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Laboratory Oven Failures

I decided that it was not wisdom that enabled [poets] to write their poetry, but a kind of instinct or inspiration, such as you find in seers and prophets who deliver all their sublime messages without knowing in the least what they mean.

Socrates (469 BC - 399 BC).

Author: V. Narayan

Location: 2.1.1 Pharmaceutical Plant


In this location, the Research and Development (R&D) department also managed the Quality Assurance (QA) program. In line with QA requirements, they tested product samples by developing cultures (in Petri dishes). The process of developing cultures requires a constant temperature of about 30°C for several days. There were eight ovens in the laboratory for providing this controlled environment.

The ovens had a large cavity, about 3' wide, 3' deep and 30" high. A set of electrical heating elements along the side walls provided heat. A bimetallic thermostat turned the heating elements off when the temperature exceeded set limits. A small fan 8" in diameter was mounted at the center of the ceiling of the oven. It rotated very slowly, gently wafting the warm air from the sides down the center of the oven. The intention was to produce a toroidal flow path to help distribute the temperature uniformly in the oven (see Figures 43.1 and 43.2).

Petri dishes, about 4" in diameter, containing the culture samples were placed on wire trays. The latter allowed free flow of air. These trays could slide out once the oven door was opened. There were seven trays in each oven, spaced about 3" apart. The top tray was 9" below the oven's ceiling while the fan blades were 2" below the ceiling. In placing the dishes, the laboratory technicians took care to ensure that there was a uniform airflow around them.


326 Chapter 43

Perspective View of Oven

Figure 43.1 Perspective View of Oven

Original Air Flow Paths

Figure 43.2 Original Air Flow Paths

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