Fabric sheath for ventilation and laminar flow hood

Details Fabric sheath for ventilation and laminar flow hood Fabric sheath for ventilation and laminar flow hood

1998-10-26

2000-09-05

Joyce, Harold

Ventilation

Clean room

454296, F24F 13072

Patent

active

061134864

DESCRIPTION:

BRIEF SUMMARY
The present invention relates in a general manner to the close protection of a work station located in a contaminated atmosphere, and more particularly to a device for the close protection of products sensitive to contamination by airborne contaminants, said products being positioned on a work surface.
The present invention relates more particularly to a sheath for the close protection of the conveyance of sensitive products by the diffusion of a stream of sterile air, especially in an approximately vertical direction, said sheath being formed by an impermeable wall and a porous wall extending longitudinally parallel to the axis of the sheath, said sheath defining a sterile-air supply duct.
The invention also relates to a washable or disposable laminar-flow hood, as well as to a device for the close protection of a wide work surface comprising such sheaths.
The problem of protecting work stations from air contamination arises especially in the agro-foodstuffs industry, the pharmaceutical industry or in the hospital environment.
In general, in order to solve this type of problem, the work stations are located in rooms called "clean" rooms in which the air is filtered and treated so that the amount of dust lies below a controlled permissible threshold subject to strict regulations.
In addition, the air which circulates in these clean rooms is often regulated at a low temperature.
Staff having to work in such work stations must be clad in specialized suits which are difficult to get into and to wear.
The close protection of each individual work station is one way of solving the aforementioned drawbacks.
However, this close protection must take account of the fact that the staff working at these work stations must handle products sensitive to air contamination.
Likewise, it is undesirable to provide mechanical protection systems, for example doors, since opening and closing them causes flow disturbances incompatible with maintaining the sterility. This is why a sterile-atmosphere confining and maintaining means using only streams of air has already been described.
Thus, confining devices have been developed which are intended to ensure close protection of a particular volume with the aid of a slowly diffusing vertical stream of air, said stream of air being bordered by two more rapid jets of air which constitute the external means of protecting the volume.
This type of close protection may be implemented using various embodiments, especially box-type systems with diffusion grilles which make it possible to generate the streams of air with the appropriate speeds. Such a system is described in document U.S. Pat. No. 3,776,121; it comprises an air outlet plate pierced with holes, the surface area of which increases from the center to the periphery in order to generate a central slowly-diffusing stream of air bordered by rapidly diffusing streams of air.
However, these quite heavy devices are expensive, but above all are quite difficult to clean and not very flexible, especially when it is a question of providing close protection to a conveyance line following a sinuous path.
This is why the present invention proposes close-protection devices employing one or more textile sheaths capable of generating the desired gas flows. It is in principle possible to produce such a device with the aid of a textile sheath comprising a central diffusing part bordered longitudinally on each side by two slots.
In practice, the Applicant has observed that such a sheath, having a perimeter of 1.885 m, consisting, for example, of a central porous part corresponding to 25% of the perimeter (i.e. 0.47 m) bordered by two slots, each 15 mm in width (i.e. 0.016% of the perimeter in respect of the two slots), though giving certain useful results, does not, however, give optimum results. This is because the respective velocities of the rapid and slow streams of air are not constant along the sheath.
It would be possible to increase the pressure level inside the sheath. However, this would cause much too high a velocity increase in the slots

REFERENCES:
patent: 3719136 (1973-03-01), Criddle
patent: 3776121 (1973-12-01), Truhan
patent: 4009647 (1977-03-01), Howorth

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