Location of Gas Detectors in Explosive Environments III

Posted by Prosense 04/06/2017 0 Comment(s)

6. Design and installation of fixed gas detection systems

The fixed gas detection system provides an early warning for the location and concentration of flammable gas accumulation under automatic or manual control and initiates the following operations.

  • Safe evacuation of buildings
  • Activation of appropriate fire-fighting and other emergency procedures
  • Elimination of danger
  • Close the transaction or facility
  • Increasing ventilation.

6.1 Positioning of detection points

Sensors are located in designated positions with information on the gas distribution and the device in use and in consultation with safety and engineering personnel.

This determination takes into account the following;

  • Combination of emission effects and release sources
  • Whether the sources of release are inside or outside the building,
  • Presence of potential risks such as door space, windows, tunnels, pits
  • Local environmental conditions,
  • Occupational health and Safety,
  • Access to the system for maintenance and maintenance of the system, including verification and verification of operation.

Sensors should be located in all areas where hazardous accumulations of gas may occur. Generally, small leaks in open areas can be distributed without causing a dangerous buildup.

In order to avoid unwanted alarms, the detection points are placed close to large potential sources of release, rather than equipment that can produce minor leaks in normal operation.

If the ambient air movement is high or the gas is released to the closed areas, the behaviour of the gas changes. The behaviour of gases after release is complex and depends on many parameters. However, information on the effect of these parameters is not sufficient to estimate the rate and extent of formation of a flammable medium in practice. This estimate can be improved by:

  • Implementing generally accepted empirical rules developed by experts on the basis of their past experience,
  • By conducting an in-situ experiment to simulate and explain the behaviour of gases. (Includes the use of smoke tube experiments, wind meter readings or more detailed techniques such as audience gas analysis.)
  • By numerical simulation of gas distribution.

6.2 Environmental conditions

Gas sensors can be exposed to many different environmental conditions. Particular attention should be paid to the selection and placement of equipment suitable for possible environmental conditions during normal and unusual use.

6.2.1 Unacceptable weather conditions

In general, unfavourable weather and outdoor conditions cause negative effects on the normal operation of the sensors. Reading problems may occur at high wind speeds. Also water vapour, heavy rain, snow, ice and dust, etc. it affects the sensors in a negative way.

6.2.2 Extreme ambient temperatures

Observe the operating temperatures of the sensors as determined by the manufacturers. In general, no gas detectors should be present on heat sources such as furnaces and boilers, and a suitable location away from the heat source should be selected.

When the ambient temperatures in the tropical and hot areas are approximately 40 ağC, the devices should be protected from direct sunlight as the temperatures will rise well above 65 ˚C.

If no other value is specified in the instrument document, the maximum specified value for performance criteria in TS EN 60079-29-1 is 55°C.

6.2.3 Vibration

If the vibration is present in the application areas, the devices to be selected should be selected in such a way that they are not affected by vibration during operation or they should be used with appropriate vibration damping equipment.

6.2.4 Using sensors in corrosive environments

Precautions should be taken to protect the sensors from damage due to exposure to corrosive environments (ammonia, acid vapour, H2S, etc.). If ammonia is present, for example, that can cause severe corrosion and electrical failures, special attention must be paid to protect the connections made from copper or brass.

6.2.5 Mechanical protection

Sensors mounted in positions that can be subject to mechanical damage should be properly protected without obstructing the free flow of air around them.

6.2.6 Electromagnetic immunity

Some gas detection systems are susceptible to external radio frequency interference caused by disturbances such as visible errors in the calibration, zero shift, and false alarm signals. In the event that such problems are expected, the entire system must be properly protected from the effects of electromagnetic interference.

6.2.7 Washing with pressurized water

The application of a mel pressurized water flushing anda process of a plant may cause gas sensors to lose their sensitivity to a great extent. Hose washing should be avoided if possible. If it is not possible to avoid hose washing, the sensors must be protected against this situation without hindering the free flow of air around them.

6.2.8 Other pollutants in air and environment

Sensors should not be exposed to airborne pollutants that may adversely affect their work. For example, materials containing silicones or other known poisons should not be used where catalytic or semiconductor sensors are present. Dusts or wet and oily sticky sprinkles, condensate drops, filters of sensors, cause loss of precision and function. This is a big risk if wet and solid materials are available to form pastes. If the use of equipment is required in such pollutant environments, it should be cleaned and maintained on a regular basis.

6.3 Access to calibration and maintenance

The sensors must be easily accessible to allow for regular calibration, maintenance and electrical safety inspection. It should be possible to mount the test equipment or all auxiliary equipment needed for these studies at the point of detection.

Sensors used for the detection of lighter gases such as methane and hydrogen are easily installed in the roof or roof forms during construction. After the installation of the facilities, it is impossible to reach the sensors, especially those placed between the roofs and other high places. These conditions should be predicted during system design and the appropriate method for calibration should be determined.