Indoor air contaminants come in a variety of forms and originate from multiple sources. Interactions between building materials and furnishings, activities and equipment inside the building, internal temperature and relative humidity, filtration and ventilation system operations, climate and building occupants all contribute to the indoor air quality (IAQ) in commercial, industrial, residential and medical buildings. Poor IAQ can cause a number of health issues such as, allergies, dryness and irritation to the eyes, nose, throat, and skin. It can also cause headaches, shortness of breath, hypersensitivity, sinus congestion, coughing, sneezing, nausea, and dizziness. Sick employees are less productive, more likely to be absent from work and can amount to a considerable cost to the employer.

Depending on the type of building, the main causes of poor indoor air quality are different. For residential homes, carbon monoxide, pet dander, dust mites and mold spores are some common contributors. In recreational centers with arenas and swimming pools, there is the possibility of ammonia, carbon monoxide, chlorine and ozone leaks and/or carbon dioxide build-up. For public places like shopping malls, grocery stores, airports, hospitals and parking garages the main concerns are carbon monoxide and nitrogen dioxide gases from gas and diesel engine exhaust in vehicle parking areas or potentially being drawn indoors from improperly operating ventilation equipment or delivery vehicles left running while parked close to large building air intakes.

Commercial processing and manufacturing plants have a multitude of possible indoor air contaminants that can affect employees’ health and safety. Depending on what is being made with what type of products and equipment, gases such as ammonia, carbon dioxide, carbon monoxide, combustible gases, nitrogen dioxide and many other are possible threats to the quality of air in the workplace.

Office environments may contain carbon dioxide, formaldehyde, toxic vapours from cleansers, dust mites, microbial contaminants and ozone from photocopiers, electrostatic air cleaners and air conditioning systems. Combine an office environment with a manufacturing or warehousing plant adds the need to monitor both environments to ensure healthy air quality.

We spend tens of thousands of hours at work in our lifetime. We expect our working environment to be safeguarded against potential dangers and hazards and employers are responsible for meeting that expectation. Indoor air quality testing, diagnostics and monitoring of hazardous gases can be accomplished by fixed gas detection systems and/or portable gas monitors. Both products are equally capable of doing the job they are meant to do, in the type of areas they are meant to do it in.

When deciding which system to use you must take into consideration the physical area to be monitored, the type of gas(es) to be monitored, whether the hazard is permanent or transitory, the level of risk to workers and the practicality and cost effectiveness of using either or both systems. Monitoring for single or multiple hazardous gases in large areas populated with many people is best achieved by having a fixed gas detection system. Portable IAQ monitors are perfect for detecting gases in confined spaces or smaller areas where people occasionally go. Particulate monitors with temperature and relative humidity readings are ideal for dusty or smoky areas.

Fixed Gas Detection Systems

Portable Gas Monitors

Permanently installed, stationary systems that are practically invisible to the general worker population until the alarm sounds and evacuation procedures need to be followed.

Assigned to workers who keep them on their person as they move around. Each worker requires their own unit and training on how to use it.

Ideal for large areas populated by many workers and/or areas where worker movement is unrestricted. Somewhat impractical for detection in confined spaces such as sewers, storage tanks, pits, fermenters, etc.

Ideal for small areas such as confined spaces and/or areas where security clearance to enter is required. Very costly if used as the only gas detection system for large areas such as a manufacturing plant with lots of equipment and workers.

Monitoring is continuous and the power source is (generally) constantly available and devices don’t need to warm up prior to each use.

Monitoring is only when the unit is on, warmed up and the battery is charged.

Does not need to warm up prior to each use.

Warm up period required each time the device is turned on.

Bump testing suggested every 30 days.

Bump testing recommended before each use.

Wide range of sensor type combinations available.

Combinations of sensor types are limited.

Ideal for monitoring any type of toxic, combustible or refrigerant gas because devices are strategically placed in key locations where the hazardous gas is likely to accumulate.

Where the worker goes, the monitor goes and heavier gases that concentrate inches off the floor or lighter gases that rise overhead may not be detected until concentration levels are serious.

Sensors can have longer life expectancies because in some cases they are larger.

Compact, handheld devices tend to accommodate small sensors, which don’t have the same lifespan as larger sensors.

Devices are fixed in one place reducing the rate of wear and tear and they can be shielded from damage with a splash guard and/or metal protective guard.

Devices more likely to sustain wear and tear and/or damage due to human negligence and the fact it is physically moved around in different environments.

Typically have analog and/or digital output(s) so remote alarms can be turned on and/or safety processes can be triggered (ie. fans turn on, systems shut off, etc.)

When hazardous gas is present above an acceptable limit, an audible alarm sounds, LEDs flash and a vibrating alarm is activated if the unit is so equipped.

Working together:

The portable gas monitor is advantageous for locating the exact point of a leak that has first been detected by the fixed system when using an attached probe.

The portable gas monitor is convenient for detecting a single gas that may be likely to leak in a small area where workers occasionally go, while the fixed system concurrently and constantly monitors the general areas for other hazardous gases.


In addition to monitoring the air quality, it is important that the design, maintenance and operation of the building’s ventilation, heating and air conditioning systems be working properly. HVAC systems can sometimes act as a source of pollutants and they can also have a significant impact on how pollutants are distributed and removed.

For suggestions on gas detection systems, indoor air quality monitors and calibration, please visit

Austin, Alan K. (2005, January). Portable Versus Fixed Gas Detectors: Which One Do You Need? Industrial Hygiene News. Retrieved from
Boettern, Lars (2000,  January 1). When to Use Fixed Rather Than Portable Gas Detectors. Retrieved from