Methods Evaluation, Purpose Collecting AIR Samples

Threshold Limit Value-Short- Term Exposure Limit (TLV-STEL): The 15-minute TWA concentration which should not be exceeded at any time during a workday even if the 8- hour TWA is within the TLV-TWA. Exposure above the TLV-TWA up to the STEL should not be longer than 15 minutes and should not occur more than four times per day with at least 60 minutes in between exposures in this range.

Threshold Limit Value-Ceiling (TLV-C): The concentration that should not be exceeded during any part of the working exposure.

OSHA Limits vs ACGIH Guidelines: OSHA limits are legally enforceable, whereas ACGIH limits are guidelines. In most cases, the ACGIH guidelines are the same or lower than OSHA limits (there are a few exceptions). When the values are not the same, it is prudent to follow the lower, more conservative value.

Examples:

Chemical	OSHA	ACGIH
Chemical	PEL 8-hour	TLV 8-hour
	PEL 8-hour	TLV 8-hour
Acetic acid	10 ppm	10 ppm

Ammonia	50 ppm	25 ppm

Formaldehyde	0.75 ppm	0.3 ppm
		(ceiling)

Sulfur dioxide	5 ppm	2 ppm

METHODS OF

EVALUATION

THE PURPOSE OF

COLLECTING AIR

SAMPLES

Air samples are sometimes collected to evaluate potential worker exposure levels for comparison to published exposure standards or guidelines. The purpose of the

measurement may vary depending on whether you are interested in short-term exposure, full shift exposure, or the exposure incurred during a specific step or process. The measurements represent a sampling of the actual working conditions at the time of sampling. Generally, the more sampling data that are available for a certain job/process/ task under a variety of conditions, the better understanding and confidence you will have in the exposure measurements during that process. As illustrated in Figure 1, actual exposure can vary substantially during the day. In some cases, full-shift monitoring may be the goal while in others, the goal may be to understand short- term exposure.

Figure 1

Typical Exposure Scenario

				Actual
Concentration (ppm)		OSHA PEL		8-hr
				Avg.

8am	10am	Noon	2pm	4pm

Basic Definitions

Sensitivity or Precision: how

reproducible is the sampling method.

Accuracy: how close to the true value is the sampling method.

MEASUREMENT

TECHNIQUES

Direct Reading

These are measurement techniques that can immediately indicate the concentration of aerosols, gases, or vapors by some means such as a dial or meter or noting the color change of an indicator chemical.

Colorimetric Detector Tubes Several colorimetric, direct reading detector tubes are useful for quick assessments of airborne contaminants associated with photographic processing. A special pump draws a specific volume of room air through a detector tube. If the contaminant is present, a color change occurs along the length of the tube that is directly proportional to the concentration of the contaminant in the air. Tubes are available for acetic acid, sulfur dioxide, ammonia, and many other gases and vapors. The tubes are easy to use and generally have an accuracy of ± 25%. Other chemicals in the air may interfere with the accuracy and sensitivity of the tubes.

Indoor Air Quality and Ventilation in Photographic Processing Facilities • J-314(ENG)