These Safety Filled thermometers are ideal for special applications with limited space of immersion. Biodegradable liquid is safe for a working environment. Permanently fused markings. Safety Filled Thermometers protect you and the environment from the hazards of mercury. The liquid in the thermometer is both safe and biodegradable, eliminating the danger of mercury spills and disposal problems in the classroom. The liquid is colored with a non-toxic blue dye that minimizes reading errors with its high visibility. Calibrated with NIST (NBS) Standards, thermometers include a Statement of Accuracy and non-roll ring tops.