Very broadly gas detectors fall into two broad categories, fixed or portable. Both types use a variety of sensor technologies to detect gas or vapour hazards. Both types have their own strengths and weaknesses and subcategories. Therefore, it is extremely important to understand the nature of the gas or vapour hazard you are trying to mitigate to determine the most appropriate detection solution. A risk assessment will always be the starting point. Mitigation will take a few forms – gas detection being one of them. At that point it is usually best practice to involve gas detection companies to find suitable solutions.
In this article, we will give a brief overview of the application of fixed and portable gas detectors. The intention is not to discuss individual sensor technologies but to provide some background knowledge we feel is important when considering proposed solutions.
Fixed Gas Detectors
Permanently installed on-location, fixed gas detectors are used to continuously monitor environments. Fixed detectors work in a similar manner to fire and smoke alarms. Detectors specific to a target gas are deployed on site which are connected to a control panel. The controller monitors the detectors and sets alarm conditions based on gas levels. At a basic level audible and visual alarms are triggered to alert personnel. More advanced installations may alert other monitoring systems, activate shut down systems, log and trend data, connect to cloud-based systems and more. This is one of the main benefits of fixed over portable gas detectors.
Fixed detectors will monitor a limited area/volume around the detector, typically a 5M radius. This means placement needs to be carefully considered for best performance. Detectors may be diffusion types or pump (aspirated). The right choice is application dependant.
The range of measurement for the detector needs to be considered and that alarm levels meet HSE/COSHH/DSEAR requirements. In some cases, detectors may operate as stand-alone devices with their own in-built alarms and audible visual displays. Fixed detectors can also be either classified and approved for use in ATEX-zoned hazardous areas or what are termed safe areas. That choice will usually be based on a gas hazard survey and or a DSEAR report depending on the site and application. There is also a distinction between fixed detectors that are intended for life safety applications and those that are used for air quality monitoring. The latter will generally not be suitable or carry approvals for life safety application.
Fixed gas detectors are appropriate for use where the gas hazard is known, and detectors can be fitted strategically to detect leaks or emissions. In these situations, fixed systems meet BATNEEC requirements as a mitigation solution (Best Available Technology Not Entailing Excessive Cost). Consider also that areas not usually occupied can be more of a problem than areas that are normally occupied. There is always a duty of care to provide as safe an environment as possible for personnel.
Typical applications for fixed detectors would be:
- Plant rooms/Boiler rooms
- Laboratories (school, university, commercial)
- Test Facilities
- Process Areas
- Gas Storage and bottling
Pros:
- 24/7 continuous detection of the environment
- Can perform executive actions for example shut off gas supplies and provide site-wide alarms
- Remote alarms possible including GSM text and email alerts and cloud monitoring
- Clear unambiguous alarms if specified correctly
- Events can be recorded for HSE requirements
- Data can be logged for trending
Cons:
- Accurate detection is limited to gas that diffuses into the sensing inlet – requiring strategic placement of detectors
- Capital installation cost can be expensive depending on the amount of equipment required
- Demand constant power supply
- Requires regular service checks – just like a fire alarm system
Portable Gas Detectors
Portable gas detectors are designed to be carried or worn clipped to an item of clothing. They form part of a person’s PPE. This category of detector is a life safety device designed to provide alarms to the wearer when target gas levels exceed safety limits. They should not be mixed up with handheld gas leak detectors or analysers which are not intended as life safety devices. They can screen for hazardous species that may enter an operator’s breathing zone or be used for confined space entry testing. Portable gas detectors can be just for a single gas or may monitor for up to seven gas types. They may be diffusion-based or be pumped depending on the application. Portable gas detectors are intended for use where it is impractical to fit a fixed system.
Some application examples may be:
- Sewage workers
- Workers maintaining storage tanks (aircraft fuel tanks, process vessels, etc.)
- Gas delivery drivers
- Large process sites – generally in conjunction with a fixed system
Pros:
- Easily deployed
- Directly protects an individual
- Can be integrated with man down or lone worker alarms by GSM
- GSM linked units can be tracked centrally and monitored remotely
Cons:
- No automatic responses
- Operators must be trained
- Requires daily bump test
- Does not provide 24/7 monitoring
- Only protects a single user
- The user is wearing the unit and so is in the hazard when the detector alarms
- Has to be sent for calibration meaning cover units are required (multiple sets)
Deciding Between Fixed and Portable Gas Detectors
As a general rule: If it is at all practical a fixed system is always preferable to a portable gas detector.
Portable gas detectors may be required to verify alarms from the fixed system or on large sites to provide supplemental cover. If fixed systems are impractical (e.g. no one is fitting fixed gas detection systems in sewers) then use portables.
It is important to involve gas detection specialists at an early stage. You may identify through risk assessment a gas hazard. That is the safety requirement for any owner/operator. Once identified understanding the hazards of your application is critical to choosing between a fixed and/or a portable gas detector. A gas hazard overview will consider:
- How are gases stored?
- How are gases transmitted/delivered?
- How and where are gases used?
- By products of gas usage?
- Nature of the gas hazard and gas characteristics?
Solutions provided need to consider the best monitoring technology for the gas type and the environment in which it must operate. Suitable maintenance regimes and Safe Operating Procedures (SOP’s) must be established. People must know how to respond to alarms.
The above examples are deliberately reductive and are posed to offer a very basic idea of the differing applicability between fixed and portable gas detectors. There are, of course, myriad additional things to consider before selecting a gas sensing solution. Therefore, you should always consult the manufacturer or trained/certified distributor agent when it comes to selecting which equipment you require for your site.
For more examples about product selection, read our previous blog: Choosing the Right CO2 Portable Gas Detector
At International Gas Detectors, we supply a wide range of fixed and portable gas detection instruments for your convenience. Contact a member of the team today if you would like product specifications or to make a request for quotes.
