Clean room fire simulation

Details Clean room fire simulation Clean room fire simulation

2003-03-06

2004-08-24

Raevis, Robert R. (Department: 2856)

Measuring and testing

Simulated environment

Reexamination Certificate

active

06779413

ABSTRACT:

This invention relates to clean room fire simulation for the purpose of measuring damage to material in the clean room due to a clean room fire as a function of the material of the fire source and contaminant concentration.
A fire in a clean room, with downcast air flow from ceiling toward the floor, usually involves two contamination zones of combustion products that can damage process equipment and product, primarily by particle deposition and corrosion. A primary contamination zone, where the smoke contaminant concentration is very high, is in the immediate volume surrounding a fire. In the primary contamination zone the combustion products come into contact with the material or equipment being damaged without the combustion products being filtered. The primary contamination zone is confined by the walls of the clean room bay, or if the fire is in a large clean room bay, the primary zone extends to a surrounding umbrella-shaped boundary created by the interaction of the downcast flow in the clean room bay with the fire. A secondary contamination zone consists of a clean space surrounding the primary zone. The secondary contamination zone receives fire contaminants circulating from the primary zone but the combustion products containing the contaminants will have passed through high-efficiency particulate air filters (HEPA) or ultra-low penetration air filters (ULPA). The filters will remove most of the particulate contamination as well as gases adhering to the particles, but residual contamination in the secondary contamination zone may still be capable of causing damage. Currently there is no method or apparatus which will directly evaluate the damage potential in either the primary contamination zone or the secondary contamination zone for fires in clean room facilities and there is a need to make such evaluations as a function of the different types of materials which may be burned in a clean room fire as well as the contamination concentration in the combustion products.
SUMMARY OF THE INVENTION
In accordance with the invention, a simulator is provided comprising a burn cell and a secondary exposure cell representing the secondary contamination zone for a clean room fire. The cells may be cubical in shape and are reduced in size relative to the clean room in which a fire is being simulated. A clean room filter, such as a HEPA or ULPA filter, caps each cell and both cells have perforated floors. A fire burning a selected candidate material is provided in the burn cell and the material or equipment to be evaluated for damage is provided in the secondary exposure cell. An air mover, such as a fan or jet pump, is connected by ducting to the cells to circulate combustion products from the fire in the burn cell through the filters, downwardly through both cells, and out through the perforated floors in the cells. The downward flow through the cells simulates the downward flow that exists in a clean room. After a predetermined period allowing the combustion products from the burn cell to circulate through both the burn cell and secondary exposure cell, the damage to the material or equipment in the secondary exposure cell is evaluated to provide a determination of the damage in a secondary contamination zone of a clean room fire from the burning of the candidate material. Equipment and material could also be placed in the bum cell to evaluate the damage in the primary contamination zone of a clean room fire, but exposure conditions in the burn cell will be quite nonuniform.
To provide simulation to measure damage in a primary contamination zone of a clean room fire, the gases containing the combustion products flowing through the perforated floor of the burn cell are directed by the ducting to a test loop in which test material or equipment to be evaluated for damage is placed. The test loop contains an orifice and a mixing duct to provide a uniform exposure and contaminant concentrations at the test material or equipment in the mixing duct. The resulting damage to the material or equipment in the mixing duct will be uniform and will be an accurate indication of the damage that would occur in a primary contamination zone of a clean room fire burning the candidate material.


REFERENCES:
patent: 6174469 (2001-01-01), Ganan-Calvo

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