# NIOSH Pocket Guide to Chemical Hazards
Silicon | CAS 7440-21-3
Si | RTECS VW0400000
Synonyms & Trade Names Elemental silicon [Note: Does not occur free in nature, but is found in silicon dioxide (silica) & in various silicates.] | DOT ID & Guide 1346 170 (amorphous powder)
Exposure Limits | NIOSH REL: TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
OSHA PEL†: TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)
IDLH N.D. | Conversion
Physical Description Black to gray, lustrous, needle-like crystals. [Note: The amorphous form is a dark-brown powder.]
MW: 28.1 | BP: 4271°F | MLT: 2570°F | Sol: Insoluble
VP: 0 mmHg (approx) | IP: NA |  | Sp.Gr(77°F): 2.33
Fl.P: NA | UEL: NA | LEL: NA | MEC: 160 g/m3
Combustible Solid in powder form.
Incompatibilities & Reactivities Chlorine, fluorine, oxidizers, calcium, cesium carbide, alkaline carbonates
Measurement Methods NIOSH 0500, 0600
Personal Protection & Sanitation Skin: No recommendation Eyes: Prevent eye contact Wash skin: No recommendation Remove: No recommendation Change: No recommendation | First Aid (See procedures) Eye: Irrigate immediately Breathing: Fresh air Swallow: Medical attention immediately
Respirator Recommendations To be added later
Exposure Routes inhalation, ingestion, skin and/or eye contact
Symptoms Irritation eyes, skin, upper respiratory system; cough
Target Organs Eyes, skin, respiratory system
See also: INTRODUCTION