Application specific device selection
Breathing Apparatus can be split into varying categories. These include Self Contained Breathing Apparatus (S.C.B.A.), Escape Breathing Apparatus, Filtration Devices, Airline Systems, Fresh Air Devices and Oxygen Rebreathers (K02). We will look at all these devices and go through each apparatus to explain the differences, explain the selection process and, hopefully, ensure that the next time you require any form of Breathing Apparatus (B.A.) you pick the right one for your application.
S.C.B.A. can be divided into two different categories, Fire fighting and Industrial use. In this publication we will try to deal with the Industrial side, however, we will inevitably discuss the fire fighting side as there are many similarities in the equipment and requirements.
Self Contained Breathing Apparatus (S.C.B.A.)
Commonly called S.C.B.A. this is the compressed air fed device that everybody always associates with the Emergency Services and there is a real misnomer that they are complex. The reality is that a full set of S.C.B.A. is user friendly, simple to understand and very comfortable to wear. There are several different types of S.C.B.A, but usually the principles will be the same. Self Contained Breathing Apparatus will always be donned prior to entering an industrial area or an Emergency situation. The mask has a 5-point adjustment to ensure a good fit on the user. Checks to perform prior to entering the area required will involve face fit testing, high pressure leaks, cylinder capacity and pneumatics. Only suitably trained and qualified personnel will be permitted to don S.C.B.A. The Health and Safety Executive (HSE in the UK) deem a competent person to be somebody who is suitably trained or qualified by experience and practical knowledge.
Self Contained Breathing Apparatus (S.C.B.A.) Specific EN137
Starting with the back plate, this is the support for the unit. The back plate carries the cylinder and will also have a harness which attaches to the user. It is imperative that the harness is adjusted to fit the size of the wearer correctly to make the cylinder sit correctly ensuring the weight of the back plate is distributed evenly across the persons’ posture, preventing strains or injury. Some back plates are flexible with internal hinge plates ensuring freedom of movement even in confined spaces. The next thing we need to decide is the duration of air required in the cylinder. This will dictate the size of the cylinder required. Cylinders come in several different sizes, 6 litre, 6.9 litre or 9 litre.
We can also use 2 cylinders on the same back plate if this is a requirement. As we progress in this article we will also look at the use of the 4 hour unit (KO2) which allows the user to have long duration sets if this is required. The Pneumatics, which provides the air to the mask, are already fitted to the back plate and integrated into the pneumatics, is the gauge, which indicates the air pressure and duration of air remaining, until we have to return to our safe area.
Another important part of the set is the face mask. We must consider the type of mask required and this will be dictated by the atmosphere that the user is entering, enabling them to be protected from certain types of toxin, dust vapours, gases etc.
Another option available is the use of Airline Breathing Apparatus. If there is a requirement to enter our work area for a long duration or the area is confined allowing minimal movement that is restricted by wearing a cylinder, we utilise airline systems. This will allow the user to have a large number of options for the use of face masks to ensure that they are safe from the risks related to the task that they are involved in.
For example if they are cutting or welding there are protective hoods that will ensure that ingress of fumes or particulants is prohibited. The airline can be fed by cylinders, a compressor and, in some cases, fresh air with a filter. The cylinders on a “trolley” system will be fitted with an automatic change over valve to ensure continuity of supply. These will require a number of cylinders on site to reach the required level of supply.
The use of a compressor in an airline system is another way of guaranteeing a continuous level of clean air, however mechanical machinery will require monitoring should there be failures or should the fuel supply fail. Fresh air system can either be fed directly or through a unit guaranteeing “forced air” supply.
Compressed Airline Breathing Apparatus EN139
Compressed airline breathing apparatus, according to EN139, function independently of the ambient atmosphere. They can be used in all places where the ambient air is not breathable because of contaminants or oxygen deficiency and where filtering devices do not provide sufficient protection. Compressed air is supplied from an external source (i.e. factory airline), from a compressor or a compressed air cylinder.
Fresh Air Hose Devices EN138
A very simple way of ensuring “clean” breathable air is via hoses. Without any form of blower the user can have anything up to 18m of hose and with a blower it can be up to 54m. The hose is position outside of the hazardous environment, must be fixed to prevent the hose from moving and should be filtered to stop any “foreign bodies” from entering the hose. There is the facility to connect two users to the hose and the mask is usually universal with S.C.B.A.
S.C.B.A. Cylinders EN 144 PED 97/23/EG
Cylinders are available in several sizes and it is imperative to get the right size of cylinder and to make sure that the correct number is on site. Check with the manufacturer that you have your cylinders from and ensure that the duration of the cylinder is acceptable. Also there are steel and composite cylinder options available. Composite cylinders are approximately 50% lighter than the steel versions. This presents rather obvious advantages, however it comes at a cost premium. The cylinders should also clearly have displayed the last date of test. This is a requirement and displays the cylinder life time and next test due date.
Steel cylinders are usually available in 4 litre/200 bar and 6 litre/300 bar sets typically giving anything from 35 to 45 minute durations. The composite cylinders 6, 6.8 and 6.9 litre with 300 bar maximum pressure.
S.C.B.A. Face Masks EN 136, class 3
There is a requirement to carefully choose the type of face mask that is relevant to the task in hand. In some circumstances it may be a requirement to have a “face fit test” to prove the integrity of the fit in relation to the wearer. Guidance is usually given in the Approved Code of Practice (ACOP) in the UK. Sometimes, however it is unclear as to the exact requirements so it is always advisable to seek advice on the site or company policy.
The face mask is generally made of 6 different parts. The Face Blank is made of a special rubber compound which makes it soft and comfortable. It is not affected by creams or lotions. The wide sealing frame and deeper chin stop assure a snug, comfortable fit and, very importantly, a tight seal on the user. The Lens is moulded from impact resistant plastic (polycarbonate) and is securely sandwiched between a groove in the face blank with a 2-part plastic lens ring. The large field of vision provides the wearer with an obvious safety advantage and ensures all round vision to aid them in their task. Some lenses are also available in silicate coated glass or Triplex glass. The Connector is clamped to the face blank. This contains the threaded connection or the plug connection, the inhalation valve and the speech diaphragm. The speech diaphragm permits excellent communication, ensuring that whatever the task the wearer can keep in contact with colleagues, safety personnel, stand by teams etc. The Exhalation Valve is located in the lowest point of the face mask. It is essential that this valve works correctly as this will remove the Carbon Dioxide (CO2) that the wearer breathes out. Although we breathe in around 0.04% CO2, we exhale 4% so it is imperative that the face mask is capable of exhaling this “dirty air”. The Harness enables quick donning and removal (doffing) without prior adjustment. A pressure free fit can also be achieved in combination with a helmet, thus ensuring continuity of protection. Usually the harness has a strap integrated to ensure safe carriage around the chest lowering the risk of damage to the lens. The Inner Mask provides optimal air flow and keeps the lens free from fogging. It reduces the dead space effectively. The rolled edge cares for a soft and comfortable contact with the face.
Chemical Oxygen Breathing Apparatus (KO2) EN401
Self contained chemical Oxygen (K02) breathing apparatus for use in oxygen deficient atmospheres, as well as hazardous atmospheres, containing smoke and toxic gases offer protection for periods of between 15 minutes and 4 hours for a variety of applications ranging from simple assistance and salvage to tough fire fighting and rescue missions. The chemical oxygen apparatus applies the proven principle of regenerating the breathing air with oxygen produced by the chemical Potassium Hyperoxide. Simultaneously retaining the Carbon Dioxide and humidity contained in the exhaled air, these breathing apparatus are very reliable and almost maintenance free for extended storage periods. There are a number of different options available and, as with all Breathing Apparatus, careful selection of the equipment is paramount to ensuring safe “back up” at all times. There is a 4 hour closed circuit breathing apparatus for long duration tasks and rescue. There are units available that will last, from 15 minutes up to approximately 5 hours (at rest) for self rescue. The main advantage to the user with these sets is the service intervals and the cost involved.
Emergency Escape Breathing Apparatus (EEBA) EN1146
Emergency escape breathing devices will enhance the potential for escape from hazardous areas and confined spaces. An integral part of any risk assessment for working in potential hazardous areas must be the consideration of the option for escape (self rescue). The most economical solution is a filtering device. It is perfect as long as you know the type, properties and composition of the hazardous agent in ambient air. If you can’t be sure that it will work in all situations (i.e. low oxygen concentration, <17% Vol 02, high toxic gas concentrations etc.) Therefore a higher level of protection is offered by independent air supply systems (based on compressed air supply or chemical oxygen regeneration).
All these units are designed to be small and neatly packed so that they can be easily placed near or hung up close to the work area. They can then be stored unopened for a long period of time, yet immediately ready for use. There are varying types of unit that offer different time scales of escape. The other large difference is the mask. There are versions with a mouthpiece, nose clip and goggles, half face masks and protective hoods that cover the whole of the breathing zone and face.
We then have Compressed air escape breathing apparatus. Again there are varying types and options available. The most common is the Positive Pressure set. This is commonly fitted with a full face mask and is initiated on the first breath. The main advantage of this set is that air is fed “on demand”. This means that you only use up the air that you require, thus conserving the very commodity that is aiding your escape.
The full face mask must be a good fit and please refer to the previous description regarding face masks. The major difference between S.C.B.A. face masks and E.E.B.A. is that the escape set has only 2 points of adjustment ensuring a quick fit to minimise the risk of ill fitting and ingress of toxic gases. The Provision and Use of Work Equipment Regulations (PUWER) also dictate that the wearer must inspect the equipment prior to use and, as a competent person, must stop any activity if equipment is found to be faulty, damaged or outside of the manufacturers’ recommended service interval.
The other type of compressed air set is a Constant Flow device. This is commonly fitted with a hood instead of a full face mask. Hoods are ideal and fit with the Approved Code of Practice (ACOP) regarding face masks.
This states that anybody with more than 4 days of facial hair, people with glasses or with an “odd shaped face” should not be wearing a face mask. With the constant flow of air the wearer will have a flow of air constantly fed into the hood. The major advantage is that the hood will seal on the neck instead of the face. This ensures the hood will fit everyone regardless of facial hair or feature.
The other advantage is the time it takes to fit the hood. The hood simply fits over the head and can then be adjusted whilst there is air flowing. The full face mask, unfortunately, if fitted incorrectly can result in the compressed air leaking and under pressure, usually 200 bar, will cause the cylinder to empty air very quickly. Less experienced users may panic and this will make the escape process more time consuming and potentially more hazardous. Escape can vary in time scale between 10 minutes and 15 minute sets.
Monitoring systems EN137
The need to monitor and protect wearers is of paramount importance. As part of the rescue team we need to ensure there is no possibility of the rescuers becoming the victim. This means the rescue team have extra pressure placed on them. Using a network system allows the “safety man” or “top man” to monitor the critical information for the operatives. There are a couple of ways of doing this. The old fashioned way is by utilising a board, pen and stopwatch. Write the entrants’ duration of air, time of entry and required time of exit so they do not run out of air. This is crude and sometimes can be either misunderstood or forgotten. The new method is to use a “network” system. This is an electronic device that can be programmed individually for each user. The wireless unit is fully disengaged and receives pressure information from the transmitter on the back plate and calculates the remaining service time. Some makes and variations have motion detector and alarm signals that are also available.
Heads Up Displays (H.U.D.)
Using a non-distracting LED display at the perimeter of your field of vision, the HUD lets you monitor your air supply while keeping your hands free. The wireless HUD provides pressure status and alarm information. It is easily attached to the inside of your face mask.
When entering any area that demands the use of any form of Breathing Apparatus it is imperative that a risk assessment is carried out by competent people. Whilst carrying out the task it is also a requirement to continuously assess the risk that may arise, and to have a rescue plan. According to Regulation 5 of the Confined Space regulations it is a requirement to have a rescue plan prior to entering the area. The rescue plan must consist of naming the rescue team and to ensure rescue is timely.
When choosing our Breathing Apparatus we must know the limitations of the equipment that we are using. We must also be aware that as a competent person dictates that we must know how to inspect, don, wear and use the equipment correctly. Also under the Provision and Use of Work Equipment Regulations (PUWER) we must be able to inspect the equipment and to ensure we have the service record card for the equipment prior to use, to ensure all equipment is serviced in accordance with the Manufacturers guidelines. Commonly we would service the equipment annually. However this may also be led by your organisation. Some company policies will prefer to service more regularly.
Common safety standards
EN 136 Respiratory protective devices; Full face masks
EN 137 Respiratory protective devices; self contained open-circuit compressed air breathing apparatus
EN 138 Respiratory protective devices; Fresh air hose breathing apparatus for use with full face mask, half mask or mouth piece assembly EN139 Respiratory protective devices; Compressed airline breathing apparatus for use with a full face mask, a half mask or a mouthpiece assembly
EN 144 Respiratory protective devices; Gas cylinder valves
EN 148 Respiratory protective devices; Threads for face pieces
EN 12021Respiratory protective devices; Compressed air for breathing apparatus EN 1835 Respiratory protective devices; Light duty compressed airline breathing apparatus incorporating a hood or helmet
Published: 10th Jul 2009 in Health and Safety International