Gas Detection for Gas Pipe Networks

An Introduction to Gas Distribution

Many flammable gas hazards are present when fuel gas, typically LPG is bulk stored for distribution across a site. Such off grid applications are very common and many clients come to IGD for gas detection solutions to enhance safety in compliance with local requirements.

 The challenge:

 Clients require a system that can mix ATEX certified gas detectors with safe area and domestic gas detectors. Usually the systems must encompass, storage, distribution and use, with data transmitted to central monitoring stations. Other data may be required along with data from gas detectors. This could include totalised gas meter readings, bulk storage tank pressures, vaporiser temperature and more.

 

IGD’s Solution:

IGD are uniquely placed to help clients in this market.. IGD’s addressable gas detection solutions allow networking of up to 32 devices on a cable ‘highway’. Devices can be any mix of gas detectors, control outputs or control inputs. This allows a multiplicity of devices to be easily interfaced together to form a safety and data solution. IGD can supply control panels with one, two or eight cable highways. These can be integrated together hierarchically to build solution networks.

 A solution for a recent clients saw complete integration on one system for the following:

 

  • Tank area monitoring using ATEX addressable TOCSIN 102 Series LPG detectors
  • LPG Tank pressure and Temperature using ATEX addressable 107 Series input nodes
  • Monitoring of double containment pipework using TOC-30A Series LPG detectors
  • Monitoring at point of use using TOC-30A series LPG detectors
  • Monitoring in residences using TOC-10 Series residential LPG detectors
  • Totalising and storing gas meter data using TOC-107 series input nodes
  • Data reporting to host monitoring systems using BACNET

 

A comprehensive safety solution using modern easily deployed networked addressable systems from IGD. 

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Ethanol Detection Applied to Crop Storage

Gas monitoring plays an important role in the storage of fruit and vegetables.

During the ripening process fruit and vegetables produce, beside CO2, organic volatile compounds such as ethylene, ethanol, acetaldehyde, acetone and ethyl acetate.

Amongst the most important “ripening” indicators are ethylene, ethanol and acetaldehyde. Monitoring of these gases enables the exact control of the ripening stages and thus an accurate regulation of the oxygen and carbon dioxide content of the storage atmosphere. This can result in a reduction in cost of gas blanketing plus the enhancement of the lifetime and quality of the perishable goods.

IGD Limited can offer a number of alternatives for gas monitoring.

Tocsin 103 Series Detectors

These offer a cost effective monitoring method under T103specific circumstances. When assessing the suitability of the 103 series detector consideration must be given to the temperature and humidity specification. This type of detector is an electrochemical detector, all ethanol detectors of this type will have cross sensitivity to CO. Therefore if CO is likely to be present, typically from diesel or gas powered fork lift trucks, misleading results could occur. If it is possible to utilise this detector type then they offer the advantage of cost and long stable calibration periods. The basic detector provides a linear 4-20mA industry standard output. Addressable types are available allowing networking of detectors onto data highways thus reducing costs and increasing accuracy by eliminating analogue I/O inaccuracies.

Tocsin 102PID

The Tocsin 102PID series detectors are based on Photo-ionisation technology and offer excellent discrimination for a number of gases including Ethanol. Unlike electrochemical 102 PIDdetector types they have no cross sensitivity to other gases which could be present, in particular CO. They are also immune to contamination effects from acetaldehyde. The unit has a local display and provides a linear 4-20mA industry standard output. The units’ main disadvantage for applications monitoring a large number of points is cost and maintenance. A PID detector will require regular replacement of its UV light source.

Tocsin 700 Sampling Systems

If detectors cannot be placed directly into the area to be monitored due to climatic conditions (typical of cold stores) then a sampling system can be considered. These systems have the advantage of central monitoring using high accuracy IR detectors. T700 Sampling Such systems draw a pumped sample from the points to be monitored, sequentially. If tube runs are extended then the time to purge can be long resulting in long cycle times.

With such systems there are pumps and filters to maintain resulting in a high cost of ownership. Sampling systems should only be considered if other alternatives are not possible.

Carbon Monoxide Detection in Car Park Ventilation

Any process where there is incomplete combustion leads to the production of Carbon Monoxide. In enclosed or underground car parks this is typically from petrol and diesel engines. Carbon Monoxide is odourless and colourless, different authorities put maximum safe exposure limits at 30 to 50 ppm and even lower levels have the effect of causing drowsiness.

Having a similar density to air carbon monoxide readily mixes into the atmosphere. As the main area of concern is poisoning due to inhalation normal practice is that:

Fixed detectors need to be mounted at head or operating height. 

Carbon Monoxide has to get to a detector location to be sensed. The further the gas has to travel from its source (an exhaust pipe in this case) to the sensor the more diluted it will become. For this reason any gas detector can only really effectively cover a radius of around 6M.

Gas detectors should therefore be mounted in locations of expected poor ventilation, egress and entry points and areas where vehicles are likely to be queuing with engines idling. There is no point locating detectors on street level exit ramps or fan entries as ventilation will be good at these points. 

For more information on Carbon Monoxide Gas Detectors please visit the International Gas Detectors Ltd website.

IGD supports Gas Safety Week

What is Gas Safety Week? 

Gas Safety Week (10th-16th September 2012) aims to help raise awareness of gas safety as every year there are thousands of people in the UK alone diagnosed with Carbon Monoxide (CO) poisoning.

CO poisoning can be caused by badly fitted or poorly serviced appliances, Gas Safety Week highlights the importance of taking care or your gas appliances and ensuring they are regularly serviced.

For more information on Gas Safety Week and for tips on how to keep you and your family safe visit:

http://www.gassaferegister.co.uk/learn/gas_safety_week/whats_going_on.aspx

Why are fusible links not the answer for gas fired boiler room hazard monitoring?

The most common fuels in use for space and water heating are Oil, Natural Gas and Liquid Petroleum Gas (LPG). By far the most popular, clean and cost effective solutions are utilising Natural Gas or LPG.

The traditional safety measure derived from the time of oil fired boiler houses is the use of a fusible link placed above each boiler. The fusible link is intended to melt if it becomes overheated through a fire starting (normally through ignition of oil leaking outside the boiler). This causes an alarm to be raised and the fuel supply to be shut off.

In a boiler house where gas is the major fuel used then it is no longer appropriate to use fusible links because the hazard is very different.

If a gas leak develops there is no heat to melt the fusible link. The gas will not ignite until the lower explosive limit (LEL) of the gas is reached. At this point when the gas is ignited by a suitable source an explosion will occur causing more serious consequences.

The ignition source does not necessarily have to be a defined flame such as the boiler flame or the pilot light but sufficient energy can reside in hot surfaces or be produced through normal operation of unrelated electrical apparatus (light switch/fitting, switch panel, additional plant etc)

On dual fuel systems using oil or gas it is seen that both fusible link and gas detection are necessary safety precautions.

Why Gas Detection?

The main purpose for a gas detection system is to raise an alarm when a leak develops. The gas detection system is reading gas levels in its immediate area and by monitoring from zero gas to the LEL allows alarm points to be activated before an explosive level of gas has built up.

As most boiler houses and plant rooms are unmanned or visited at irregular intervals this allows the environment to be monitored and for any potential leaks to be detected that could otherwise go undetected for a long time.

A benefit of the detection system is its ability to provide an opportunity to deal with the leak before the level of gas has reached a dangerous level. Alarm levels allow relays to be activated and slam shut valves can operate isolating the leak from the gas source. This removes the continuation of the risk and as a further benefit will reduce fuel gas wastage and cost.

Methods of Gas Detection?

The low-cost sensing device for gas detection of flammable gas leakage is based on the semi conductor sensor.

The semi conductor detector can proficiently detect flammable gas however the major concern is its unfortunate trait that it will also detect many other gases and vapours within an atmosphere and will even provide false gas readings through variations in temperature and humidity.

The traditional low-cost sensing system is using catalytic gas detectors. These devices actually use a burning principle to detect gas and are thus immune from the sensitivity issues of semi conductors mentioned previously. The catalytic burning effect only responds to flammable gases and is a controlled reaction of what the detection system is there to prevent and consequently takes all atmospheric effects into account without further sophisticated electronics. The technique is quick and has been utilised for over 90 years. The robust nature of the sensor housing and its uncomplicated connection makes them very simple devices to install, commission and service.

The most expensive solution is to utilise Infra-red absorption as the method of detection which responds quickly and can be more sensitive than catalytic detectors. Internal within the detector is a beam of Infra-red radiation that passes from a source to a detector. The detector will show if there is any loss of energy between source and detector. The size of this loss is a measure of the amount of gas along the path of the beam.

This detection system can derive speed and accuracy benefits but unfortunately carries a high price level and can derive a more extensive and expensive maintenance regime.

Location of Sensors and Control Equipment

The first consideration is placing the control panel. Normally this is located outside of the area of detection allowing people to view the alarm situation without endangering themselves. This may be just outside the Boiler Room or in a normally manned area like a Reception Area or Security Lodge.

It is then dependant on the nature of the gas being consumed that determines the placement of gas detectors.

Natural gas (which is largely methane) is lighter than air and therefore upon release will predominately rise towards the highest point in the boiler room.

In a lot of cases boiler houses and plant room ceilings are a network of pipe work and ducts and it is common to place the detectors at a lower level over the leak source utilising a collecting cone to enhance gas gathering to the sensor.

LPG is heavier than air and therefore upon release will tend to fall to the floor and follow any sloped and drains in the surface. It is recommended that these detectors are placed 6-18″ (15 to 45cm) from floor level and a splashguard is utilised to prevent accidental water ingress.

The most likely points in the gas installation for leaks to occur are:

  • The gas meter
  • The mechanical shut off valve (if fitted)
  • The solenoid shut-off valve
  • The pressure booster if fitted
  • The gas train
  • The gas burner

As a general rule it is common to utilise a 4 meter radius of detection for gas detectors. In a small boiler room all the above points can be close enough that only one sensor will be needed. On installations of one or more large boilers as in hospitals, factories or large blocks of flats it may be necessary to fit one sensor at each of the above points.

System Outputs

Sensors are usually wired individually to a control panel, which will give a visual indication that preset alarm levels have been reached.

On installations with a number of sensors it may be cost effective to install an addressable  system which enables sensors to be wired via a single highway cable providing savings in material and labour.

For both system types when a present alarm level is exceeded, alarm relays change state to begin any required action, by means of volt free contacts.

In practice a lower alarm relay normally activates audio/visual alarms:

  1. Outside the entrance to the boiler house
  2. Site Reception Area
  3. A remote site such as a security gatehouse/caretaker’s office

The higher level contact may cause the gas supply to be shut off and raise an alarm to evacuate the area.

Alternatively these alarms may be fed through to a Building Management System (BMS) for integration to the sites overall management tool.

 

Further Considerations

Oil Fired Boiler Systems are not immune from gas detection requirements as many of the oil fired systems rely on LPG to provide the initial firing of the burners. Once the Oil is alight then the LPG is withdrawn.

Be aware that as stated earlier LPG is heavier than air and will fall upon release requiring sensor locations closer to the floor.

On dual fuel systems using oil or gas it is seen that both fusible link and gas detection are necessary safety precautions.

 

Ventilation operation savings with Gas Detection

With the ever-increasing costs of energy and Building Owners seeking to find efficiencies, ventilation has become a key area for energy management. More site owners and facility management companies are looking at the impact of the ventilation power budget and the previous behaviour of constantly running the ventilation package is no longer consistent with today’s economic environment. With human intervention not practical, some form of automatic operation that does not compromise client safety or comfort must be utilised.

International Gas Detectors Ltd offers the TOC-20 Series Gas Detectors which are designed to provide an accurate measurement of CO2, temperature and humidity into a variety of ambient monitoring applications, allowing you to monitor the ventilation rate and assess what rate is required for the given environment. This gives the opportunity to save energy by cutting out any unnecessary ventilation. Using the latest microprocessor technology and software the TOC-20 is a reliable long term monitoring solution which is easily integrated into existing or newly planned control systems. The TOC-20 is supplied pre-calibrated ready to use. 

TOC-20 Series Gas Detectors