Personal exposure monitoring in confined spaces

TSI Incorporated explains how its personal dust monitoring instruments can help mining companies and other industries protect workers from exposure to respirable particulates in underground mines and confined spaces.

Broadly speaking, a confined space is an area that is large enough for a worker to enter and do work, but is difficult to get in and out of easily and is not designed or intended for regular occupancy.

Examples of potential work spaces that fit that definition include storage tanks, silos, reaction vessels, enclosed drains, manholes, ship holds, sewers, mines, and utility or furnace rooms with facility operating systems.

While all of these examples can be considered a confined space that professionals often work in, not all confined spaces are the same.

Dangers of respirable dust and particulates in confined spaces

Particles 10 microns (PM10) in size and below become airborne easily and can be inhaled into a worker’s respiratory system.

Particles that are four microns (respirable) or smaller (PM4, PM2.5 and PM1) are able to enter the human respiratory tract and penetrate deep into the gas exchange region of the lungs.   

These small particles are typically generated from high energy work like cutting, grinding and sanding of materials or through high temperature process such as welding or in foundries.

Airborne dust and particulates are often made up of hazardous materials such as hexavalent chromium, lead, manganese, iron oxides, nickel, cadmium, silica, diesel particulate matter and other materials. 

Many of these materials are known to cause damage to organs in the human body such as the lungs, kidneys, liver, brain, nervous system and eyes. Many materials such as Silica are known to cause cancer. 

When generated in confined spaces, these dusts and particulates can build up quickly so it is important to monitor the particle concentration that a worker is being exposed to so that action can be taken to reduce the exposure and maintain worker safety. 

The best method for quickly determining exposure levels in real-time is with the use of direct reading instruments.

Real-time instruments can help workers quickly determine if the concentration of respirable particles is increasing in the work area and within the breathing zone of the worker. If so, workers can employ engineering controls to reduce exposure.

Even when engineering controls such as increased ventilation or dust evacuation methods are in place, it is important to monitor worker exposure in real-time to ensure the controls are effective or if further adjustments need to be made.

In recent years there has been a growing focus on personal monitoring of workers for silica dust and ultrafine particles, such as diesel particulate matter (DPM).

In 2016, the US OSHA reduced the personal exposure limit (PEL) of silica dust exposure levels to 50 µg/m3 averaged over an eight-hour period.

This is half of limit of the previous standard revision and OSHA added an action level of 25µg/m3 averaged over an eight-hour period. Many other countries have taken similar measures to minimise silica exposure to workers.

Silica exposure is potentially acute in confined spaces since the potential of limited air movement and minimal ambient air circulation in confined spaces, workers can generate significant silica and particulate concentrations which can build quickly.

Now, with the new lower PEL and action levels for respirable silica, defined exposure limits can be reached over a shorter period of time with high respirable particle concentrations in confined spaces.

Underground mining

Perhaps the best recognised confined space is underground mining. With the new silica standards being adapted, underground mining operations have increased concerns over respirable crystalline silica dust being generated by normal mining operations.

Compounding need for respirable dust monitoring is the increase in ‘Black Lung’ disease in coal miners around the world from long-term exposure to respirable coal dust by miners.

Ultrafine particles such as DPM is also a potential compounding factor for particulate monitoring in confined spaces. DPM is classified as a possible carcinogen by the National Institute for Occupational Safety and Health (NIOSH) and the US Environmental Protection Agency (USEPA).

The operation of diesel-powered equipment in underground mines and other confined or enclosed spaces can pose additional need for real-time personal exposure monitoring of particulates in the worker’s breathing zone.

Hazardous atmospheres and intrinsically safe personal aerosol monitors

Confined spaces in the underground mineral/metals mining, coal mining, petrochemical and oil and gas industries have the added complexity of workers performing duties in potentially volatile or explosive environments where gases, fuels or other potentially combustible materials are likely to be present.

As a result, many work areas in the mining, oil and gas, petrochemical and other industries require that electronic instruments like personal aerosol monitoring instruments be certified for intrinsically safe design so they will not have the potential to cause the ignition of specific gases or other combustible materials within the work area.

In work areas that are designated as explosive or potentially volatile, only intrinsically safe instruments that have been certified by IECEx / ATEX or CSA are allowed into the work area.

Certifications for real-time personal exposure monitors require specific design requirements with rigorous testing and verification. 

Few real-time particle monitoring instruments, such as the SidePak AM520i Personal Aerosol Monitor from TSI, can meet the ‘EX’ certification standards for applications requiring intrinsically safe instruments such as confined spaces.

Also, beyond the IS certifications above, the confined nature and hazard of underground mines typically require additional certifications.  Almost every country requires instruments used in underground mines to be certified as intrinsically safe for mining in that country which requires manufacturers to go through additional reviews, investigations and testing.

Australia, for example, requires an additional IECEx-SIM certification from local authorities for Australian mining.


Monitoring workers for exposure to respirable particulates that include dust, metals, crystalline silica, welding fumes, diesel particulate matter and other potentially harmful particles is being driven by tighter regulations affecting almost every industry.

Employers are more attentive than ever regarding the personal exposure of workers and the workers themselves are being educated to the potential dangers and health risks of respirable, fine and ultrafine particles in the workplace and how to avoid exposure. 

Instrument companies like TSI are developing new personal exposure monitoring instruments that are certified for intrinsically safe design to help companies obtain the critical personal exposure data needed to help keep workers safe even in confined spaces.

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