# NIOSH Pocket Guide to Chemical Hazards
Silica, amorphous | CAS 7631-86-9
SiO2 | RTECS VV7310000
Synonyms & Trade Names Diatomaceous earth, Diatomaceous silica, Diatomite, Precipitated amorphous silica, Silica gel, Silicon dioxide (amorphous) | DOT ID & Guide
Exposure Limits | NIOSH REL: TWA 6 mg/m3
OSHA PEL†: TWA 20 mppcf (80 mg/m3/%SiO2)
IDLH 3000 mg/m3 | Conversion
Physical Description Transparent to gray, odorless powder. [Note: Amorphous silica is the non-crystalline form of SiO2.]
MW: 60.1 | BP: 4046°F | MLT: 3110°F | Sol: Insoluble
VP: 0 mmHg (approx) | IP: NA |  | Sp.Gr: 2.20
Fl.P: NA | UEL: NA | LEL: NA |
Noncombustible Solid
Incompatibilities & Reactivities Fluorine, oxygen difluoride, chlorine trifluoride
Measurement Methods NIOSH 7501
Personal Protection & Sanitation Skin: No recommendation Eyes: No recommendation Wash skin: No recommendation Remove: No recommendation Change: No recommendation | First Aid (See procedures) Eye: Irrigate immediately Breathing: Fresh air
Respirator Recommendations NIOSH Up to 30 mg/m3: (APF = 5) Any dust and mist respirator Up to 60 mg/m3: (APF = 10) Any dust and mist respirator except single-use and quarter-mask respirators/(APF = 10) Any supplied-air respirator Up to 150 mg/m3: (APF = 25) Any supplied-air respirator operated in a continuous-flow mode/(APF = 25) Any powered, air-purifying respirator with a dust and mist filter Up to 300 mg/m3: (APF = 50) Any air-purifying, full-facepiece respirator with a high-efficiency particulate filter/(APF = 50) Any supplied-air respirator that has a tight-fitting facepiece and is operated in a continuous-flow mode/(APF = 50) Any powered, air-purifying respirator with a tight-fitting facepiece and a high-efficiency particulate filter/(APF = 50) Any self-contained breathing apparatus with a full facepiece/(APF = 50) Any supplied-air respirator with a full facepiece Up to 3000 mg/m3: (APF = 1000) Any supplied-air respirator operated in a pressure-demand or other positive-pressure mode Emergency or planned entry into unknown concentrations or IDLH conditions: (APF = 10,000) Any self-contained breathing apparatus that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode/(APF = 10,000) Any supplied-air respirator that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode in combination with an auxiliary self-contained positive-pressure breathing apparatus Escape: (APF = 50) Any air-purifying, full-facepiece respirator with a high-efficiency particulate filter/Any appropriate escape-type, self-contained breathing apparatus
Exposure Routes inhalation, skin and/or eye contact
Symptoms Irritation eyes, pneumoconiosis
Target Organs Eyes, respiratory system
See also: INTRODUCTION