Test chambers recovery

Door-opening tests to determine chamber recovery time... 

A second formaldehyde recovery study by Georgia Tech in their large scale test chamber agrees very well to study 1. The Georgia Tech test chamber is modeled after the Georgia-Pacific chamber used in study 1. In a to be released report (21 ), a summary of their second study is as follows ... 

Georgia-Pacific Recovery Studies. For us to perform our own recovery study, we refined and developed a syringe pump method for generating formaldehyde concentrations within our large scale test chamber. This method was originally created by Mr. Bill Lehnman of Weyerhaeuser, Tacoma, Washington (22). 

Chamber measurement Supply air quality Background concentration Sink effects/recovery Air exchange ratio Air tightness of the environmental test chamber Internal air mixing Air velocity Accuracy of temperature, RH and air exehange ratio Product loading factor... 

Long-term respiratory exposures are usually patterned to projected industrial experience, giving the animal a daily exposure 6 hours after equilibrium of chamber concentrations, for 5 days a week (intermittent exposure) or 22 to 24 hours of environmental exposure per day, 7 days a week (continuous exposure), with 1 hour for feeding and maintaining the chambers. In both the cases, the animals are usually exposed to a fixed concentration of test materials. A major difference to consider between intermittent and continuous exposure is that in the former there is a period of 17 to 18 hours in which animals may recover from the effects of daily exposure, and an even longer recovery period during weekends. 

A recent review [73] describes the various animal models used to mimic the different aspects of this disease. For KCAs, the in vivo models employed have generally been bronchoconstrictor in nature, where test compounds have been examined for their ability to prevent or reverse an induced bronchoconstriction. This can be achieved in several ways, the simplest being the respiratory embarrassment model, where a guinea-pig is exposed to a concentration of a bronchoconstrictor that causes dyspnoea. The KCAs may be tested by the oral route for their ability to attenuate the onset of dyspnoea. Even in the control animals, in which dyspnoea leads to rapid collapse, removal of the animals from the chamber and away from the bronchoconstrictor agent, allows a full recovery [74]. Various other ways of inducing bronchoconstriction in conscious animals are available, one of the... 

Formaldehdye generation and recovery studies 3.) Air exchange measurement techniques 4.) Preconditioning of test boards 5.) Temperature effect on chamber formaldehyde concentrations 6.) Relationship of popular quality control test methods to the large chamber 7.) Loading, air exchange rate, and wood product combination effects on chamber formaldehyde concentrations 8.) Chamber Round Robin studies between Georgia-Pacific s chamber and other outside lab chambers 9.) Chamber concentrations and its relationship to actual field measurements. 

Available data based on limited exposure tests in chambers and comparisons with pumped sampling methods in the laboratory and field show the techniques can be used to determine mean concentrations of VCX3s over periods of a day to several weeks for fixed site and personal monitoring. Problems of poor recovery at the desorption stage and possible losses by back diffusion means the investigator needs to consider carefully the choice of sampler and, in the case of thermally desorbable tubes, the optimum sorbent for the investigation. 

This sink effect caused by the sample is always of importance in any examination in a chamber, and it cannot be avoided. Thus, it is of fundamental significance that an empty chamber guarantees as good a recovery as possible. For selected VOCs in a concentration range which is typical for emission examinations, the recovery is determined by one of the following procedures. Test gases with a known concentration of VOCs are introduced into the chamber, or small permeation or diffusion tubes are placed in the test cell. At the air outlet of the empty chamber the VOC concentration is measured in each case and it is then compared with the theoretical nominal value. The recovery for target VOCs should be > 80 %. 

A strain-controlled or fully confined recovery test was conducted. It started immediately after completion of the programming with the same loading device and environmental chamber. The chamber was heated at a ramp rate of 0.6°C/min. The heating was continued until the temperature starting the programming (71 °C or 79 °C) was reached. After that, the temperature was maintained constant for several hours and the stress was continuously recorded. This process was stopped when further stress recovery was negligible. 

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