Simplified Air Sampling Using Passive Monitors

In occupations where employees are prone to inhale chemicals, hazardous dust or metal fumes, air samples are collected to assess air quality as part of worker health and safety requirements. Active sampling is a commonly performed method where the employee wears a sampling pump with a filter while on the job. The pump sits at the waist and is connected via a tube to a filter that sits on the shirt collar. Any chemicals, dust or fumes in the air are deposited onto the filter while the employee is working; in turn, this filter is analyzed for those toxins at occupational exposure limits that are set by governing bodies such as OSHA and NIOSH. As the filter is placed close to the employee’s breathing zone, it collects an accurate representation of his or her air quality. The pump must be calibrated before sampling, and a new, clean filter must be inserted.

Disadvantages of Active Sampling

Employees who conduct active sampling often complain about having to carry around one or more of these heavy sampling pumps for the duration of their work day. In addition to the abundance of equipment that may be required for active sampling, employees are often concerned about whether the sampling equipment will arrive on time, whether everything required will be included in the shipment, and whether the pump will be properly calibrated and functioning. Furthermore, active sampling can be expensive!

Air Sampling Using Passive Monitors

Although active sampling is recommended for detecting particulates, there is another option available for gasses and vapors – collection via passive sampling. This method requires wearing a passive monitoring badge on the shirt collar; the lack of heavy equipment imposes minimal disruption onto an employee’s daily routine. As they are easy to use, especially in confined spaces, passive monitors can also facilitate full shift (or longer) sampling periods. It is important to keep in mind, however, that each passive sampler is different and the manufacturer’s instructions should be consulted for potential interferences and also for proper sampling instructions.

What You Need to Know About Passive Monitors

When sampling with a badge, there are several considerations that need to be taken into account. The first consideration is whether the badge was designed to collect the chemical of interest. The monitor must be compatible with the analyte of interest and facilitate its collection. Another consideration is whether there is enough airflow in the sampling area. If you are performing area samples in an area were the air is stagnant, passive badges are not recommended. Furthermore, if you are sampling for multiple compounds using an organic vapor badge, it is important to make sure that the analytes are compatible. Lastly, it is crucially important to be aware of the uptake rate (diffusion rate) of the particular monitor and the analyte of interest. The uptake rate – the rate that the analyte of interest will be absorbed into the monitor – is dependent on the diffusion path length and the size of the openings that allow air to be exposed to the monitor. Smaller holes and longer diffusion paths will result in a lower intake rate than larger holes with short diffusion paths. This diffusion rate is used to calculate the airborne concentration, as well as the reporting limit, expressed in an airborne concentration. If the laboratory reporting limit (in µg) and the uptake rate are known, sampling time can be determined in order to meet the standard criteria. Diffusion rates, if not published by the manufacturer, can often be acquired by calling the media supplier’s technical support line.

Passive Monitor Analysis

Bureau Veritas is set up to analyze many gasses and/or vapors using passive monitors (see table 1 for most common analyses). Our Industrial Hygiene laboratory provides the badges below at no charge with a couple of exceptions and as long as they are sent back to the laboratory for analysis. If you have sample questions, or are interested in a passive badge not included in the table, please contact our client services team.

Table 1: Common Methods of Analysis Using Passive Monitors