1.   Contamination found in samples from individual homes does not mean the entire system is contaminated.

2.   In any event, by midday officials said there was no sign that the ventilation system had been contaminated.

3.   The bank must make sure its systems are not contaminated by computer errors made by other organizations.

4.   When a compressor goes, the whole system often becomes contaminated with little particles of metal.

5.   Plant officials had first said the water filtration system was leaking, then they said the system had been contaminated by radioactive dust.

6.   Theories include that dead dogs found in waterways leading to a water treatment plant contaminated the system.