Choosing Escape Breathing Apparatus
This starts, as with all PPE, with a specific risk assessment. I know I always state this, but if this is done correctly it will lead you to make the correct selection. There are really 3 types of escape set, also known as ELSA (Emergency Life Saving Apparatus) on the market produced in slightly different looks by all of the major players. These are the constant flow hood type, positive pressure full face mask and chemical re-breathers. Each has good and bad points and so long as these are understood then ensuring wearer safety should not be difficult. So I will break them down and deal with them by group and start with re-breathers.
Chemical re-breathers are usually fairly small and easy to wear providing various duration's but usually from 20 to 100 minutes. This is achieved by breathing into a tube which then fills a bag which contains KO2. There is then a chemical reaction which converts your expelled carbon dioxide into oxygen and this is drawn back through the same tube.
These units can be very basic and just have a nose clip, some also have goggles or even a hood. Some units that have a cartridge that inflates the bag, though this really is to counteract the feeling to the untrained that the unit is not working. This is because at start up the non cartridge type bag will remain fairly flat against the chest for a while and this can panic the user. But if training is done correctly they should understand this.
The advantages of these sets are the duration times that they offer and the fact that they are categorized as a working set as well, so you could ask the wearer to perform a task unlike normal escape sets which are strictly for escape only. They also have fairly simple checks to ensure they are safe to use which is usually a form of tag or seal which must not be broken, some also have colour change indicators built in as leaking seals would render the set useless.
The problems associated with these sets are duration times are based on levels of distress, so whilst you may achieve the longest time your risk assessment should really be based on the shortest. The air delivered is fairly hot and can be uncomfortable to breathe. The sets are usually a one use only so false alarms or mistreatment can result in a large cost. The sets usually suit tunnelers or miners due to the small size they do not hamper the worker and offer a duration that should make the escape time sufficient to reach safety. Things to be aware of, is eye protection required and some wearers may feel sick with the tube in their mouth.
Positive Pressure Full Face Mask Sets
Positive pressure full face mask type escape sets offer the same protection as a full breathing apparatus set. They are provided with compressed breathable air from a cylinder through a reducer to a demand valve that allows the volume of air that you require to be delivered to you. There is a positive pressure supplied to the face mask which ensures that should the mask fail or not be fitted correctly that the debris or toxins are blown away from the wearers inhalation. The cylinder has a pressure gauge fitted as for all compressed air escape sets, this will be a simple use or do not, usually with a green area showing that it is full and safe for use.
These sets can only be used for escape and if any task is required to be done other than escape you have provided the wrong equipment.
The good points are they provide maximum protection to the wearer and have built in speech diaphragms so you can communicate with other members of the team fairly easily when wearing them. Once used re-charging is simple with little cost. They usually offer good visibility though this can depend on the mask that you choose. Donning or putting the set on is fairly simple and they can come in different types from shoulder bags to jerkins.
They usually offer 10 or 15 minutes although there are some that offer 20 minutes. This is always a trade off as greater duration requires a larger cylinder or the composite option. A very experienced wearer may get longer duration's because they fully understand the physiology of breathing.
Down sides are the wearer must be clean shaven and spectacles are a problem. The demand valve will deliver what the wearers lungs demand but the time duration is based on an average man walking at average speed under average duress. As any one who has done this for some time will know, in a real emergency most wearers will be anything but average. This means that duration time could be as little as half and this will be dependent upon the wearer. Because the set has a positive pressure if the mask is fitted incorrectly then air will flow straight out again reducing wearer time. The last breathe of air consumed on a mask type set will suck the mask onto the wearers face and can deliver nothing else.
I personally feel these units should only be worn be people trained to use full BA as the only difference between the donning checks is there is no whistle on a mask type escape set.
Constant Flow Escape Sets
The constant flow escape set delivers compressed breathable air through a controlled outlet to a hood with a rubber neck seal. This sounds crude, which it is, but it is also very effective. Whilst it does not provide a positive pressure it does guarantee the wearer the time stated, as the time is not based on the individuals consumption as the sets valve provides 40 litres per minute average. So you will get 10 minutes with a 10 minute set and 15 with a 15 regardless of how much you mess up putting it on, time is again dependent on cylinder size.
Unlike the mask type when the air runs out you will still be able to breathe the air contained in the hood. If you leave the hood on, whilst you will pass out, it will give you valuable extra minutes to be rescued and resuscitated with an oxygen therapy unit. This of course should never happen as travel time should be calculated correctly.
These units can be worn by people who wear spectacles and are not clean shaven. Again there are several different wearing styles from shoulder bags to jerkins and selecting the correct option is a must.
The down side to these sets are that the wearer can out breathe the set if panicking causing the hood to contract against the head. This can be easily sorted if good training is delivered as it will highlight this problem. The hood can be large and cumbersome and this will be different with each manufacturer so a good thing to be aware of. Speech being heard is very difficult in the main because the air constantly flows through the hood but there is also no speech diaphragm. Visibility is not as good as with a mask type as the viewing area is usually a clear plastic sheet which can crease causing light marks.
All of these options require good training so that safety is ensured to the wearer. Only when the above concepts are understood can a risk assessment advising the correct emergency escape plan be determined.