This page aims to answer all your important questions about gas measurement and sensor technologies as well as the maintenance and operation of our devices. You will also find definitions of relevant gas detection terms in our glossary.

General information and questions about GfG products

We offer our customers portable gas detection devices and fixed gas detection systems in numerous versions. The best way to find out which device variant is most suitable for your application is an individual and personal consultation.

We strongly recommend carrying out a daily visual inspection (for mechanical damage and contamination) and a bump test to increase occupational safety when handling our portable gas detectors. You will also have to perform function checks and sensor adjustments on a regular basis. Please adhere to the applicable national regulations and requirements of your industry as well as the operating manual. For maintenance and repair work, please contact GfG or your sales partner.

The devices have different sensor equipment and ATEX approvals:

  • G999C: 1 catalytic combustion sensor, 3 electrochemical sensors, 1 infrared sensor (Ex zone 1).
  • G999M: same sensor equipment as G999C, but suitable for use in Ex zone 0
  • G999E: 4 electrochemical sensors, 1 infrared sensor (Ex zone 0)
  • G999P: 1 photoionization detector, 3 electrochemical sensors, 1 infrared sensor (Ex zone 0)

These configurations "C" and "M" also apply to the G888 series.

This question cannot be answered simply by stating an area in square metres. It depends on a variety of factors: The type of gas, possible leakage points and the type of ventilation influence the number and the correct installation location of the transmitters. It is essential to take advantage of GfG's advice in advance.

That depends heavily on the device and sensors you are intending to use and the gases you need to measure. GfG's portable gas detectors have slots for a maximum of five different sensors, giving them the ability to measure up to eight gases simultaneously, depending on their sensor configuration. The transmitters used in fixed gas detection systems usually have only one sensor and can therefore only measure a single gas. We will be happy to assist you in finding the best solution for your individual needs in a consultation meeting.

No clear answer can be given to this question as a general rule, as the service life depends on the usage times of the device and the charging cycles. However, the service life of a rechargeable battery is limited. At some point, the ability to store energy is only partially available. This can be seen in the longer charging times and shortened usage times. In this case, a new battery must be inserted by GfG Service.

The sensors, like the batteries, only have a limited service life. The approximation we can give is only a guideline and will be affected by factors like ambient conditions (mainly temperature and humidity) and their exposure to gases. Sensors will therefore sometimes have to be replaced before the expected end of their service life. The measuring principle also influences their service life. Infrared sensors, for example, will usually last longer than electrochemical sensors. For more detailed information, please refer to your product's user manual. 

This is usually due to the cross-sensitivity of the sensor. This means that a sensor does not respond exclusively to the target gas, but also to other influencing variables. In other words, a sensor with cross-sensitivity does not have perfect selectivity. This is particularly challenging for gas sensors, because the measurement of a specific gas should ideally be possible in a gas matrix of any complexity - with hundreds of gases and vapors potentially interfering. However, perhaps unsurprisingly, almost all measuring principles used in gas sensors exhibit some degree of cross-sensitivity to at least one other gas. 
In addition to cross-sensitivity, however, humidity or temperature can also falsify the displayed result.

Equipment used in hazardous locations that are subject to the potential presence of explosive gas must be designed and certified as safe for use in the intended area for the intended purpose.  Different countries or groups of countries (like the European Union) have different certification requirements.  GfG instruments are sold all over the world, so they need to carry a lot of different national and harmonized international certifications! 

Combustible gas hazardous locations are areas where the atmosphere contains, or has the reasonable potential for containing, flammable gases and vapors.  A flammable concentration of gas is one that is capable of being ignited if a source of ignition is present. When you are working in an area with the potential presence of an explosive gas, you can’t afford to take a chance with the equipment! 

In countries that belong to the European Union, GfG instruments are sold under their ATEX Certifications. EEC directives require that equipment and protective systems intended for use in potentially explosive atmospheres must carry ATEX (Atmosphères Explosibles) certification. If a product / piece of equipment has official ATEX certification, it has been fully tested and approved to be safe to use in hazardous / explosive atmospheres.  GfG instruments also carry CE (Conformitè Europëenne) certification which indicates that the product conforms with all other relevant EEC product norms and directives.  

GfG instruments also carry International Electrotechnical Commission (IEC) Certifications to standards relating to equipment for use in explosive atmospheres (IECEx System).  IECEx certifications are based on harmonized international standards that are recognized by the signatory nations that belong to the IEC.

Combustible gas hazardous locations are defined a little differently in North America compared to the UK and Europe.  In North America, the most widely used hazardous location classification scheme is based on the National Electric Code (NEC) NFPA® 70, Articles 500 - 506.  The NFPA® scheme divides hazardous locations into three classes that are based on the characteristics of the flammable materials.  “Class I” includes gases and vapors. The classes are further divided into divisions based on the risk of fire or explosion the class of material represents, and the probability of being present in in a potentially hazardous quantity. 

The NEC / NFPA® scheme divides flammable gases into four “gas groups” identified by means of a “typical” gas with flammability characteristics that fall into the group. The groups include additional gases with similar flammability characteristics. For instance, the most highly explosive gas is acetylene, which is in Group A. Group B includes hydrogen, butadiene, and other gases with similar flammability characteristics. Group C includes ethylene, while Group D includes ammonia, ethanol, methanol, natural gas, methane, acetone, and many other VOC vapors, as well as propane.

In the UK and Europe, the hazardous location classification scheme is based on “Zones” that are defined by International Electrotechnical Commission (IEC) and European Committee for Electrotechnical Standardization (CENELEC) standards. 

Portable GfG instruments sold in North and South America carry multiple CSA® certifications as intrinsically safe for use in hazardous locations. Most GfG portable instruments are c-CSA-us Certified® as Intrinsically Safe for use in Hazardous Locations characterized by the presence of Class I Division 1 Gas Groups A, B, C and D combustible gases.  The small “usa” in the certification marking indicates the instrument has been tested and verified to be in conformity with all relevant USA requirements.  The coveted small “c” in the marking indicates conformity with the even more rigorous requirements for sale in Canada. 

Most GfG portables carry a second CSA® certification according to the IECEx Zone scheme.  These instruments are c-CSA-us Certified® as intrinsically safe for use in Zone 0 hazardous locations. The difference between Zone 0 and Zone 1 certification sounds minor, but it is a really big deal. In Zone 1 hazardous locations ignitable concentrations of gas can occur but are not common.  In Zone 0 locations ignitable concentrations of gas are always expected to be potentially present.

The Zone classification scheme is more and more commonly being used in the USA and Canada. Many refineries, chemical plants, gas production and transmission facilities and oil platforms have designated Zone 0 areas. Any equipment taken beyond the HAZLOC perimeter must have Zone 0 certification. This is not a problem for GfG!

GfG instruments are also available in special versions that carry additional certifications. For instance, the G450 4 gas monitor is available in an MSHA (Mine Safety and Health Administration) Certified version. An MSHA certification is required for instruments that are used at MSHA regulated sites.  Some state agencies also require MSHA certification for instruments used in certain applications, such as underground tunneling and construction. 

Finally, GfG instruments carry many additional certifications for use in specific countries or activities. Some of these additional certifications include Inmetro Certification for sale in Brazil, SABS Certification (South African Bureau of Standards) for sale in South Africa.

As part of the certification requirements, GfG Quality Systems and production procedures are audited multiple times per year by the NRTL or “Notified Body” that issues the certification. Maintaining, updating, and adding new certifications is a full-time job for several of our engineers in the USA and Europe. And as you might expect, securing and maintaining these certifications is an extremely expensive process.  But it is absolutely worth every penny when it comes to ensuring GfG instruments are safe for our customers use in hazardous locations! 

If you are interested in this topic, GfG has an excellent application note, “Protective Concepts in Combustible Gas and Vapor Detection” , that discusses certification and electrical safety issues in greater detail. This app note, AP1024, can be found on the Support tab then Downloads and Application Notes.

Atmospheric monitors use sensors to measure gas. Some types of sensors need more power, while other types need less power. Very low power sensors may use so little power that a set of disposable or rechargeable batteries can last for months or years of operation. But no matter what kind of sensors are installed, portable atmospheric monitors need power, and that means the instrument depends on batteries. 

There is no perfect type of battery. Each type of battery has benefits and liabilities. Very importantly, how well the instrument performs is a combination of the type and capacity of the batteries, the type of sensors installed, the environmental conditions in which the instrument is used, and the power requirements of the instrument electronics.

There are three major types of batteries that are commonly used in portable instruments: disposable alkaline, rechargeable lithium ion (Li-ion) and rechargeable nickel metal hydride (NiMH) batteries.

Portable instruments can be powered by disposable alkaline batteries, rechargeable batteries, or may be able to use both types of batteries. A primary advantage of rechargeable batteries is overall cost effectiveness. Frequent (or daily) replacement of disposable batteries can be expensive; and is increasingly viewed as environmentally objectionable. Some instrument designs offer interchangeable rechargeable and alkaline battery packs. Other designs allow the optional use of either alkaline or “off the shelf” rechargeable batteries.

Contractors who only use their instruments occasionally often find disposable batteries are an easier solution than charging and maintaining rechargeable batteries. For other instrument users, simply having the ability to use disposable batteries “in a pinch” is a strong design advantage.   

Make sure any disposable or rechargeable off-the-shelf batteries you use are approved by the manufacturer. The owner’s manual will list the batteries which are approved for use. Using a non-approved battery, even if it fits the instrument and seems to work, can void intrinsic safety and other certifications carried by the instrument.   

Alkaline batteries have the benefit of convenience, but they suffer from poor performance in low temperatures. Generally, when the temperature is below freezing, instrument users should avoid alkaline batteries. The batteries may work for a while, but once the internal temperature in the battery drops below freezing, the amount of available power drops as well.

The most common types of rechargeable batteries are lithium ion (Li-ion) and nickel metal hydride (NiMH) batteries. Each type of rechargeable battery has specific advantages and limitations. The weight of the instrument, run time, time to recharge the battery and the number of charging cycles that the battery can survive without loss of capacity are all affected by the type of battery included in the design. Less obviously, the temperature code and operating ambient temperature range over which the instrument’s certification for intrinsic safety applies are also affected (or limited) by the type of batteries used in the design.

Battery and battery charger manufacturers have made major improvements in their designs over the last few years. Today's "smart" battery chargers contain electronics for assessing the condition of the battery pack during charging and are able to drop from a "fast" charge rate to a "trickle" the moment charging is complete. The "trickle" charging rate is too low to produce damage or loss of capacity due to heating. As a result, instruments containing rechargeable batteries can be recharged in a very short period, while still being left on the charger for long periods of time without damage.

Li-ion batteries do not suffer from charging “memory” issues, and they do not lose capacity as a function of over-charging or lack of exercise. Li-ion batteries do not require periodic cycling to prolong life. Li-ion batteries have low internal self-discharge rates and lose power only very slowly in storage. The materials used in Li-ion batteries are environmentally friendly, and Li-ion batteries are better in cold temperatures than alkaline batteries.

Lithium ion batteries share a major concern. The electrolyte is a flammable liquid, and Li-ion batteries are prone to internal short-circuiting if mechanically damaged.

If you slice a Li-Ion battery in half it looks like a jelly roll with many extremely thin layers. A non-conductive separator layer is used to keep the cathode and anode layers apart. The electrolyte consists of salts and other additives in a solvent solution. It serves as the conduit of lithium ions between the cathode and anode layers. Mechanical damage that allows the anode and cathode material to directly come into contact can lead to run-away short circuiting, which causes the battery to heat. When the internal temperature reaches the auto-ignition temperature of the electrolyte, the battery can burst into flame.

Li-ion battery fires are extremely difficult to put out!  This is the reason that airlines prohibit electronic devices equipped with rechargeable Li-ion batteries being checked in baggage. While you are allowed to take Li-ion battery equipped devices with you into the cabin, the safety briefing warns you to be careful you do not do anything that could mechanically damage the device, (like getting it caught in a reclining seat mechanism). If you have ever seen video footage of a burning Li-ion battery pack, you will know why the airlines are so concerned. 

Nickel metal hydride (NiMH) batteries have several safety advantages over Li-ion batteries. The electrolyte is not flammable, and they are not prone to run-away short circuiting. NiMH batteries are generally the best choice for low temperature operation. While all types of rechargeable batteries are affected by cold temperatures, NiMH batteries are typically usable down to -20°F (-29°C) with only a modest loss of operation time. They can be used for shorter periods of time in even colder temperatures.

NiMH batteries are durable and able to survive up to 500 complete charging cycles without a significant loss of capacity. To avoid harming the battery, compared to Li-Ion battery chargers, NiMH chargers can take a little longer to fully recharge depleted batteries. While rechargeable NiMH batteries can be left on the charger for prolonged periods of time without damage, they still benefit from periodically being deep-discharged, and most instruments that include this type of battery also include an automatic deep discharge cycle.

For maximum flexibility, being able to use disposable batteries is a strong design advantage. But when battery safety, cold temperature operation, and / or the certifications carried by the instrument are the major concerns, NiMH batteries are usually the best choice.

According to 29 CFR 1910.146, a confined space is characterized by the simultaneous existence of three conditions:

  1. It must be large enough and so configured that it is possible for a person to bodily enter and perform work.
  2. It has limited or restricted means for entry and exit.
  3. It is not designed for continuous employee occupancy.

Confined spaces include everything from railroad tank cars, to sewers, boilers, open topped pits, aircraft wing tanks, fuel storage tanks, vaults, manholes, elevator pits, and many other common workplace environments. 

Just because a space meets the basic confined space definition, however, doesn’t automatically trigger any special workplace procedures beyond those for similar activities undertaken in any other non-confined space environments.  Non-permit confined spaces are by definition not associated with any additional serious safety hazards. 

Many confined spaces are associated with serious safety hazards, and require special procedures to ensure worker safety. 

According to 29 CFR 1910.146, a permit-required confined space (or permit space) is a confined space that contains hazards capable of causing death or serious physical harm.  Besides the basic three conditions common to all confined spaces, a permit-required confined space contains at least one additional serious or recognized danger such as:

  1. The potential to contain or generate a hazardous atmosphere, (such as oxygen deficiency from rusting metal, combustible methane from decomposing leaves or debris, or hydrogen sulfide from sewage).
  2. The space contains a material that has the potential for engulfing an entrant, (anything from water, to mud, to wood chips, to molasses).
  3. An internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section, (such as many bins, chutes and dust collectors).
  4. Or any other recognized serious safety or health hazard, (from rotating blades or vanes, to poisonous snakes).

It is important to always remain on the lookout for conditions or activities that may change the dangers associated with a confined space.  Activities such as hot-work, using degreasers or painting may introduce additional potential hazards that change the classification of the space from a non-permit, to a permit-required confined space (PRCS).

Permit space entry team members can only function effectively and safely when they fully understand their responsibilities and duties.  Thorough training is essential.  Permit spaces are by definition inherently dangerous.  Mistakes are “Not Permitted!”

Once the environment has been identified as a permit space that contains at least one additional serious safety hazard, the next question is what to do about it.  There is more than one option. 

     1. Permanently eliminate the need for entry

In some cases, the employer may elect to permanently secure the space to prevent entries.  Since the space is no longer subject to entry, there is no need to develop procedures governing entry into the space.  Another common approach is to relocate valves and controls outside, rather than inside of confined spaces.

     2. Implement engineering controls that permanently eliminate or control the dangerous condition(s)

A confined space is not designed for continuous worker occupancy.  If the hazardous conditions in the space are permanently eliminated or controlled, and the space has been rendered safe for continuous occupancy, it no longer meets the basic definition of a confined space.  It is simply a non-hazardous enclosed space where work is performed.  

For instance, a continuous gas detection and ventilation system might be used to ensure that an enclosed space is safe for continuous occupancy by workers.  The system is designed such that a fault in the ventilation system, or the presence of gas, triggers an alarm that allows workers to safely leave the area before conditions become hazardous.

When entry into the permit space can’t be avoided, employers have three options.

  1. Reclassification
  2. Alternate entry procedures
  3. Permit program

1.  Reclassification

In some cases it may be possible to completely eliminate all hazards from the space without having to enter the space in order to do so.  In this case it may be possible to temporarily reclassify the PRCS as a non-permit space.  Non-permit spaces are confined spaces, but do not require a permit for entry, because the hazards have been eliminated.  The reclassification continues only as long as all hazards remain eliminated. 

2.  Alternate Entry Procedures

In cases where the only hazards are exclusively atmospheric in nature, and where continuous forced air ventilation alone is sufficient to maintain the permit space safe for entry, entry may be by means of the “Alternate Entry Procedures” contained in Paragraph (c) (5) (ii) of the standard. 

The alternate entry procedures require that before employees enter, the internal atmosphere must be tested for:

  1. Oxygen content,
  2. Flammable gases and vapors, and
  3. Potential toxic air contaminants

Once testing has been completed, the atmosphere within the space must be periodically tested, or continuously monitored, to ensure that the atmosphere remains safe for the entrants.  There must be no hazardous atmosphere within the space when an employee is inside the space. If a hazardous atmosphere is detected during entry, employees must exit immediately, the space must be evaluated, and corrective measures must be taken.

When entries are undertaken by means of the Alternate Entry Procedures, there are no formal requirements for the presence of an attendant, entry supervisor, or standby rescue team.  Solo entries are permitted.  The emphasis is squarely on use of continuous ventilation, and atmospheric monitoring to ensure that atmospheric hazards are controlled, and that the atmosphere remains safe for entry. 

Because of the reliance on atmospheric monitoring to verify that conditions remain safe, the “best practice” followed by many employers is to define “hazardous atmosphere” more conservatively than in other types of confined space entry.  As an example, a concentration of 5% LEL rather than 10% LEL combustible gas, or a concentration of one half the normal permissible exposure limit (PEL) concentration of a toxic gas might be used as the employer’s hazardous condition threshold used during “Alternate” entry procedures.

3.  Permit Entry procedures

If the hazard cannot be eliminated or controlled, then the only remaining option for entry is the implementation of a comprehensive permit space program. 

Paragraph (c) (4) of the standard requires employers whose employees enter permit spaces to establish a written permit space program (permit program).  Employers must make this written program available to employees and their authorized representatives.  The written program includes specific details regarding how the employer will comply with each of the requirements of 1910.146.  Employer obligations include: 

  1. To secure permit spaces to prevent unauthorized entry.
  2. To evaluate and identify hazards before entry.
  3. To implement operation procedures that ensures safe entry.
  4. To provide and maintain the necessary equipment.
  5. To evaluate PRCS conditions.
  6. To provide attendant(s).
  7. To develop and implement the specific methods to be used if attendants are responsible for monitoring more than one PRCS at the same time, or if an emergency occurs.
  8. To designate the roles and responsibilities of all active PRCS entry team personnel.
  9. To develop and implement effective rescue and emergency procedures.
  10. To develop and implement an entry permit system.
  11. To develop and implement procedures to coordinate entry operations when employees of more than one employer will enter a PRCS.
  12. To develop and implement procedures for concluding an entry.
  13. To periodically review entry operations.
  14. To periodically review the permit space system.


Adjustments of the zero point and the sensitivity of the gas detector / sensor with a known zero gas or test gas.

Setting of the device to a specific gas concentration at which a display, alarm or other output signal is triggered by the device. The alarms and the measures to be taken when an alarm is triggered must be determined specifically for each application as part of its risk assessment.

All GfG devices with catalytic sensors for combustible gases and vapors (CC) have an integrated protective function. If the measuring range is exceeded by 12 percent (112 % LEL), the sensor is disabled for safety reasons. One reason for that is the risk of explosion. The other is that the measuring signal would decrease again with increasing gas concentration, as there would be no oxygen available at the sensor, which is required for catalytic combustion.
The ambiguity would occur at the point where, while the gas signal was falling, one could no longer differentiate between a decrease in the actual gas concentration or an increase in the gas concentration in the absence of oxygen.
Disabling the CC sensor also prevents excessive wear at such high concentrations of combustible gases. Only when it has been ensured that no more combustible gas is present at the device may this condition be eliminated with an acknowledgement by the user. During this time, the device will clearly indicate the measurement range being exceeded. 

Comparison of the values displayed on a gas detector / sensor with a known test gas concentration without adjusting. Depending on the degree of deviation detected

  • the device can continue to operate within the permissible deviation from the setpoint
  • the device must be adjusted
  • the device must be repaired

A gas that causes the sensor to react even if the sample gas is not present or falsifies the measurement result when sample gas is present.

In general, the cross-sensitivity of a measuring device describes its sensitivity to variables other than the measured one. In gas detection, the cross-sensitivity describes how strongly and to which other gases a sensor reacts. The lower the cross-sensitivity, the more accurate the expected measurement results for the monitored gas will be. 

These abbreviations denote explosive (EX), toxic (TOX) gases and oxygen (OX).

Explosion-proof in this case means that devices may be used and operated in potentially explosive atmospheres. Many GfG devices have this so-called ATEX certification. They have the required safety and cannot trigger the ignition of hazardous air-gas mixtures in potentially explosive atmospheres.

The International Protection class (IP; also Ingress Protection) indicates how securely the equipment is protected against the ingress of solid foreign bodies and water. IP is indicated followed by 2 digits. The first digit (0-6) stands for the degree of protection against solid bodies and the second digit (0-9) for the degree of protection against the ingress of water. The higher the digits, the higher the protection.

Within the field of explosion protection, there is the type of protection. This represents various design principles of equipment and is intended to minimize the risk of the simultaneous presence of an explosive atmosphere and ignition sources. Intrinsic safety "i" is the technical property of a device that ensures that no unsafe condition occurs even in the event of a fault. The current strength and voltage are limited to values that do not permit ignition of explosive air-gas mixtures either by sparks or by heating.

Flammable gases and vapours in air only form explosive mixtures within a certain concentration range. Below and above these lower and upper explosion limits, the gas-air mixtures are not explosive. Up to the lower explosion limit (LEL), the gas-air mixture is too lean for combustion. Above the upper explosion limit (UEL), the oxygen required for combustion is not present in sufficient quantities.

  • threshold limit value - time-weighted average (TLV-TWA): average exposure on the basis of a 8h/day, 40h/week work schedule
  • threshold limit value − short-term exposure limit (TLV-STEL): a 15-minute TWA exposure that should not be exceeded at any time during a workday, even if the 8-hour TWA is within the TLV-TWA.
  • threshold limit value − ceiling limit (TLV-C): absolute exposure limit that should not be exceeded at any time

Gas/air mixture used as a substitute for any test gases that would be too difficult to handle on a regular basis.

The t100 setting time is the time span that a measuring device needs to react to an abrupt change in the value of the measurand with a corresponding change in the measuring signal. The change in the measurement signal itself is not erratic, but runs in the form of a logarithmic curve, i.e. one that becomes increasingly flat with time. The shorter the adjustment time, the faster a transmitter, for example, displays the actual concentration of a gas.

Since it takes a disproportionately long time to settle to the last 10% accuracy both when rising and when falling, intermediate values such as t90, t50 or, in the case of falling gas concentration, t₁₀ are much more important in practice. With sufficient accuracy, they deliver significantly better.

The gas or gas mixture to be monitored. It usually consists of air, the target gas and other components.

The gas or gaseous substance you want to detect.

Gas mixture of known composition used for the calibration and adjustment of gas detection devices.

Describes the time from switching on the gas detection device until it reaches readiness.

Test gas that contains neither the target gas nor interfering impurities.

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