Find the Right Gas Detectors: Know the Basics

Introduction

For anyone who is conducting a search for a new gas detection product, the process can be overwhelming. This is due to the alternative technologies and the number of similar looking products available.

A basic search engine search brings up lots of results for many gas detection products that appear to be very similar. There are loads of gas detection products that might appear to do the same thing, but upon closer inspection of functionality, specification and features, you will notice that there are major differences in the capabilities of the products.

Looking for a product solely upon knowing which gas you need to detect is not enough!

Understand Your Site Risks

Even before you've considered researching the various types of gas detection equipment, a risk assessment needs to be conducted to give you a basis of what you're faced with.

A gas hazard can be found in three forms; oxygen depletion, toxicity, and explosive gases.

1. Oxygen Depletion can occur where there is potential for high concentrations of gas other than ambient air. Even non-explosive or non-toxic gas can displace enough ambient air to reduce the oxygen level to a level where is it unsafe for an operator to enter. A particular risk is in areas where there are gas storage tanks housed in a confined space where access is rare but required, i.e. boiler room.

2. Toxic Gases can come in many forms, a risk assessment will identify all toxic gases that may occur, every toxic gas has an exposure limit regulated by the HSE with the EH40 document. In an area in which there is potential for toxic gases to be released into atmosphere, there should be a specific sensor to monitor that gas and should alarm before the concentration exceeds the exposure limit.

Common Misunderstanding is to use an oxygen sensor to monitor toxic gases on the assumption that it will alarm when oxygen is displaced. A typical oxygen sensor will offer a resolution to 0.1% volume. This will alarm when there is a concentration of 0.1% volume or 1,000ppm. This is not a suitable technique for toxic gas detection as many any gases are toxic in concentrations below 1,000ppm.

3. Explosive Gases are monitored using either IR (infrared) or Catalytic sensors. Many gases at the right concentration can be explosive, therefore both technologies can detect a number of explosive gases. However, they offer different sensitivities for different gases.

A risk assessment must identify all potentially explosive gases then the gas with the lowest LEL (lower explosive limit) must be selected as your target gas; this is often Methane or Pentane. Typically the fixed system should alarm at 50% of the LEL. Methane is explosive at concentrations of 5% vol. therefore the LEL should be set to 2.5% vol. which equates to 50% of its LEL.

Depending on your industry, you may have a variety of applications with diverse gas hazards. Knowing what gas/gases need to be monitored will determine which gas sensors should be installed.

However, it is important to remember that it is the end-user's ultimate responsibility to identify all potential hazards.

Identify the Primary Objective

Every site is unique and there can never be a one size fits all approach when it comes to gas detection. An employer needs to identify their prime objective because some products will have been designed to protect workers as they carry out their jobs and alert them to imminent danger whilst others are solely designed for simply data-logging. Fixed gas detection systems are installed to protect an area.

So you need to think about the purpose of the product use; does it need to alarm, what type of alarm is required, do you want to read the data locally or will it need to be transmitted to a BMS off-site or will the detector need to activate other processes on site such as ventilation systems.

Ask the Right Questions

Having identified the primary objective, suitable gas detection equipment is selected by asking a number of key questions;

  • Where are the gases detected and where might they come from?
  • Is the location accessible and what are the environmental conditions where detection is to take place?
  • How easy will it be to service the equipment?
  • Will the equipment offer the functionality we need? How will we power it?
Identify Where Gases are Detected and Where They May Come From

The gases to be detected should be identified by the risk assessment, however, experienced gas detection equipment suppliers are often able to assist end-users in this process, based on their experience of similar applications.

Are there several areas of concern in the workplace?

Will the risk area change, therefore is fixed gas detection suitable or would it be best to deploy transportable gas detectors?

Which gas hazards are present in each area of concern?

It is also essential to identify the potential source of a gas release as this helps determine the number and location of gas detecting sensors required for a fixed gas detection system.

 

Consider the Location & Environmental Conditions

The performance of gas detection equipment will be affected by where the gas sensor is located. Consideration must be made to factors that will affect accuracy and reliability.

Where will the gas sensor be located? Will it be on an offshore oil rig where environmental conditions (wind and rain) can affect the performance or located at an unmanned wastewater plant? Knowing the specifics about the environment, including temperature, pressure, humidity, other gases present, etc., will dictate the most appropriate sensor technology.

If gas detectors need to be used around dust or water, consider the IP rating. This detail can be found on the product datasheet.

All of these factors will have a direct bearing on the type of gas detection equipment that should be selected.

Product approvals - Does the product require certification to be used in a given application?

Understand Product Functionality

Considerations must be given to how you intend to use the equipment. Firstly, the unit will need a power source. Will this be mains supplied or battery powered? Fixed detectors are often mains powered and portable products are battery powered. Further considerations could be whether batteries are rechargeable or replaceable and how long will the charge last for. Will battery powered units have enough run time to last an entire shift?

Communications -  Will data be communicated to a BMS or SCADA? Wireless technology is growing in popularity, could this benefit you? If the apparatus is being integrated into a separate safety system, certain communication protocols may also be required such as HART® or Modbus®.

Datalogging - how much data is stored, do you need event logging? Data logging/reporting may also be required for Health and Safety records, reporting functions for regulatory compliance or insurance purposes.

Aspects like wiring configuration are important, especially when retrofitting into an existing application.

Consideration will also need to be given regarding the requirement for local displays on transmitter units and local configuration of the unit and gas displays may also be a useful addition.

Ease of Servicing the Equipment

Gas detection products need to be accessible for service engineers. For fixed gas detectors, is there enough space for the engineer to manoeuvre around the sensor and change parts. For sensors that are installed higher up because they're lighter than air, will service engineers require scaffolding, ladders or lifting gear to get close to the sensors? This type of equipment comes with a cost and needs to be considered.

Portable gas detectors could be getting used by many different people, how will you track which detectors are due calibration and how will you physically bring them in for service? Will it be more cost-effective to invest in a docking station, have them serviced on site or send them to a distributor for service and calibration?

Also, consider the frequency of service. Some gases and vapours can be detected with a number of different sensing technologies, e.g. Hydrocarbon gases with catalytic beads or IR. Catalytic beads do not provide fail-to-safety operation and therefore can require a high frequency of routine maintenance. However, IR based solutions tend to have a higher initial purchase price, but may require less routine maintenance.

How to qualify your requirement?

Firstly, we'd ask which gases need to be detected. From knowing that, this would allow us to work out the size of the product and the types of gas sensors required (for example if a client wanted to measure total VOCs, we'd consider a PID sensor. Only certain gas detectors have the capability for measuring VOCs so this dramatically would narrow the product selection).

Secondly, we'd need to know if this is a portable or fixed requirement.

Thirdly, based on points 1 and 2, we'd delve into the product functionality and environmental conditions. We'd ask about power requirements, environmental conditions, whether there's an alarm needed, is datalogging required etc.

Summary

We appreciate that this is a comprehensive list and not all aspects are relevant to all products. But by having an appreciation of the risks and workplace conditions, it will help focus your search for the right gas detector.

Some factors are useful to know when positioning gas detectors or to understand how many gas detectors are needed.

Once you've got an idea of everything that you need, contact your gas detection equipment supplier. Using their knowledge and experience, they'll be able to find the right gas detector for your requirements.

If you have questions about any of our gas detection or require help selecting the right gas detector, simply contact us