Fire Fighter Tools and Equipment No. 2 Questions taken from Jones & Bartlett Fundamentals of Fire Fighter Skills (3rd Edition) Progress Indicator: Question 2 of 15 2.  Which is NOT considered a limitation of pH paper? p. 527 Choices: Difficulty reading the paper if the material sampled chemically strips the paper Inability to detect the concentration of the material Need to sample distant from the material Difficulty reading the paper if the material sampled is contaminated with opaque materials