Properties of natural Gas:
* Nontoxic – Contains no poisonous toxic ingredients.
* Lighter than Air – rapid dissipation.
* Colourless – One of the cleanest burning fuels producing heat, CO2 and water vapour.
* Odourless – A harmless but pungent odour is added as a safety precaution.
* Narrow combustion limits – The gas will only ignite when mixed with oxygen, less than 5% or more than 15% will not ignite.
* Environmentally friendly – When natural gas burns it creates virtually no harmful emissions.
* Highly Flammable – When the gas is combined with oxygen at the right might as above it is a highly flammable substance.
* Excess Pressure
* High Temperature
* Carbon Monoxide Poisoning
When a gas is liquefied, the pressure can increase rapidly as the temperature rises. Under normal conditions, a relief valve on the storage cylinder will release gas to prevent the cylinder from exploding due to over pressurization. When a cylinder or valve is not properly maintained and rapid pressure build-up occurs due to exposure to fire or other sources of extreme heat, a cylinder failure and subsequent explosion can occur.
The safest way to transport natural gas is through pipelines made of steel, however most distribution lines from the main line to the customer have been made out of plastic since the 1980’s as they are easy to lay and do not corrode.
As natural; gas is compressed for storage and transportation, its relative pressure increases. The systems used to supply gas to the end user must be completely sealed with additional safety measure built in to accommodate for these pressure changes.
There is a danger that any pipe work may not have been installed correctly which can lead to leakage which may lead to fire or explosion. Damage to pipe work can cause immediate leakage or leakage which can occur some time later due to inadequately supported pipes or fittings.
Temperature can heavily influence the pressure inside any pipework, through expansion high temperatures can cause the gas to expand inside of the pipework. The pipework may fail due to the increased pressure and lack of sufficient control over the system.
Every year people die from carbon monoxide (CO) poisoning caused by gas appliances and flues which have not been properly installed or maintained. Many others also suffer ill health. When gas does not burn properly, as with other fuels such as coal, wood or oil, excess CO is produced which is poisonous. You can’t see it, taste it or smell it but CO can kill without warning in just a matter of hours.
Gas Service technology 1
Six-year-old Elisabeth Giauque was living with her family in a rented house in Castle Close, Wimbledon. On 4 February 2005 her parents went out for the evening, leaving their three children in the care of the nanny. On their return they found Elizabeth unconscious in her bedroom. She was rushed to hospital where she died two days later. It was later established that she died from carbon monoxide poisoning.
Bill Hazleton HSE Inspector said: “This tragic case emphasises the importance of maintaining and checking gas appliances. Carbon Monoxide gas is a silent killer, you cannot smell or see it. Landlords have a duty to maintain their gas appliances, and it is illegal and highly dangerous not to have them checked yearly by a competent, registered gas fitter. Currently, only CORGI is recognised by HSE to register gas installer.”
As gas is highly combustible there is an increased danger of explosion upon ignition. Most dwellings contain boilers and gas burning appliances which if not maintained or left on can fill a room with gas, if this gas ignites an explosion may occur which can seriously injure any occupants and cause fatality.
Asphyxiation/suffocation may occur due to poorly ventilated spaces being filled with gas. If a fuel burning appliance is left on over night unignited the gas will begin to fill the room. As gas is lighter than oxygen it will tend to rise and dissipate into the atmosphere, however if the gas is filling a room which is poorly ventilated it will displace the oxygen putting the sleeping occupant at risk from asphyxiation.
Performance Requirements of a single stack Drainage System in a Two Storey Dwelling
The Majority of Single Stack systems are manufactured using PVC to ensure continuity and universal fittings. Part H of the building regulations sets out the design requirements for stack systems, all systems should comply with these regulations.
There are four primary single stack systems which are listed in BS EN 12056:2:200, they are all similar in design with the main difference being Ventilated/Unventilated general performance requirements for all four systems are generally the same principle.
A single stack system in a two storey dwelling should:
* Covey the flow of foul water to a foul water outfall.
* Minimise the risk of blockage or leakage.
* Prevent foul air from the drainage system from entering the building.
* Be easily accessible for cleaning etc.
* Not increase the vulnerability of the building to flooding.
* Cope with pressures inside of the system.
* Have a large enough capacity to carry the expected flow at any point.
* Be capable of withstanding an air test of positive pressure of at least 38mm water gauge for at least 3 minutes.
* Every water trap should maintain a water seal of at least 25mm.
The trap is a device which is designed to prevent the passage of foul air by means of water seal. The depth of water which would have to be removed before gasses and odours could pass through the trap is shown as H in figure 2.
Figure 2 – Water Depth in Trap
Figure 3 – Typical Vented Branch EN BS 12056:2:2000.
Pneumatic Cold Water Systems in High Rise Buildings
To supply water to high rise buildings the head of water in the main needs to be sufficient.
The head of water in the mains can be calculated using the following formula
p = r x g x h
Rearranging gives; h = p / ( r x g )
p = Water pressure (N/m2 or Pa) To convert from bar pressure
– 1 bar = 100,000 N/m2 or Pa.
r = Density of water (1000 kg/m3
g = Acceleration due to gravity ( 9.81 m/s2)
h = Head (m)
For water pressure of 3.4 bar the equivalent head would be;
h = p / ( r x g )
h = 3.4 x 100,000 / ( 1000 x 9.8 )
h = 34.66 metres
In this instance the water main will be capable of delivering water to a height of 34.66m, however there would be no flow of water from a pipe at this height and pipe and fitting resistance will need to be considered. To overcome the problem of flowing water at height a pressurised system can be introduced to boost the pressure thus increasing the maximum distribution height.
A pressurised system can overcome the problems of delivery rate and pressure through a number of controlled units. The water will start at the mains and then travel through a series of pipes where it will then pass through a non return valve to prevent possible contamination. The pathway is then split into two directions; the water will pass through another valve to supply the lower levels of the building with water which is adequately pressurised straight from the main.
The second path will take the water through a pumping system and further non return valves, the pumps will force the water into a pressure vessel which is higher than the highest connection in the system, this pressurised drinking water is then fed to the remaining upper levels. At the top of the building there is a cold water storage tank which is fed also by the pressure vessel, this tank is used for non drinking water and gravity is used to pull the water from the system.
The following diagram outlines a basic pressurised sytem which is commonly used in multi-storey buildings throughout the uk.
Disposal of domestic waste within a typical high rise domestic building
Waste management is now at the forefront of construction planning with the building regulations recognising the importance of recycling. Typically in high rise domestic buildings the majority of recyclable waste is bundled with general waste and sent down one primary chute which fills a large bin at the bas of the building. The problems associated with chutes are generally ones of fire risk and blockage hazard.
Recycling chutes are currently being installed throughout high rise buildings in London and proving successful. Westminster city council is one of many local authorities to convert a general refuse chute to offer recyclable opportunities. Councillor Alan Bradley, Cabinet stated “A typical family in Westminster produces 0.5 tonnes of waste a year, and half of that is recyclable, so to make a difference it became apparent that we would have to find way to make it easier for people in flats to recycle.” Following the implementation of the scheme recycling within the estate has more than tripled.