The following terms were used by NAIMA researchers to rate the degree of lung damage: in order of severity, the terms are: minimal - slight - mild - moderate - severe.

At three months, according to NAIMA's report to the EPA, the lungs of hamsters exposed to fine-diameter specialty fibers (median diameter .68 microns, median length 14.7 microns) exhibited:

• slight to mild excess in the number of pulmonary macrophages.
  
• "A number of micro granulomas and occasional multinucleated giant cells, most of which were located along the alveolar ridges of the proximal portion of the alveolar duct. There were many fibers, most of which were within these macrophages, micro granulomas and giant cells; some of the fibers appeared quite long. It was also not unusual to find fibers in macrophages just beneath the pleura."
  
• overall lung damage consistent with Wagner Grade 2 (scale of 1-8; 8 being most severe).

After five to six months exposure to the same fibers, the following was noted by NAIMA researchers:

• "While none of the hamsters showed evidence of pulmonary fibrosis at three months, and at that time were considered to be Wagner Grade 2, a majority showed a slight amount of collagen deposition after five-six months exposure in the area of the bronchioalveolar junctions. Approximately 20-30 percent of the lobules were so affected. This degree of pulmonary fibrosis qualifies the lesion as Wagner Grade 4.
  
• "A slight amount of focal collagen deposition was noted in all of the hamsters.
  
• "A minimal amount of mesothelial hypertrophy (mesothelial cells were round compared to the normal flat appearance) was noted in a majority of the animals.
  
• "Slight 'mesothelial activation,' as evidenced by cell enlargement and hyperchromatic nuclei, was observed in most of the hamsters."

Exposure to ordinary insulation fibers (median diameter .95 microns; median length 15 microns) delivered a total dose of fibers to the hamsters' lungs of less than one-third of the amount per dry lung weight compared to the special use fibers. This resulted in:

• "Slight to mild excess in the number of pulmonary macrophages
  
• "Presence of micro granulomas randomly scattered throughout the parenchyma (the essential or functional tissues of an organism, as distinguished from connective tissues or blood vessels-Webster's New World dict.), most concentrated in the area of the proximal alveoli.
  
• "Many fibers were observed, most of which were within these macrophages and micro granulomas; some of the fibers appear quite long."
  
• overall lung damage consistent with Wagner Grade 2.

Hamsters were also exposed to three different doses of amosite asbestos, with predictable results: microgranulomas, multi-nucleated cells and changes to the mesothelium, including thickening.  Collagen deposition and early stages of fibrosis was evident. The most heavily exposed animals showed significant fibrosis and were rated at Wagner Grade 4 at 3 months and Wagner Grade 5 after six months. One animal had what appeared to be an early mesothelioma. Hamsters exposed to low and medium doses of Amosite were Grade 4 after five to six months. Their lungs and pleura showed numerous granulomas and giant cells, fibers within macrophages and early signs of fibrosis.