight.

Exception: Equipment weighing no more than 3 kg (6 lb) can be mounted on other boxes or plaster rings, as long as they are secured with at least two screws.

E) Separable Attachment Fittings

Outlet boxes may also support listed locking support and mounting receptacles used with compatible attachment fittings. These must be identified for use within specific weight and mounting orientation limits. When a supporting receptacle is installed within a box, it must be included in the fill calculation for box size.

Key Takeaways

The guidelines in NEC 314.27 are essential for maintaining safe electrical installations. Ensuring that outlet boxes are correctly rated and marked according to the weight and type of equipment they will support can help avoid electrical failures, fires, and other hazards. Always ensure you choose the correct outlet box based on the manufacturer’s specifications to ensure safety and compliance with NEC regulations.

These requirements help ensure long-term safety and performance in residential, commercial, and industrial electrical systems.

© 2024 NEC Electrical Installations. All Rights Reserved.

Understanding NEC 408.4: Proper Circuit Identification for Electrical Safety and Compliance"

Understanding NEC 408.4: Importance of Proper Circuit Identification for Electrical Safety

Proper circuit identification is essential for ensuring safety, efficiency, and compliance in electrical installations. In this article, we will explore NEC 408.4, which outlines the importance of clear circuit identification in electrical systems. Whether you're an electrician, contractor, or homeowner, understanding these requirements can help avoid costly mistakes and improve the safety of your electrical system.

A) Circuit Directory or Circuit Identification

According to NEC 408.4, proper circuit identification is a critical aspect of electrical systems. Here’s why:

• Clear and Specific Identification: Every circuit, including modifications, must have a clear label indicating its purpose. This helps prevent confusion during installation, maintenance, or troubleshooting.
• Unused Circuits: Spare positions with unused overcurrent devices or switches must be labeled accordingly, ensuring clarity even for future use.
• Panel Directory: A circuit directory must be placed visibly inside the panelboard or near each switch or circuit breaker. This ensures electricians and technicians can quickly identify circuits without wasting time.
• Avoiding Temporary Descriptions: It’s important that circuit descriptions are permanent and do not rely on transient or temporary conditions, such as occupancy.

B) Source of Supply

NEC 408.4 also requires that the power source for electrical devices and equipment be clearly marked:

• Permanent Marking: For switchboards, panelboards, and switchgear, the power source must be permanently marked, especially if supplied by feeders in non-residential settings. This labeling helps ensure proper maintenance and troubleshooting.
• Durability of Labels: Labels must be durable enough to withstand the environment. Avoid handwritten labels, as they can fade or become illegible over time.

Why Proper Circuit Identification Matters

Proper identification of circuits plays a vital role in electrical safety. It allows electricians, maintenance teams, and emergency responders to work efficiently and safely. It’s also essential for preventing errors during repairs, upgrades, or emergency interventions.

By adhering to NEC 408.4 guidelines, you create a more organized and secure electrical system, making it easier to troubleshoot, maintain, and enhance the system in the future.

Spaces About Electrical Equipment.

Requirements for Working Spaces Around Electrical Equipment (NEC 110.26)

This section specifies the requirements for working spaces around electrical equipment operating at 1000 volts or less, ensuring safe operation and maintenance.

General Requirements

• Working spaces must always be maintained around electrical equipment for safe operation and maintenance.
• These requirements apply to equipment likely to require examination, adjustment, or servicing while energized.

(A) Working Space

This subsection defines the dimensions of working spaces required around electrical equipment. Details are as follows:

(1) Depth of Working Space

The depth required depends on the voltage and conditions around the equipment, as outlined in the table below:

Nominal Voltage to Ground	Condition 1	Condition 2	Condition 3
0-150	900 mm (3 ft)	900 mm (3 ft)	900 mm (3 ft)
151-600	900 mm (3 ft)	1.0 m (3 ft 6 in)	1.2 m (4 ft)
601-1000	900 mm (3 ft)	1.2 m (4 ft)	1.5 m (5 ft)

Notes on Depth:

• Dead-Front Assemblies: No rear/side working space is required if all maintenance is done from the front.
• Low Voltage: Smaller working spaces are allowed for live parts ≤30V RMS, ≤42V peak, or ≤60V DC.
• Existing Buildings: Reduced clearance is permitted with written maintenance procedures.

(2) Width of Working Space

The width must be at least 762 mm (30 in.) or the width of the equipment, whichever is greater, and must allow doors/panels to open at least 90 degrees.

(3) Height of Working Space

• Working space must extend from the floor to 2.0 m (6.5 ft) or the height of the equipment, whichever is greater.
• Equipment associated with the installation may protrude up to 150 mm (6 in.) beyond the front.
• Exceptions:
  • Panels ≤200A in existing dwellings.
  • Meters installed in meter sockets.
  • Open battery racks follow 480.10(D) clearance requirements.

(4) Limited Access

When equipment is installed in spaces with limited access:

• Ceiling openings must be at least 559 mm × 559 mm (22 in. × 22 in.), or crawl space openings must be 559 mm × 762 mm (22 in. × 30 in.).
• Working space width must be at least 762 mm (30 in.) or the width of the equipment, whichever is greater.
• Doors/panels must open at least 90 degrees.
• Depth must follow the requirements in the table above.