IMPACT RESISTANCE OF THIN CR39 LENSES UNDER THE BALLISTIC TEST

Title IMPACT RESISTANCE OF THIN CR39 LENSES UNDER THE BALLISTIC TEST
Author, Co-Author B. Chou, Weslie L. Fong
Topic
Year
1992
Day
Sunday
Program Number
Poster 54
Room
Great Hall
Affiliation
Abstract Two of the principal factors in worker non-compliance with safety regulations requiring use of protective eyewear are the discomfort and poor cosmesis of thick (3 mm) industrial lenses. It has been argued that use of thinner protective lenses in occupational eyewear may increase compliance, if it can be shown that eye safety is not greatly compromised. The impact resistance of thin CR39 spectacle lenses of nominal thicknesses 1.3, 1.4 1.7 mm was studied using a ballistic test. Lenses were ordered from a single custom optical laboratory to ensure uniform handling, then edged and mounted in a metal industrial frame. Completed spectacles were placed on a headform for ballistic testing using a 6.5 mm steel ball propelled from an airgun. Test sample groups of 10 lenses each were subjected to (i) a single impact at the geometrical center by a ball travelling at 18.0 m/s, and (ii) 50 consecutive impacts at the same location at 18 m/s, or (iii) a single impact by a ball travelling at 46.5 m/s. All lenses passed the single impact test at 18 m/s. One lens of 1.7 mm thickness cracked after 29 impacts at 18 m/s; all other lenses survived 50 impacts without visible damage. All 1.3 mm lenses failed the high speed test at 46.5 m/s, while 70% of the 1.4 mm lenses and 50% of the 1.7 mm lenses failed. Our findings show that thin CR39 lenses provide impact protection from small blunt missiles travelling at moderate speed, and that they are durable under repeated low energy impact. Such lenses may provide adequate eye protection in certain industrial settings, but do not provide adequate protection from small high speed projectiles. Thicker CR39 lenses must be used whenever there is a significant risk of worker exposure to small high speed missiles in the workplace.
Affiliation of Co-Authors
Outline