Frequently Asked Questions
(Topics not covered under fibreflow System / How does it work)
Some of the questions we are asked during training programs:
-
How old is blown fibre?
-
Am I limited with Blown Fibre to 4 or 8 fibres per microduct?
-
Is it necessary to test a blow route before blowing?
-
How do I decide where my blow points should be?
-
Is there a way to achieve a very long single blow length (eg down a non-access tunnel)
-
Do trenches have to be very straight for blown fibre?
-
Will I be able to blow vertically up a tall building?
-
Can a route be checked for leaks?
-
At high elevation (above sea level), will the air supply be adequate?
-
Can I use ANY compressor to blow fibre?
-
What do you mean by 'conditioned air'?
-
What are the fibreflow temperature limits?
-
Will temperature changes cause the fibre unit to expand and contract?
-
In a waterlogged manhole, how do I keep the microducts dry?
-
What if caps were omitted and water has got into the microducts?
-
Does water immersion affect the optical properties of the fibre?
-
Why is Low Fire Hazard material so important for indoor networks?
-
Halogens are flame-retardant, so why go halogen-free?
-
What fire test specifications do the LFH products meet?
-
Aren't there new European fire regulations for indoor cables?
-
Is there an International Standard for these products?
We have many years experience of installation by blowing.
If you do not find the topic you seek, please let us know.
Q1: How Old is Blown Fibre?
There are some fibre installers who have still not come across blown fibre, and yet it is now regarded as very well established technology, with international standards being published.
British Telecom (BT) first attempted to blow ‘basic simple fibre constructions’ into microducts around 1980 and soon learned how to increase the success of getting fibre into a 500m length of microduct, sufficient for access networks at the time.
They developed the first blowing head and later improved its design by incorporating buckle detection and changeable plates. They worked on improved fibre unit design, making it smaller and more flexible. They spent time defining the air dryness conditions that favour blowing, and made improvements to compressors to provide such air as standard.
Since then Emtelle have also made many innovations to the technology:
-
Direct Buried types
-
19-way, 12-way and 24-way
-
New fibre units
-
Improved microducts
-
Combinations of microduct sizes in one assembly
-
Combinations of blow microducts and copper cable
-
Termite-resistant types
-
Overhead types
-
Purpose-designed closures and accessories
LINK
In all, the techniques of fibre blowing have been well developed, and are now so established that fibre blowing is becoming the most popular way to install fibre into the access network.We estimate that over 300,000 kms of Fibreflow has now been deployed around the world. It is not new technology.
Early design blown fibre microducts in an early closure
Q2: Am I limited with Blown Fibre to 4 or 8 fibres per microduct?
NO.
The smaller microducts, up to 8mm OD are designed for FIBRE UNITS. These are single items incorporating up to 12 fibres.
But we also offer fibre MINI-CABLES, which are lightweight cables with higher fibre counts, right up to 96 fibres in one cable. These can blown into our larger microducts, 10mm and 12mm, or even bigger if necessary.
But remember that the bigger the fibre bundle, ie the heavier it is, the bigger the microduct needed to accommodate it, and also the blowing distance will be less. So it is often expedient to select the fibre count to balance both tube bundle size and blowing distance.
Route Topics
Q3: Is it necessary to test a blow route before blowing?
A: Our microduct is tested for ‘continuity’ when made, so we do not expect manufacturing blockages. On the route we recommend an airflow check, which confirms a) absence of leaks, b) absence of crush/blockages. A dart may be blown through if desired, but is not normal practice.
Q4: How do I decide where my blow points should be?
A: These matters are covered in the training. Or we can put you in touch with our registered installers around the world. We also provide network planning advice.
Q5: Is there a way to achieve a very long single blow length? (eg. down a non-access tunnel)
A: Yes. Use:
Greater microduct size
Higher air pressure
Smaller fibre unit
Reduced bends (straighter route)
Q6: Do trenches have to be very straight for blown fibre?
A: No, just reasonably straight. The straightest routes do blow best, but the DB design tends to lie fairly straight in any case. It is wise to have a fairly flat trench bottom, so the cables retain their straightness during earth re-compaction.
Q7: Will I be able to blow vertically up a tall building?
A: Yes. Fibre units have very low weight, unlike traditional fibre cables, and we have blown all fibre units to the top of many very high blocks (35+ floors).
See also The Far End
Air Topics
Q8: Can a route be checked for leaks?
A: The tolerances on the fibreflow microducts and connectors should ensure a good seal at every joint. If an installer has failed to make a good connection, this may become evident when the air flow is measured. Fit the airflow meter on the ‘far end’ of the route, then check the litres per minute arriving. An abnormally low airflow indicates leakage at some point, so check the connections along the way.
Q9: At high elevation (above sea level) will the air supply be adequate?
A: It is true that lower air pressure at altitude reduces the volume of air through the compressor, but normally there will still be sufficient for blowing.
Q10: Can I use any compressor to blow fibre?
A: Not usually. The best blowing performance relies on the air supply not adding moisture to the tube route. The Emtelle compressors deliver 'conditioned' air which achieves this.
Q11: What do you mean by 'conditioned' air?
A: When air is compressed, say to 10bar pressure, the water held in it cannot be compressed and some of it drops out. But the compressed air is still saturated (100%RH) and also warmed up: perfect to create condensation! So we add devices after the compressor to reduce this high moisture content to just the right level. So it enters the tube under pressure, and does not become too wet or too dry as it makes its way, expanding and accelerating, to the tube exit.
Temperature Limits
Q12: What are the Fibreflow temperature limits?
A: The majority of fibreflow networks are exposed to temperatures between zero and +40°C. This is a comfortable range.
However, the microducts and fibre products may also be stored and used at temperatures outside this range.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
*Temperatures above these may be tolerated for short periods. Please consult Emtelle.
Q13: Will temperature changes cause the fibre unit to expand and contract?
A: Optical fibres have extremely low thermal expansion, so it is the cables or microducts that are more likely to experience any expansion or contraction.
In fact for underground routes, the cables, microducts and fibres hardly see any temperature changes at all. There will be some local heating/cooling at exposed positions, but each FU in its low friction microduct has free longitudinal movement, so can absorb the small change by free movement in a much longer tube length.
Fibre trays also have provision for some fibre movement.
Our fibreflow PE has excellent sub-zero properties.
Water Contact
Q14: In a waterlogged manhole, how do I keep the microducts dry?
A: Microduct caps are available to stop water getting into the microducts. Cables are delivered with full end caps in place over the sheath. Do not cut them off until microduct access is needed.
Q15: What if caps were omitted and water has got into the microducts?
A: You can blow the water out again from the other end. Normally it will be a small amount. If long lengths of microduct are flooded, it is better to blow a cleaning dart through first. Remember also that the normal blowing process removes the resident air and introduces ‘correct’ air.
Q16: Does water immersion affect the optical performance of the fibre?
A: The fibreflow system is designed to prevent large scale water ingress. However the fibre package is designed and tested to withstand accidental water immersion for very long periods.
Our product is regularly subject to a 2000 hour test in water and does not experience any significant change in properties (optical or otherwise) during test.
A wet day in the access network
Fire Testing
Q17: Why is LFH material so important for indoor networks?
A: It is all based on improving your chances of escape from a burning building. Dense smoke prevents you from finding the exit. Fumes incapacitate your body. Highly flammable materials spread the fire and increase its intensity.
LFH products greatly reduce all these hazards, and make escape more likely. If you were to witness the fire tests we perform, you would need no persuading to use our LFH range. The performance would speak for itself.
Typical fire 'flashover' in a building.
This is when items heated in an enclosed space
but not in contact with the flame, ignite suddenly,
making the fire an impassable barrier.
This scenario can develop in just over 3 minutes
from fire onset. So prompt escape from the area is vital.
And anything that helps make indoor items more
resistant to this eventuality has to be good.
* Link to smoke test photos
Low Fire Hazard (LFH) does not just mean 'Low-Flam', or 'Low-smoke', or 'Halogen-free', but all of these:
LOW flammability / ignition
LOW smoke density
LOW levels of fume, gas and acid
Q18: Halogens are flame retardant, so why go halogen-free?
A: It is true that PVC and other halogenated plastics resist ignition, but in full-scale fires this makes little difference, decomposition being inevitable, and the toxic gases and high levels of smoke produced are considered undesirable in most current cable specifications. Much less toxic and 'low-smoke' alternatives are now available and are replacing halogens in most cases.
Q19: What fire test specifications do the LFH products meet?
A: The fibreflow LFH range fire performance exceeds most In-building
fire regulations.
We take fire performance seriously and use excellent materials.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Q20. Aren't there new European fire regulations for indoor cables?
The details are still approaching final agreement (which also means changes are not ruled out!) :
Vertical fire performance will be tested to EN 50399 on a rig not unlike the 60332-3 vertical ladder. Flame spread, heat release and smoke will all be measured. This grade is fine for most applications.
More severe fire situations will require cables to meet tighter 50399 limits.
Emtelle will tie-in with these regulations when they are introduced.
Q21. Is there an International Standard for blown fibre products?
A:
The benefits of blown fibre are rapidly becoming more widely accepted across the world.
Consequently, a new International Standard for blown fibre has been written and is now published.
It is called:
"
The test methods referenced are from IEC 60794-1-2, common to the fibre optic cable industry, and are internationally recognised. Emtelle support these test methods fully and have been using and quoting them long before IEC 60794-5 was drafted.
