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Topic Title: Hazardous areas
Topic Summary: Boilerhouse?
Created On: 18 August 2012 01:25 PM
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 18 August 2012 01:25 PM
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If a boilerhouse with a gas fired boiler has gas leak detection linked to an automatic gas shutdown valve, is hazardous area classification still required?
 18 August 2012 02:11 PM
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Quite possibly, there will be many factors affecting your answer and a definative answer can only be given by having sufficient details of the installation. Some things to think about....

The gas detection and shutdown systems will have to be ATEX approved anyway.

If your fuel lines to your boiler have flanges then there will be a hazardous zone around those hte size dependant upon the fuel type, pressure and pipe bore. You may be able to reduce the hazardous area with protection sleeves.

The problem will then arise if any flanges etc are within an enclosed area as you will need a ventilation system to ensure that any escaped gas is removed from the space. There may be a need for that ventilation system to also be ATEX approved.

Kind regards

Donald Lane
 18 August 2012 03:01 PM
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Thanks Donald,

I'm still unclear though - an answer on the HSE website to a very similar question:

Low pressure pipelines carrying mains gas to gas burning equipment have not traditionally been considered as sources of hazardous leaks, and area classification has not been applied in such circumstances. Boiler houses are normally well ventilated, but the ventilation has usually been designed to provide air for combustion and to control room temperatures, rather than help disperse small leaks. The security of gas pipework operating at any pressure should at least be considered in any risk assessment made under DSEAR. Pipework is most likely to be reliably gas tight if:
it has been installed to a recognised relevant code
it has been properly maintained, including periodic pressure testing or leakage testing from the joints, and
there are no external influences likely to cause early failure, eg by corrosion, impact or vibration

There is ongoing work to assess the size of any potentially explosive gas cloud which may be expected to form, arising from the combination of the range of mains gas pressures and holes of specified sizes in such pipework. This is likely to be published by the Institution of Gas Engineers and Managers in due course.
Burner control packages mounted on the face of a boiler are often very close to hot surfaces, or air intakes that are directly connected to the internal flames. In these circumstances, it makes little sense to assign a hazardous area around the gas fittings or use ATEX-compliant electrical parts so close to other permanent sources of ignition. It is appropriate to design the pipework and gas control train to minimise the risk of a leak.
 18 August 2012 05:03 PM
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Well in my opinion it is going to boil down to a risk assessment based upon the installation you have and the information you have found out, it should be easy enough to work through. here are some starters.....

Identify the pressure of the system, higher pressures offer more risk, lower pressures less risk as the HSE have implied.

What is the pipeline construction? Flanged joints with gaskets offer more likelihood of a leak than screwed or welded joints.

How is the pipe installed? A pipe run along at floor level may be easier to damage than a pipe that is run overhead.

Do you have installation and maintenance records for the pipework? Initial installation and test records can be used as a mitigation against leaks as do periodic maintenance records and the results of leak testing. If you have none of this you are operating at a higher risk.

You mentioned a leak detection system. Are there regular maintenance and calibration checks carried out and do you have the records? Is it maintained accoring to the manufacturer's recommendations? Use of calibrated sample gases etc.

Where are the sample tubes for the leak detection system? If they are in the areas where there are likely to be leaks then the likelihood of detection is higher and your risk lower. If the samples are taken from general areas in the roof space then your detection rate may be lower.

How does the leak detection system operate? Alarms first and then trip, is it fail safe, does it trip if power is lost to the system? Does it alarm back to a remote control room? These can all reduce risk.

How old is the system? Is there previous history of leaks? Where is it installed, is it in a remote area with a low likelihood of people being around it. I used to have a boiler sited undereath a control room that was manned 24 seven. That puts it up a risk category.

What aspects of the electrical system are you concerned about that may need to be ATEX approved. As the HSE have pointed out what is the point of ATEX compliant boiler controls when they are attached in close vicinity to the boiler with hot surfaces that can ignite the gas. Is there a sample tube for the detection system near to the electrics?

If it is general electrics you are concerned about such as lighting and sockets can they be moved? What is the realistic likelihood of a gas leak getting near those electrics? If the fuel gas is lighter than air and the pipework is all at height then would a leak get near sockets mounted on a wall?

Go back to the ventilation of the boiler house. If there are roof mounted vents then the gas is more likely to disperse outside naturally. if it is a forced ventilation system does it alarm if it fails?

...and so on.

Just build up a table of the risks and how they are controlled and you should be able to come to a conclusion as to what will need ATEX compliance and what doesn't.

Hope the above helps.

Kind regards

 19 August 2012 01:56 PM
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 21 August 2012 10:39 AM
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It it is any consolation, some of us out here are not sure either - and
dlane has given you a good insight into the mechanisms.........

Our client has a boilerhouse with gas boosters sited ajacent.
The gas boosters are external and zoned.

After a Hazop study they decided to attempt to define Zoned areas inside the boilerhouse starting with flanged areas of the gas piping but then 'fell over' the flame arrestor. Upon finding the flame arrestor to be ATEX rated (no I did not believe it and never saw supporting documentation), they could not work out how to zone the area round the flame arrestor which in any case was close to a non rated boiler and burner ass'y. On the upstrean side of the gas main was an ATEX rated Mass Gas Flowmeter but not wired with intrinsic safety in mind.

The building ventilation had just been refurbished and relied on both forced ventilation at floor level and natural venting in the roof voids.

It was not surprising to find the subject quietly dropped.
 23 August 2012 11:08 AM
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I agree with previous commentators about the uncertainty of ATEX & boilerhouse. However natural gas leak detection is not expensive to purchase & install. We use sensors manufactured by NTRON & have found them to be reliable. One thing to look out for is that the fuel gas & the igniter gas can be at different pressures & can also be chemically different (propane from bottles ??). You will have to cater for both in your detection scheme.
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