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Fixed or Portable Gas Detection?

Gas detection and monitoring systems are used as safety devices to alert workers of the potential danger of poisoning by toxic gas exposure, asphyxiation due to lack of oxygen or explosion caused by combustible gases. Choosing the right detector is critical - gas detectors save lives!

Gas detection instruments are generally available in two different formats: portable gas detectors and fixed gas detectors.

Several factors will depend on whether fixed or portable gas detectors are the most appropriate use for a particular application, including;

- Where gases come from
- How often the area is accessed by personnel
- Location and environmental conditions of the site
- Whether the hazard is permanent or temporary
- How often testing is needed
- Functionality of the product
- Cost of ownership

Portable Gas Detectors

Portable gas detectors also known as personal gas detectors and are designed to keep personnel safe from gas hazards by monitoring an operator’s breathing zone (25cm radius within the user's mouth) continuously, whilst stationary and moving about. Some personal gas detectors are also designed to test locations for safe entry such as confined spaces before they are entered. Personal gas detectors are generally handheld sized and are lightweight enough to be worn on clothing or a belt. These small devices are essential in many areas where gas hazards could occur.

With the tightening of health & safety rules, there is a big push to enhance safety and the integration of portable gas detectors helps with this. Changing legislation and regulatory compliance combined with evolving insurance pre-requisites are making the use of portable gas detectors more prevalent.

Advantages:

- Portable gas detectors cost less than fixed gas detection systems
- When personnel are under the threat of continuous exposure or face unpredictable conditions, personal monitoring with handheld or portable gas detectors is the safest measure
- Portable gas detectors can be taken anywhere with a user
- Most portable gas detectors are powered by batteries and not limited to a mains power source

Disadvantages:
- Users must be properly trained to ensure proper usage
- Portable gas detectors don't provide automatic responses

Fixed Gas Detectors

Through the use of relays and customisable alarm point settings, users are able to configure their fixed gas detection systems and gas transmitters to repsond to hazardous conditions. Relays may be activated to perform a number of fucntions including activating visual and audible alarms, closing electronic valves and opening/closing ventilation and exhaust fans. This type of automatic system alerts workers in hazardous situations and saves lives!

Advantages:

- Fixed detectors are generally put in places primarily to protect the facility, to detect catastrophic leaks or to be an early warning of gases leaking from a system
- In process operations, an area detector is used to sense a leak and alert the plant manager of the condition
- Process operations may also mean that ventilation or system shutdown occurs once gas levels reach an alarm level
- Fixed gas detectors are installed to monitor flammable and toxic gas levels to gauge danger and trigger alarms
- If the danger is contained to areas where personnel are restricted, then area monitoring with fixed gas detectors is an option

Disadvantages:

- Fixed gas detectors will only detect gas that diffuses into it which means that it’s completely cover the leak potential in any given area and the likelihood that a leaking gas and a worker both migrate to an area that is uncovered by a fixed detector is extremely high
- Fixed gas detection is more costly than portable detection
- The area may be small or hard to reach, making the placement of fixed gas detection impractical
- Gas detection systems tend to require mains power supply

 

Single-gas vs. multi-gas detector?

How many different gases are present in the workplace? If only one gas hazard exists, then a single-gas personal detector or single-gas fixed gas detector is appropriate.

Typical confined space atmospheres require pre-entry testing for combustible gases, oxygen deficiency or enrichment, and specific toxic gas measurements. Depending on the industry sector a mix of two or three toxic gas sensors is often required to cover the noxious dangers.

For personal protection, portable gas detectors in single or multi-gas configurations are available. Many companies have a mix of both based on the balance of their needs.

Fixed gas transmitters typically accommodate one or two sensors each, so multiple sensors are required to cover rooms or areas with multiple gas hazards.

 

How Many Gas Detectors Are Needed?

There are many ways to look at total usage for your gas detection needs; ultimately you need to look at the potential for risk of your workplace

- How many areas have the possibility of containing a gas hazard?
- How many employees will work continuously in those areas or pass through those possible areas of risk?

If you have personnel working in an area that has the potential for a gas leak (near gas bottle stores, gas piping or somewhere close to the source of emissions) or a confined space where gas may be encountered, then personnel should be equipped with a personal gas detector.

Unfortunately, there are no rules that cover all situations to make things easy. Some companies that purchase gas detection equipment may only use them during a 2-week maintenance shutdown procedure, while others use the equipment 24-hours every day of the year.

Fixed gas detectors are typically used to cover an area where the location and number of sensor heads depend on the type of gas being detected, the number of leak points and the size of the area.

 

Other Considerations

Confined Space Entry Testing

Confined space requirements include pre-testing of the environment prior to entry. This is achieved by drawing an air sample from various stages through the use of a remote sampling pump and tubing or a probe (not by lowering the gas detector on a piece of string!).

 

Datalogging

You may need to record the exposure data for industrial hygiene measurements, so data logging capabilities are critical.

Many companies measure Short Term Exposure Limits (STEL) and Time Weighted Average (TWA) readings as part of standard workplace industrial hygiene practices to evaluate employee exposure over the work period.

 

Alarms

For high noise areas, loud (greater than 100dB) or vibrating alarms are critical for alarm recognition. Check the manufacturers’ instrument alarm specifications as well as the availability of external alarms that provide audible and visual indications of danger.

 

Intrinsic Safety

For proof of intrinsically-safe equipment, look for third-party certifications or approvals, such as ATEX. All units intended for use in hazardous areas must comply with the ATEX directive when they are brought to the EU market. The directive details the minimum requirements for developing equipment for explosive dust and gas areas. Manufacturers have had the opportunity to have products certified for the past few years, so ask if the gas detector is ATEX certified.

 

Other Options

You will also have to assess whether power supply is available, consider whether you require a product that has a display or not, mounting options and an assortment of add-on accessories which make it easier to use a product or provide added protection such as rubber boots on personal gas detectors or water shields used to protect fixed sensors from splashes during cleaning.

Do not assume your site’s gas detection requirements are available from all manufacturers. Identify your workplace concerns and match the product to your needs.

 

Do You Need Some Help With Selecting the Right Gas Detection Equipment? 

If you have questions about any of our gas detection products or for help selecting the right equipment, simply contact us