The bags make air grab sampling easy and efficient. (Nextteq photo)

Whole Air Sampling: No Pump, No Problem

Traditional grab sampling methods require supplementary devices such as electric pumps, batteries, charging devices, calibrators, tubing, connectors, and auxiliary equipment.

The collection of whole air or gas "grab samples" with commercially available gas sample bags is a widely used sampling method in fields such as environmental science and industrial hygiene, as well as in a variety of laboratory and technical applications.

The traditional grab sampling method with gas sample bags requires the use of a pump to fill the sampling bag by one of two ways. The Direct Method uses a vacuum pump to draw air from the ambient air being sampled, which then passes through the pump and is loaded into the sample bag. This method is easy to use but allows for potential cross-contamination from the inner parts of the pump fittings and any connection tubing. The Indirect Method employs a hard-walled, hermetically sealed box that is commonly referred to as a lung box. The sampling bag is fixed inside the lung box and connected to the interior fitting inlet. When the lung box is evacuated by a vacuum pump, the sample bag inflates and a sample is collected.

Both methods require supplementary devices such as electric pumps, batteries, charging devices, calibrators, tubing, connectors, and auxiliary equipment. Each method requires a skilled person to gather the sample, which can be time consuming and costly.

A new type of sampling apparatus has been introduced. The Manual Inflating Sample Bag utilizes an all-in-one design that allows a new way for a whole air grab sample to be collected directly, without any need for special equipment or expertise. Simple, intrinsically safe, and made of durable multi-layer foil, these new all-in-one sample bags are reusable and, unlike most other sample bags, can be air shipped for overnight delivery and rush analysis. The bag's durable, proprietary, multi-layer construction is ideal for stable storage of most gases. The unique construction of the sample bag includes two side panels with retractable handles made from lightweight, corrugated materials. This sample bag has the added benefit of being intrinsically safe because there are no electric components. It uses materials that help to dissipate static charge, allowing it to be used in areas with intrinsic safety requirements. Manual Inflating Sample Bags are designed to be easy to use. When the valve is opened, the user draws air in by simply pulling on the handles (bag side walls). When sampling is completed, the user closes the valve. The unique construction of the bag allows the sample bag to be easily flushed several times before sample collection, thereby allowing for equilibrium of sampled gas onto the bag interior surfaces and giving the user a more representative sample for analysis.

These bags offer flexibility in how and when the whole air or gas grab sample is performed. They can be used to collect gas or air samples rapidly and without any further preparation, allowing users to collect samples immediately if needed. Furthermore, unlike with stainless steel canisters, samples are not subject to pressure or vacuum when tested and therefore avoid the calculations and measurements required that relate to sample withdrawal and addition of dilution gas. Compared to steel canisters, shipping is inexpensive due to the light weight of the bag. They are light, convenient, and allow for rapid sampling. Once sampling is finished, the lightweight bags (approximately 100 grams) are easily transportable allowing the sample to be sent via air shipment, which is not recommended for most other bags. Experiments conducted on the bag simulating pressure changes encountered in air shipment at different pressures up to 33,000 feet (11,000 meters) showed no sample losses, no change in mechanical integrity, and no residual deformation. This allows the bag to be shipped overnight or via air shipment for situations when it is vital to have the sample undergo analysis quickly. A unique identifying number on each bag reduces the potential for errors in the chain of custody. This new collection device allows the user to collect a sample of air or gas without supplementary equipment and deliver a sample to an off-site lab within 24 hours.

If users are measuring gas or vapor concentrations with detector tubes, then multiple tests may be performed with a single bag. If testing is performed by an off-site laboratory, users still have analysis options, such as performing on-site screening measurements before shipping the sample for off-site laboratory analysis. Existing rush sample analysis can be further augmented with air delivery, which is not an option with most sample bags. Users can collect a whole air or gas grab sample more easily, faster, at less expense, and more conveniently than with traditional grab sampling methods.

This article originally appeared in the February 2016 issue of Occupational Health & Safety.

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