What Does SCBA stand for?

SCBA stands for Self-Contained Breathing Apparatus.

If the acronym sounds familiar, it's probably because you're familiar with SCUBA, a specialized type of self-contained breathing apparatus that is designed for underwater use.

While the underwater variety is often used for recreation most SCBA devices are used in workplace safety contexts. That's why they're sometimes called "industrial breathing sets."

What is an SCBA and How Do SCBAs Work?

Although the acronym probably clues you in, SCBA's definition is a type of respirator worn to provide breathable air in environments that might otherwise be dangerous to life or health.

That includes environments that are oxygen-deficient or where the air contains smoke, dust, dangerous gases and vapors, or other airborne contaminants.

SCBA Components

A self-contained breathing apparatus has four main components:

• A face mask or mouthpiece with connected air supply pipes,
• A pressure regulator,
• A carrying frame or pack, and
• One or two high-pressure tanks with compressed air or oxygen

SCBAs and supplied air respirators both supply an outside source of breathable air, which is perfect for situations where the worksite's air can't be made safe through filters or purification systems.

Supplied-air respirators tether the user to a remote air source. Since they don't have to carry their air, they retain greater mobility within the supply hose's range, and it's possible for them to use a larger air supply. The downside is that the air-supply lines can get tangled or caught on objects. The tether also dictates how far users can go from the remote supply.

Since an SCBA relies on tank storage, users are limited to what the amount of air they can carry. There's less chance of entanglement, and there's no distance restriction (except what's imposed by how much air you have left). On the other hand, SCBAs can limit workers' mobility because the tanks are bulky and heavy.

To maximize the available air supply in a tank, gases are compressed to a greater pressure than the human body can safely use. The regulator's job is to elevate the air pressure to a breathable level.

Types of Breathing Apparatus

There are a few different ways to divide up the types of SCBA devices: system pressure, closed- or open-circuit, and escape vs entry-and-escape.

Positive Pressure vs Negative Pressure

Respirators in general can be "positive-pressure" or "negative-pressure." Most air-purifying respirators are negative pressure, while supplied-air respirators and SCBAs can be either positive or negative.

In a positive-pressure respirator, the air pressure inside the facepiece is consistently higher than the outside air pressure. In a negative-pressure respirator, a user's inhalations reduce the air pressure inside the facepiece to dip below the atmospheric pressure.

Here's why it matters. In a negative-pressure system, any cracks in the hose lines or leaks around the facemask seal will allow contaminated air to be drawn into the system each time the user inhales. A negative-pressure respirator can endanger the wearer if the environment is immediately dangerous to life or health (IDLH).

High internal air pressure keeps contaminated air out in a properly functioning positive pressure system. That's why positive-pressure systems are required for IDLH environments.

Open-Circuit vs Closed-Circuit Breathing Apparatus

Open-circuit and closed-circuit breathing apparatuses differ in how they deal with the user's exhalations.

In an open-circuit SCBA, exhaled air is vented directly into the ambient atmosphere. Since the volume of supplied air is "single use," tanks go empty faster in an open-circuit system. They're better for shorter-use situations.

In a closed-circuit SCBA, exhaled air is retained, filtered, supplemented, and recirculated, which is why they're also called "rebreathers." Closed-circuit SCBAs are more complicated because they need a scrubber to remove carbon dioxide and a way to add oxygen back into the recycled air. On the upside, they can be used for a much longer duration.

Escape-Only vs Entry-and-Escape SCBA Devices

Escape-only SCBAs are intended as a backup for situations where a worksite's entry conditions don't call for SCBA protection but where it may become necessary in an emergency.

Escape-only SCBAs are often continuous-flow devices with a hood (rather than a facemask) that can be put on quickly and easily. However, they may also be attached to other types of respirator systems as an emergency backup. Level A or Level B HazMat suits must have an escape SCBA if they rely on a positive-pressure supplied-air respirator.

Since they're intended for shorter durations, escape-only SCBAs may be open-circuit or have a smaller air supply.

Other SCBA systems are sometimes called entry-and-escape SCBAs to distinguish them from the escape-only type. Entry-and-escape SCBAs should be used when you know a worker will need SCBA protection for the duration of their work. They may be open-circuit or closed-circuit and probably have a larger air supply.

Where Are SCBAs Used, and By Whom?

Firefighter SCBAs are the most common example to which most people can connect – everyone can picture a firefighter's oxygen mask and tank.

A firefighter SCBA is typically a positive-pressure open-circuit breathing apparatus with a full facepiece. But SCBAs for firefighting have to meet requirements that industrial SCBAs don't.