Health and Safety issues
While comfort is important in maintaining productivity and concentration, many unwanted airborne contaminants can actually pose a threat to human health. Unhealthy IAQ conditions occur whenever vapours, gases or airborne particulates are present in concentrations that adversely affect one or more occupants of a space. Potentially toxic, infectious, allergenic, irritating or otherwise harmful substances are almost always around us. Usually they exist in such small concentrations that stay below a “trigger” threshold and get little attention. When concentrations rise above the threshold, problems can arise. Even at relatively low concentrations, some individuals are very sensitive to certain substances and may react adversely even though other area occupants are not bothered. In very extreme cases, concentrations may be high enough to be fatal to all occupants. Dangerous airborne substances are serious matters and must be dealt with, proactively, before problems get out of control.
Carbon Monoxide
The US EPA has set National Primary Ambient Air Quality Standards for Outdoor Air to be used in locating ventilation sources for buildings. Exposure limits for CO are an average of 35 ppm for one hour, not more than one time per year, or 9 ppm over any eight-hour period. The American Conference of Government Industrial Hygienists (ACGIH) and US Occupational Safety and Health Administration (OSHA) have also set maximum exposure limits in the Industrial Workplace Standard.
Measurements of carbon monoxide should be taken periodically and spread throughout many areas in a building to be sure that air is being distributed evenly and no dangerous levels of CO are detected. Pay particular attention to areas in which any form of combustion takes place. Typical examples of outdoor CO sources in a building include vehicular emissions from traffic or parking areas and building exhaust stacks. Indoor sources include furnaces, boilers, stoves and smoking areas. Instruments that measure carbon monoxide in real time include the IAQ monitors and combustion analyzers.
Airborne Particles
Respiration of particles challenges the body’s natural defence mechanisms and overexposure may strain these mechanisms, causing an adverse reaction. Inhalable particles are typically defined as those with an aerodynamic diameter of 10 micrometers or smaller, commonly referred to as PM10. Respirable particles, or those that readily enter the lungs, are usually classified as less than 4 microns in diameter. Sources may include dust, mists, fumes, smoke, environmental tobacco smoke (ETS) and other particulate by-products of combustion. ASHRAE Standard 62 recommends a maximum exposure limit for PM10 particles of 0.15 mg/m3 for a 24-hour average and 0.05 mg/m3 for an annual average exposure. This is consistent with the EPA’s National Ambient Air Quality Standards. The industry is moving in the direction of concern for smaller particles since they bypass natural defence mechanisms more readily and make their way deep into the lungs.
Three types of instruments – photometers, optical particle counters and condensation particle counters – normally are used for real-time measurements. Performance features and applications for the three are compared in the following charts. The specific instrument of choice depends on the application and the desired results.
Ultrafine Particles
Ultrafine particles (UFPs), defined as particles less than 0.1 micrometer diameter, are often produced by combustion and some chemical reactions. They are so small that they can pass easily through the body’s natural defence mechanisms to the deepest areas of the lungs. Certain people are extremely sensitive to ultrafine particles, sometimes regardless of chemical composition. It is suspected that the sheer number of particles and their cumulative surface area may trigger a reaction in these people. The only practical instrument for detecting ultrafine particles is a condensation particle counter (CPC), a device that “grows” the small particles to a size large enough to be counted using conventional particle counting techniques. The counter employs CPC technology to detect and track ultrafine particles within the building environment.
The method for tracking UFPs begins outdoors where several measurements are made with the particle counter to establish a baseline. If the building’s intake air is filtered, you can subtract from the base-line measurement percentage of particulates roughly equal to the efficiency rating of the filter to establish an indoor goal. For example, a 75% efficient filter effectively removes about three-quarters of all particles leaving 25% of the outdoor reading as the goal. Inside, measurements are taken and compared to this indoor goal. Seek levels of ultrafine particles greater than the goal to find sources of particles that might contribute to air quality problems. A basic understanding of the ventilation system and how outdoor air is introduced, filtered and distributed throughout the building is necessary for an effective investigation.
If levels of ultrafine particles significantly higher than expected are found anywhere in the building, take steps to locate and identify the source. Using the particle counter much like a Geiger counter, ultrafines can be traced quickly and easily directly to their source. Once a source is located, remedial action to control, repair or remove it is often straightforward. Another important parameter to consider along with ultrafine particles is differential air pressure. Airborne particles travel along seen and unseen pathways and are driven by air movement and pressure differential. Small particles naturally migrate from areas of higher to lower relative pressure.
Bioaer
osols
Some of these bioaerosols contain dangerous toxins that in extreme cases can cause a range of adverse health effects, including death. Besides serious diseases, some bioaerosols can also cause varying levels of irritation in certain individuals, including allergic reactions, headaches, eye irritation, sneezing, fatigue, nausea, difficult breathing and more.
Most biological growth requires some kind of food and water. Condensation, plumbing leaks, roof leaks, or even improper housekeeping can lead to unwanted moisture which can foster unwanted growth that must be checked and corrected. At this time, bioaerosols such as molds, fungi and bacteria must be collected, cultured and analyzed in an environmental microbiology laboratory setting to determine exactly what they are and how large of a presence they have. Sampling often consists of collecting material through an air sample on different sized filter media. In commercial and residential environments, “settle plates” and surface swabbing are not viable means of testing for biologicals. These methods were developed for testing in highly controlled environments and may grossly understate or overstate the condition in commercial and residential environments.
Some of the tools available to measure include electrochemical and infrared (NDIR) gas sensors designed to identify particular gases present in industrial settings, from combustions, emissions and other situations that could impact air quality. Photo-ionization and flame-ionization detectors can be used to identify many VOCs that can impact IAQ. In most cases, it is difficult to get an accurate picture of the extent of chemical contaminants in the air using real-time data collection. It is more often a complex mix rather than individual compounds that pose the difficult challenge. Consequently, sampling is an accepted practice generally conducted using techniques such as filtration, absorption in another media, or impaction.
It is important here to recognize that a healthy, productive working or living environment consists of more than just good quality air. The entire picture must be considered in order to optimize occupant satisfaction and productivity.
Indoor Air Quality Handbook, ASHREA
