Process Control in the Darkroom CONT.

T.O. 33B-1-1 1-73 1.9.2.7 NOTE It is extremely important that the film used for these tests never be exposed to safelight prior to the test. Therefore, if a film cassette is used, it SHALL be loaded in total darkness. Safelights for darkroom operation, contrary to their name, contribute to unwanted densities (fog) on radiographic film. To overcome this problem, the length of time that undeveloped industrial radiographic film can safely be exposed to the level of safelight within a specific darkroom SHALL be determined. This time period is much shorter for exposed film than for unexposed. The reason for this time difference is that exposed film is approximately five times more susceptible to fog caused by safelight than film that is unexposed. The safelight fog evaluation procedure consists of two tests, the individual safelight test and the collective safelight test. These tests have a requirement to be performed separately or jointly depending upon the circumstances. The circumstances when both tests SHALL be performed are: 1) initial safelight evaluation for in-use or new darkroom facility and 2) when the periodic collective safelight tests results are unacceptable. The circumstances when the individual safelight test SHALL be performed on a single or, if the requirement dictates, all safelights are: 1) initial test, which includes all safelights; 2) a newly installed fight; 3) if any changes are made to existing lights such as bulbs, filters, position, and reflecting versus direct light function; 4) whenever filters are suspect of fading and to determine the adverse effects of crazing, scratches, and cracks; or 5) whenever a light is suspect of producing excessive safelight fog. The circumstances when the collective safelight test SHALL be performed are: 1) during the periodic requirement (safelights filters deteriorate with use. The rate of deterioration is dependent on their age, amount of use and amount of heat generated by its bulb. Therefore, a periodic test schedule SHALL be established to collectively test safelights for film fog, dependent upon their use. This test cycle SHALL not exceed one year); 2) repositioning of safelights; 3) reestablishing undeveloped film handling area; and 4) installing additional safelights. The materials and procedure that SHALL be used to establish the maximum safelight exposure period is as follows: a. For the initial safelight evaluation radiographically expose an individual sheet of Class 4 radiographic film for each safelight that is in the dark room plus an additional sheet to approximately a 1.5 (± 0.2) HD units overall constant density. For example, if there are three safelights in the darkroom expose four separate sheets of film individually. In the case where only the individual safelight test is being performed, only radiographically expose the number of films that correspond to the number of safelights that are to be tested. If only the collective test is to be performed only radiographically expose one film. Each film that is radiographically exposed, to perform the individual or collective safelight tests, SHALL be identified so as to identify the specific safelight it was used to test or if it was used to perform the collective safelight test. b. To perform the individual safelight test, turn off, or remove, the bulbs from all the safelights with the exception of the safelight to be tested. During the initial safelight evaluation each safelight SHALL be tested individually and collectively. c. Turn off the safelight to be tested and ensure the darkroom is void of all ambient light. d. While all safelights are off, and in total darkness, remove the radiographically exposed film from its envelope/cassette. Position the exposed film in direct line and perpendicular with the safelight's filter, at a maximum distance of four feet unless the distance between the normal working level and safelight is greater than four feet, in which case the test film should be placed at this measurement. e. Cover the entire test film with an opaque Material, such as cardboard. f. Turn-on the safelight to be tested.