What is an SCBA Cascade System?
An SCBA Cascade System is a specialized air delivery system that is designed to provide a constant supply of breathable air in an atmosphere that is immediately dangerous to life or health (IDLH). The system is frequently used in the oil and gas industry to allow workers to perform tasks for extended periods of time in high H2S environments where normal SCBAs can't protect them for the required amount of time.
When installed and used correctly, an SCBA Cascade System offers a high level of protection against respiratory hazards. Also known as a Breathing Air Cascade System or simply Cascade Air System, it is also used by firefighters, SCUBA divers, and HAZMAT teams to get their jobs done safely.
Self-Contained Breathing Apparatuses (SCBAs) offer the advantage of unrestricted movement because they have their own portable air cylinder. However, these units are not suitable for continuous, long-term use in hazardous environments because of their short service life.
If a job requires continuous respiratory protection for an extended period, it is necessary to connect the SCBA's facemask to an external source of breathable air via an airline hose. This can be accomplished using larger capacity breathing air cylinders that are placed outside the danger zone and refilled with a specialized breathing air compressor. The whole system is referred to as SCBA Cascade System.
SCBA Cascade System Components
An SCBA cascade system has the following components:
1. SCBA or SABA
A self-contained breathing apparatus (SCBA) is a type of respirator and is a crucial component of any breathing air system. It consists of three main parts: a face mask, a cylinder of compressed breathable air that is worn on the back, and a regulator to control the flow of air into the mask. Together, these parts work to provide a reliable supply of breathable air for a limited time in potentially hazardous environments.
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| An oil & gas worker wearing Self Contained Breathing Apparatus (SCBA) |
2. Automatic Switch Valve (ASV)
To connect the self-contained breathing apparatus (SCBA) to a cascade air system, a device called an automatic switch valve (ASV) is used. The ASV is installed between the face mask and the SCBA cylinder and serves to connect the facemask to the external air source or, in an emergency, to the SCBA's own air cylinder. By facilitating this connection, the ASV ensures that the user has a constant supply of breathable air.
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| Automatic Switch Valve (ASV) |
In environments where the work is physically demanding and the risks are high, such as high H2S environments, a supplied air-breathing apparatus (SABA) may be used. This type of SCBA features a smaller, lighter cylinder that is worn on the waist. The cylinder is only intended to provide air in emergency situations or when there are problems with the external air supply.
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| An oil & gas worker wearing Supplied Air Breathing Apparatus (SABA) |
3. Breathing Air Manifold
When working in hazardous environments, it is often necessary for multiple workers to wear respiratory protection. Ensuring that these respirators receive a proper supply of air is crucial for the safety of the workers. This is where the breathing air manifold comes in.
A breathing air manifold is usually installed close to the work area and is equipped with 3, 6, or 12 quick-connect couplings that allow it to easily connect to multiple SCBA or SABA equipment. The types of quick-connect couplings depend on the respirator manufacturer.
However, it is very important that the couplings must be incompatible with the outlets of other gas systems in the area to prevent accidental connection with the respirator. An accidental supply of inert gases like helium, argon, or nitrogen, which are often used in industrial applications, to a respirator can be fatal.
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| Breathing Air Manifold |
4. Breathing Air Hoses
Breathing air hoses are another vital component of the SCBA cascade system, as they connect respirators to air manifolds and air manifolds to external large-capacity cylinders. These hoses are made of specialized materials that are usually antistatic to reduce the risk of fire. Some hoses may also be made of flameproof materials for specialized applications such as firefighting.
These hoses are typically available in lengths of 25, 50, 100, and 150 feet and can be connected to one another as per distance requirement. However, once the worker connects to the cascade air system, the maximum hose length should not exceed 300 feet. Table 8 of 42 CFR part 84 Subpart J is an important reference to understand the breathing air hose length requirements.
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| Connecting breathing air hose with SABA |
5. Air Pressure Regulators
Air pressure is an important factor to consider when using SCBA cascade systems. Breathing air cylinders can reach pressures up to 6000 psi. While the lung demand valve (LDV) of the facepiece of SCBA or SABA operates at a pressure between 80 and 125 psi. Also, the air line pressure should never exceed 125 psi due to safety requirements.
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| Lung Demand Valve (LDV) of a SABA |
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| Breathing air regulator |
6. High-capacity BA Cylinders
These compressed air cylinders, which can hold up to 500 cubic ft of air at a pressure of 6000 psi, are connected in a series, and the air is drawn through a pressure regulator before being supplied to the user. When the air in one cylinder is depleted, the operator can switch to the next cylinder to maintain a constant supply of air.
Cascade systems typically include one or more racks of cylinders, called "batteries," which can hold 4, 6, or 8 cylinders each. Multiple batteries can be used to ensure an uninterrupted supply of air, with one battery supplying air while the other is refilled. The number of batteries needed depends on the number of users, the required duration of the air supply, and the BA compressor flow rate.
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| Large Capacity Breathing Air Cylinders |
7. Breathing Air Compressor
The Breathing Air Compressor is the last but most essential component of the SCBA cascade system, responsible for filling the BA cylinder batteries. It is usually electricity or engine driven and installed at a safe distance away from the danger zone in a clean environment.
You must be aware that standard compressed air is not necessarily clean. The compression process can actually increase the concentration of contaminants present in the air and introduce new elements such as oil vapor, condensed water, toxic gases, and bacteria. These contaminants can have both short-term and long-term adverse effects on the health of the users.
To address this, Breathing Air Compressors are equipped with specialized filters and absorbents to ensure that the air they provide is safe to breathe.
It is important to note that the air that is used for breathing and is compressed must meet the standards for Grade D breathing air, which are outlined in the ANSI/Compressed Gas Association's Commodity Specification for Air (G-7.1-1989).
The oxygen concentration in the air must be between 19.5% and 23.5%. The air must also contain no more than 5 milligrams of hydrocarbons per cubic meter, 10 ppm of carbon monoxide, 1,000 ppm of carbon dioxide, and must not have any noticeable odors.
SCBA cascade systems are essential for protecting workers in environments where hydrogen sulfide (H2S) gas may be present. H2S is a highly toxic gas that can pose a significant risk to workers. It is crucial that all workers who may need to use an SCBA cascade system in H2S environments receive training on H2S awareness.
If you are interested, you can get yourself trained in this free online Hydrogen Sulfide (H2S) awareness course.
