4 Steps To Selecting A Fixed Gas Detection System

Selecting the right gas detection solution is crucial for the safety and protection of your plant.

In many applications, fixed gas detection systems play a major role in protection; this post will share four steps to selecting a fixed gas detection system.

What is the fixed gas detection system?

A fixed gas detection system is permanently installed on-location and continuously monitors environments.

Fixed detectors work similarly to fire and smoke alarms. Detectors specific to a target gas are deployed on-site and connected to a control panel.

4 Steps To Selecting A Fixed Gas Detection System

These are the four steps to selecting a fixed gas detection system. If you follow them, you will have a system that meets your needs and can position the sensors optimally.

Step 1: Define the problem

You need to evaluate your plant and figure out what problem you are trying to solve. Here are the main questions you should ask yourself.

Which gases need to be detected, and at what range?

List the gas or gases you need to detect (the “target” gas or gases) and the ranges in which you need to detect them.

What is the reason for detecting these gases?

Is it to prevent an explosion? To prevent asphyxiation? To prevent employee exposure to potentially toxic gases or vapors? To control a process?

What gas levels do you wish to take action, and what action is needed?

Step 2: Define the area to be monitored

The area to be monitored is very important. You need to study it and answer a few questions carefully. Is the area outdoors or indoors? Is there oxygen in the area, or is it an inert environment?

What is the classification of the area? Do the sensors need to be explosion-proof? Intrinsically safe? Weather

resistant? Corrosion resistant?

Answering these questions will help you find the right sensors that will be able to work on your project without any issues.

Imagine spending a lot of money buying sensors and, ultimately, figuring out that they will not work in your project because those sensors will not work in an inert environment.

Step 3: Define the area where the controller will be installed and what action the controller must take

One of the main components of a fixed gas detection system is the controller. This will be the brain of your system.

Before you buy the controller, you need to ask yourself a few questions. Is there any plan to expand the system? How many sensors can the controller take? What actions do you want the controller to take? And do you want to integrate the controller into an even larger system?

For example, if I want a gas detection system connected to a Building Management System (BMS) and the BMS uses BacNet, I will want a controller to have a BacNet output.

Step 4: Decide how many sensors do you need

You need to estimate the number of fixed sensors you need. This is not a straightforward process, but I will share how I determine the number of sensors needed in a project.

How to determine the number of sensors needed and sensor placement

Please consider the guidelines below and draw your proposed sensor locations on the Applications

How much area can one sensor cover?

Consider that a sensor operates similarly to a person’s nose. A nose can only sense what is immediately surrounding it.

If there is a rotten egg 10 feet away, but with a strong wind blowing the smell away from you, you may not smell the rotten egg, or at least not smell it very strongly.

On the other hand, if you are downwind of the rotten egg, even 100 feet away, you likely will smell it. If you

are indoors with rotten eggs, the vapors can travel quite a distance to cover the entire room.

Depending on ventilation patterns, the smell may be worse in some areas. Gases behave much the same as the rotten egg odor.

The key is to locate the sensors as close as possible to the likely leak source or sources.

If the gas could come from almost anywhere in a building, such as for CO monitoring in a parking garage, then sensors must be spread throughout the garage to get full coverage.

In another example, if you are monitoring a 100’ by 100’ room for flammables, but the only possible source of flammables is a tank in one corner, then it is necessary to monitor the tank in the corner but not necessarily other areas of the room.

Sensor spacing for indoor applications

For applications where the gases could exist anywhere in the facility, a decision must be made on how far apart to place the sensors and how many sensors should be used.

There is no fixed answer to whether this is correct for all applications, but an industry guideline is to space the sensors approximately 40 to 50 feet apart for indoor applications.

Sensor spacing for outdoor applications

Outdoor applications will be very susceptible to wind conditions, and good coverage of a point source leak, such as a propane tank or valves, cannot be done with just one sensor.

If the tank or valves cannot be enclosed or shrouded somehow, sensors should be placed as close as possible to the possible leak source, and multiple sensors should be used to provide good coverage for all typical wind directions.

Other considerations or guidelines

In deciding sensor count and location, please consider the following:

Locate the sensor near the possible leak

Locate sensors strategically in the most likely path of a gas leak. Carefully evaluate possible leak sources and ventilation flow of the area to be monitored.

Consider the relative density of the gas.

Gases that are lighter than air will rise, so sensors for these should be located near the ceiling (one foot from the ceiling).

Heavier than air gases or vapors, they will tend to remain near the floor, so sensors for these should be located near the floor (one foot from the floor).

Consider the Flash Point of the gas to be detected

Consider that flammable substances with high flash points (higher than normal room temperature of 60 to 70 degrees F) will not have much vapor if the surrounding area is cold.

Liquids with high flash points cannot produce an explosive level of vapor at cold temperatures unless they are heated.

Sensors must be located as close as possible to the leak source of these liquids to detect them.

Consider the temperature of the area to be monitored

Gas detection sensors have certain temperature limits that cannot be exceeded. If the area is too hot for the sensor, you should consider using a sample drawing-type sensor to allow the sample to cool before exposure.

Suppose the monitored hot vapors have a flash point temperature higher than the ambient conditions.

In that case, the sample cannot be cooled below this, or condensation of the vapors will occur in the sample tubing. 

Please consult the sensor manufacturer for another solution, such as a heated sampling system or device.

Wet areas

If the area is wet, please select sensors (and controllers) for wet areas. Install sensors facing downward so they can shed water or rain.

If using a sample draw system, install appropriate water traps or hydrophobic filters.

If possible, install detectors where exposure to splashing will be minimized.

If monitoring a trench that could periodically get filled with water, mount the detector high enough so it cannot get flooded. If this is impossible, consider using a sample draw head with a floating sample inlet.

Vibration

Install detectors that will be free from vibration. Heavy or constant vibration can shorten the life of a sensor.

Dust or dirty areas

If the area to be monitored is especially dirty or dusty, select sensors or filters to prevent the dust or dirt from clogging the sensor.

Maintenance

When selecting sensor locations, remember that sensors must be accessible for maintenance. Do not install in difficult-to-reach areas.

If this is not possible, consider using a sample draw detector head so that the sample tube is only run to the inaccessible area and the sensor is easily accessible.

Consider the location of the workers.

Consider the location of the workers and the source of the toxic gases when locating toxic gas sensors to protect workers. The sensors should be located between these two to warn early about rising gas levels.

Physical protection

Do not install sensors where they may be physically hit or abused.

Key Takeaways: Selecting a fixed gas detection system

4 Steps To Selecting A Fixed Gas Detection System

  • Step 1: Define the problem.
  • Which gases need to be detected, and at what range?
  • What is the reason for detecting these gases?
  • Step 2: Define the area to be monitored.
  • Step 3: Define the area where the controller will be installed and what action the controller must take.
  • Step 4: Decide how many sensors do you need.

Thank you for reading

 

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