Negative pressure containment

Local ventilation Contain and exhaust hazardous substances. Use properly designed hoods. Use hoods for charging and discharging. Use ventilation at drumming station. Use local exhaust at sample points. Keep exhaust systems under negative pressure. 

A second approach is to obtain (extract) water as it naturally occurs in soil pores. Typically, a porous ceramic cup (other materials are available) is placed in an unsaturated soil, either in the field or laboratory. A vacuum is applied (slightly more negative pressure than the water in the soil pores see also Chapter 5) to the ceramic cup via tubing to move water into a receiving container. This water can be analyzed for all its constituents. A reason for obtaining this type of soil water sample is to analyze it for one specific constituent such as a herbicide, insecticide, or pollutant. Water extracted in this way may also better represent the concentration of the analyte of interest to which plant roots are exposed. 

Positive-pressure areas should be used to process sterile products but negative pressure in specific areas at point of exposure of pathogens is acceptable for containment reasons. 

Briggs (B12) was able to subject water at room temperature to a negative pressure of nearly 270 atm. The experimental technique consisted of spinning a horizontal glass tube ( scrupulous cleanliness is necessary ) about a vertical axis located at its center. The tubing contained the liquid and was open at both ends. The centrifugal force needed to break the liquid column was observed. The experimental results are shown in Fig. 24. 

Heating of radioactive solutions, particularly under elevated pressure (e.g., steam sterilization), is also a matter of safety. In order to avoid any contaminated air to escape if a container or a seal is broken, autoclaves used for radioactive solutions should be placed inside negative-pressure sealed units. Autoclaves used for sterilizing high-energy y-emitting radiopharmaceuticals should in addition be supplied with proper lead shielding. 

When entering agent contaminated operational areas, isolation of clean areas from those containing released agent is assured by means of this negative pressure and by the use of air locks. 

Vapor containment will consist of a facility designed to provide negative pressure, controlled air flow, and walled or multiple walled enclosures which will contain any detectable quantities of agent released. 

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