How Non-Rebreather Masks Work

Non-Rebreather Mask:

The Non-re Breather (NRR) or “No Re” means that it does not contain any kind of air filter, which helps prevent inhaling harmful particles from the outside world. These are usually found in dust, smoke, pollution and other airborne pollutants. Some NRR masks have a small opening on top where you can breathe through. Others do not allow you to breath at all.

They are commonly used in areas with high levels of pollution such as factories, power plants, smoggy cities and even some military bases.

A non-rebreather mask is one that does not contain any kind of filters or devices that remove particulate matter from the air. Instead they rely on the natural ability of your lungs to expel these particles out. The most common type of NRR mask is called a partial rebreather. A partial rebreather uses a fan to force fresh air into the mask while filtering out the harmful particles that may still remain inside.

In order for a person wearing a NRR mask to breathe normally, they must first open up their mouth so that you can blow into it. The term used to describe the process of removing contaminated air from the inside of a non-rebreather mask is called bypassing. This occurs when the clean breathing air mixes with or displaces the contaminated air from your lungs. The longer you wear a NRR mask, the more contaminated air you will eventually inhale.

This is why it is important to check and see if there are any areas where clean air exists, and move towards them as needed. If there are no clean air zones found, then you can still survive for at least 48 hours without suffering any ill effects. After this time period, it is suggested that you find a better respirator or move to a better environment. Otherwise your lungs will be severely damaged.

A person that uses this type of mask should avoid staying in an environment with heavy smoke or other airborne hazards for long periods of time.


A rebreather is a device that is used to recycle exhaled carbon dioxide, cleaning out the waste products of breathing before allowing it to be breathed in again. A gas mixture containing oxygen and some other breathable gas is kept at a higher pressure than the surroundings and this difference is what drives the process. This type of device is most commonly used by scuba divers that are submerged at depth below about 20 feet (6 meters).

The word rebreather is often used to describe two different types of devices: open-circuit and closed-circuit. With an open-circuit device, the diver manually breathes in and out of the device like a standard set of scuba regulators. With a closed-circuit device, the diver wears a full face mask or helmet with a breathing apparatus that has a supply of gas available to it at all times. These types of respirators are not typically used on the land although there are some exceptions such as in a mine or during a fire.

Rebreathers are a diverse group of devices with many variations available. Some can run off of canned air, allowing a diver to maintain a supply of oxygen in tanks on their back. Others can be as small as a pack of cigarettes, allowing divers to maintain breathing while doing very demanding work underwater. The specific type of rebreather that is discussed in detail here is the open-circuit, semi-closed circuit type.

These types of devices allow the diver to take in a mixture of oxygen and another gas such as Nitrox for long periods of time. The gas cylinders attached to these devices are often used up quite quickly though, so a diver needs to frequently be connected to an external supply of breathing gas.

Rebreathers have a very important advantage over normal scuba equipment in that they are much lower in profile and produce very little noise. Nothing attracts the attention of an infected person like the sound of a diver with heavy equipment clunking around. Using a rebreather can allow a person to remain undetected from hundreds of feet away. Most rebreathers are also fully self-contained, allowing them to be run without anyone else’s help.

When selecting a rebreather, the important thing to look for is the amount of time that it can be used without any additional gas. This number is given in minimum times for which the unit can be used based on the capacity of the cylinder that is connected to it. A small unit might be able to run for 40 minutes while a large one might be able to run for over 4 hours. Another number that is also important is the amount of gas that is added with each breath.

If the unit is constantly being used, it will eventually run out of gas, so the capacity of the unit needs to be known before you can make an accurate guess at how long it will last.

Rebreathers also require a thorough cleaning and maintenance from time to time. This process can take some time and needs to be done carefully to ensure proper function. Without this care, the device might not work when needed which would be a fatal mistake.

A rebreather is a very useful tool to have in the right situation. They can allow you to explore underwater locations that would otherwise be completely inaccessible. They are also great for anyone trying to avoid large numbers of infected where noise would give away your position. A word of caution, however; when times are tough and food is running low, a full face mask can make grabbing the supplies off of a dead body much harder than with an open face diving helmet.

Be sure to keep this in mind when the time comes.

You have a limited number of diving suits and rebreathers due to their specialized nature, so you will need to make the most of them. Divers are often given more rations and time to rest when there is an ample supply of gas for rebreathers.

Also keep in mind that although these devices allow you to stay under water for extended periods of time without any ill effects, they do not protect you from the other dangers of an underwater environment. There are still sea creatures, low visibility, strong currents, and other hazards that can kill a person in the same way as they would on land. Always watch your step!

Good luck, dive safe, and have fun!

Table of Contents

1. Introduction

2. How To Use This Document

3. Types Of Diving

3a. Scuba (Self Contained Underwater Breathing Apparatus)

3b. Snorkeling (Using A Snorkel Rather Than A Full Face Mask)

4. Equipment

4a. Equipment Descriptions

4b. Scuba and Snorkeling Gear

4c. Rebreathers

4d. Scuba Tabs

5. Dangers And Precautions

5a. Hazards and Killers

6. Diving Tips and Techniques

7. Infected Water Creatures

7a. Fish

7b. Cnidarians (Jellyfish, corals, anemones)

7c. Annelids (Lobster, squid, etc)

7d. Mollusks (Bivalves and other single shell creatures)

8. Exotic Water Creatures

9. Strange Creatures

10. Unique or Unusual Situations

11. Acknowledgements

1. Introduction

Diving has been a part of human culture as long as there have been humans. Our history is riddled with accounts of people drowning and even thriving underwater. Whether by necessity or curiosity, people have always wanted to explore what lies beneath the surface of the water.

With the discovery of the so called “Floating Mist” islands and the revelation that an entire unexplored world exists at the bottom of our oceans, diving has taken on a new role in human culture. Whether for exploration, salvage, tourism, or even just for fun, humans have taken to diving as a past time like none other.

This guide will teach you everything you need to know about the equipment used for diving and how to stay alive while doing it. Remember, diving can be extremely fun but also very dangerous if certain precautions are not taken.

2. How To Use This Document

This guide follows a general rule of using real world terminology wherever possible.

Sources & references used in this article:

Evaluation of the self-inflating bag-valve-mask and non-rebreather mask as preoxygenation devices in volunteers by A Robinson, A Ercole – BMJ open, 2012 –

Reliability of methods to estimate the fraction of inspired oxygen in patients with acute respiratory failure breathing through non-rebreather reservoir bag oxygen mask by R Coudroy, JP Frat, C Girault, AW Thille – Thorax, 2020 –

Methods for evaluation of helium/oxygen delivery through non-rebreather facemasks by AR Martin, IM Katz, Y Lipsitz… – Medical gas …, 2012 – medicalgasresearch.biomedcentral …

Effect of preoxygenation using non-invasive ventilation before intubation on subsequent organ failures in hypoxaemic patients: a randomised clinical trial by C Baillard, G Prat, B Jung, E Futier, JY Lefrant… – British journal of …, 2018 – Elsevier

Respiratory support for adult patients with COVID‐19 by JS Whittle, I Pavlov, AD Sacchetti… – Journal of the …, 2020 – Wiley Online Library