ERPG-3: 25 ppm (137.5 mg/m3)
25 ppm is the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects.
ERPG-2: 3 ppm (16.5 mg/m3)
3 ppm is the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious adverse health effects or symptoms that could impair an individual’s ability to take protective action.
ERPG-1: 1 ppm (5.5 mg/m3)
1 ppm is the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 hour without experiencing other than mild, transient adverse health effects or without perceiving a clearly defined objectionable odor.
Update 11-8-2022
Author: D. Kelly
I. IDENTIFICATION
Chemical Name: Trichlorosilane
Synonyms: Silicon Trichloride, Silicon Chloroform
CAS Number: 10025–78–2
DOT Number: UN1295
Molecular Formula: HCl 3Si
Structural Formula:
II. CHEMICAL AND PHYSICAL PROPERTIES (General Electric 1994)(USCG 1991)
Physical State and Appearance: Colorless, fuming liquid
Odor Description: Sharp, acidic, suffocating odor
Odor Threshold: No data available
Molecular weight: 135.5
Conversion Factors: 1 ppm = 5.5 mg/m3; 1 mg/m3 = 0.18 ppm
Melting point: -127°C(19720°C (68°F) at 760 mmHg
Boiling Point: 32°C (90°F) at 760 mmHg
Vapor Pressure: 493 mmHg at 25°C (77°F)
Saturated Vapor Concentration: 649,000 ppm at 25°C(77°F)
Vapor Density (Air = 1): 4.7
Specific Gravity: 1.34
Flash Point (closed cup): 14°C
Flammability Limits: LEL = 7%; UEL = 83%
Autoignition Temperature: 182°C (360°F)
Solubility in water: Decomposes in water
Stability and Reactivity: Reacts vigorously with water, yielding hydrogen chloride.
III. ANIMAL TOXICICITY DATA
A. Acute Toxicity and irritancy (<5 days)
1. Oral Toxicity
Male Rats: LD50 = 1030 mg/kg (gavage: 25% solution in corn oil) (Smyth et al 1949)
2. Eye Irritation
In a study with rabbits, 0.005 mL of 5% in propylene glycol undiluted trichlorosilane placed in the conjunctival sac caused 63%–87% necrosis in treated rabbits. (Smyth et al 1949)(Carpenter et al 1946)
3. Dermal Toxicity
a. Irritation
Undiluted trichlorosilane applied to the intact skin of rabbits was a corrosive irritant, rapidly causing erythema and a trace of capillary injection. (Smyth et al 1949) Trichlorosilane caused erythema in the rabbit belly vesicant test. (Union Carbide Corporation 1986)
b. Absorption – No data located
c. Sensitization – No data located
4. Inhalation Toxicity
In the nose-only inhalation study summarized in Table 1(Dow Corning Corporation 1987), clinical signs included respiratory difficulties, loss of nasal septum, corneal opacity, and ocular discharge. At necropsy, gas-distended intestinal tract and apparent hemorrhaging in the lungs were observed. A concurrent study with rats similarly exposed to hydrogen chloride vapor showed an LC50 of 8800 ppm. This value for HCl is approximately 3 times the result for trichlorosilane (TCS) supporting the hypothesis that the toxicity of TCS Is due mainly to the formation of HCl thru the hydrolysis of TCS forming 3 moles of HCl per TCS molecule.
Table 1. Trichlorosilane Acute Inhalation Lethality
| Sex/Species | Conc (ppm) | Time (Hrs) | Lethality | Analysis | Other | Reference |
|---|---|---|---|---|---|---|
| M Rat | 500 | 4 | LCLO | No Info | (Union Carbide 1979) | |
| M Rat | 1000 | 4 | 3/6 | Nominal | (Smyth et al 1949) | |
| *Rat | 995 | 1 | 0/6 | No Info | (Nachriener and Dodd 1986) | |
| *Rat | 2340 | 1 | LC50 | No Info | (General Electric 1994)) | |
| M-F Rat | 2767 | 1 | LC50 | Analyzed | Nose-Only | (Dow Corning 1987) |
| *Mouse | 270 | 2 | LC50 | Analyzed | (Izmerov et al 1982) |
(*Sex not specified)
B. Subchronic Toxicity (5-days to 6-month studies)
Rats of both sexes were exposed to 0, 25, 50, or 100 ppm trichlorosilane, 6 hr/day 5 days/week for 9 exposures. In all exposed groups, respiratory irritation, depressed body weight gain, increased lung weights, rhinitis, upper respiratory hemorrhage, and pulmonary necrosis were noted. Approximately 75% of the rats exposed to 100 ppm died (time of deaths not stated). Alveolar histiocytosis and pneumonitis were noted in rats exposed to 50 or 100 ppm. Irritation was noted in all exposed rats. (Dodd et al 1989)
C. Chronic Toxicity / Carcinogenicity (> 6-month studies)
No data available.
D. Reproductive/Developmental Toxicity
No data available
E. Genotoxicity/Mutagenicity
Trichlorosilane was not considered a mutagen, with or without S-9 metabolic activation, when tested in the Ames assay in Salmonella typhimurium strains TA-98, TA-100, TA-1535, TA-1537, and TA-1538. (Isquith and Miller 1981)
F. Metabolism/Pharmacokinetics
No data available.
IV. HUMAN EXPERIENCE
A. Odor Data
Trichlorosilane exhibits a sharp odor similar to hydrogen chloride. The odor threshold in humans has not been determined, but it would be expected to be very similar to that of hydrogen chloride. The irritation data for hydrogen chloride is summarized in Table 1.
Table 2. AIHA Hydrogen Chloride ERPG (AIHA 2016)
| Concentration (ppm) | Duration | Comments |
|---|---|---|
| 0.26 | --- | Minimum concentration detected by most sensitive volunteer. |
| 5-10 | --- | Immediately irritating. |
| 10 | --- | Concentration said to be detectable by all exposed volunteers as irritating, but some tolerance possible. |
| 10 | Prolonged | Recommended maximum acceptable concentration. |
| 35 | Short | Irritation of the throat. |
| 10-50 | Few hours | Maximum tolerable concentration. |
| 50-100 | 1-hour | Maximum tolerable concentration. |
| >1000 | Short | Life-threatening. |
B. Toxicity Data
No trichlorosilane toxicity data on humans has been reported.
C. Workplace Experience
An accident involving a truck carrying trichlorosilane, silicon tetrachloride, and sodium hydroxide resulted in the exposure of three police officers investigating the incident. Within a few hours, they all developed a condition described as reactive airway dysfunction syndrome, characterized by a persistent bronchial hyperactivity and asthmatic symptoms. It was not possible to identify the responsible agent. (Promisloff et al 1990)
In another report, delayed eye effects in a subject presumably exposed to trichlorosilane were described. The first symptom evident in the victim some 3 hrs after the exposure was visual impairment (the street lights appeared to be dim). An hour later, pain was reported. The authors suggested that the apparent visual impairment was due to sloughing corneal epithelial cells and the pain was due to the then exposed nerve endings. (Union Carbide 1994)
D. Epidemiology
No data located
V. CURRENT EXPOSURE GUIDELINES
Neither an ACGIH® Threshold Limit Value (TLV®) nor an OSHA permissible exposure limit (PEL) has been established for trichlorosilane.
The AIHA® WEEL is 0.5 ppm (ceiling). (AIHA 1998) It is generally held that workers are protected by maintaining trichlorosilane concentrations below the irritation concentration for hydrogen chloride.
A. ACGIH TLV and OSHA PEL for Hydrogen chloride
The ACGIH® TLV® for hydrogen chloride is 2 ppm ceiling limit, which is interpreted as low enough to prevent toxic injury but possibly irritating. (OSHA 1990)(ACGIH 2003)
The OSHA PEL for hydrogen chloride is a 5 ppm ceiling limit. (OSHA 1990)
B. The National Research Council (NRC) EEGL for Hydrogen Chloride
The NRC has set the following emergency exposure guidance levels (EEGLS) for hydrogen chloride; 10 min – 100 ppm; 1 hr – 20 ppm; and 24 hr – 20 ppm. These levels are defined “as a concentration of a substance in air (as a gas, vapor, or aerosol) that will permit continued performance of specific tasks during rare emergency conditions lasting for periods of 1–24 hours. Exposure at an EEGL might produce reversible effects that do not impair judgment and do not interfere with proper response to the emergency.” (NRC 1987)
C. AEGL for Hydrogen Chloride
The EPA, using HCl formation as a rationale, proposed final one-hour trichlorosilane AEGL values based on the existing AEGL values for HCl using a molar adjustment factor of 3 (NAS 2012):
AEGL-3 33 ppm
AEGL-2 7.3 ppm
AEGL-1 0.6 ppm
D. ERPG for Hydrogen Chloride
The AIHA ERPGS for HCl (AIHA 2016) are:
ERPG–3: 150 ppm
ERPG–2: 20 ppm
ERPG–1: 3 ppm.
VI. RECOMMENDED ERPGS™ AND RATIONALES
The rationale for all three trichlorosilane ERPGs is based on the same set of considerations. It is noted that the toxic effects of trichlorosilane are similar in many respects to those of its hydrolysis product, hydrogen chloride. Both chemicals cause severe burns by all routes of exposure. In addition to the 1-hr LC50 study with trichlorosilane, a concurrent study with rats similarly exposed to hydrogen chloride vapor showed an LC50 of 8800 ppm. This value for HCl is approximately 3 times the result for trichlorosilane (2767 ppm), supporting the hypothesis that the toxicity of TCS Is due mainly to formation of HCl thru the hydrolysis of TCS forming 3 moles of HCl per TCS molecule and assuming the contribution from other reaction products to be negligible during this short exposure period.
On the basis of HCl formation, the projected ERPG values for trichlorosilane would be one third of the HCl ERPG values: ERPG–3 = 50 PPM; ERPG–2 = 7 ppm; and ERPG–1 = 1 ppm. However, a prominent feature of trichlorosilane is a significant latent effect on the eyes. (Union Carbide 1994) It is therefore considered prudent to further divide the ERPG–3 and ERPG–2 levels by 2, resulting in: ERPG–3 = 25 ppm; ERPG–2 = 3 ppm; and ERPG–1 = 1 ppm. These levels should be protective for sensitive members of the population.
A. ERPG – 3: 25 ppm (137.5 mg/m3)
25 ppm of trichlorosilane is the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 hr without experiencing or developing life-threatening health effects.
B. ERPG – 2: 3 ppm (16.5 mg/m3)
3 ppm of trichlorosilane is the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 hr without experiencing or developing irreversible or other serious adverse health effects or symptoms that could impair an individual’s ability to take protective action.
C. ERPG – 1: 1 ppm (5.5 mg/m3)
1 ppm of trichlorosilane is the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 hr without experiencing or developing effects other than mild transient health effects or perceiving a clearly defined objectionable odor.
VII. HISTORY OF TRICHLOROSILANE ERPGS
First Published in 1998:
ERPG-1: 1ppm, ERPG-2: 3 ppm, ERPG-3: 25 ppm
Updated in 2010, Values unchanged
Updated in 2022, Values unchanged
VIII. REFERENCES
ACGIH®: Hydrogen Chloride: TLV® Chemical Substances 8th Edition Documentation. 2003
American Industrial Hygiene Association® (AIHA®): Emergency Response Planning Guidelines—Hydrogen Chloride. Fairfax, VA: AIHA, 2016.
American Industrial Hygiene Association® (AIHA®): Workplace Environmental Exposure Level Guide — Trichlorosilane. Fairfax, VA: AIHA, 1998. Check TERA.org for the latest WEEL information and citation.
Carpenter, C.P. and H.F. Smyth, Jr.: Chemical Burns of the Rabbit Cornea. Am. J. Ophthalmol. 29:1363–1372 (1946).
Dodd, D.E., I.M. Pritts, P.E. Losco, and E.H. Fowler: Nine-Day Inhalation Studies with Dichlorosilane (DCS) and Trichlorosilane (TCS). Export, PA: Bushy Run Research Center, September 1989.
Dow Corning Corporation: A Comparison of Acute Inhalation Toxicity of a Series of Chlorosilanes with Hydrogen Chloride in Rats (Dow Corning Toxicology Report No. 1260). Midland, MI: Dow Corning Corp., September 1987. 18:515–522 (2006).
General Electric Co.: MSDS for GE Product SC3008 Trichlorosilane. Waterford, NY: General Electric Co., April 1994.
Izmerov, N.F., et al.: Toxicometric Parameters of Industrial Toxic Chemical Under Single Exposure. Moscow, USSR: Centre of International Projects, GKNT, 1982. [As cited in Lewis, R.J., Sr.: Sax’s Dangerous Properties of Industrial Materials, 8th edition. New York: Van Nostrand Reinhold, 1992. p. 3361.
Isquith, A.J. and B.J. Miller: Mutagenicity Evaluation of Dow Corning Z–1210 Silane in the Ames Bacterial Assay (Dow Corning Corp. Toxicology Department Report.). Midland, MI: Dow Corning Corp., April 1981.
Jean, P.A., R.H. Gallavan, G.B. Kolesar, W.H. Siddiqui, J.A. Oxley, and R.G. Meeks: Chlorosilane Acute Inhalation Toxicity and Development of an LC50 Prediction Model. Inhalation Toxicol., 18:515-522 (2006)
Nachreiner, D.J. and Dodd, D.E: Acute Inhalation Toxicity Test. Bushy Run Research Center. (1986). (As cited in IUCLID)
National Academies Press: Acute Exposure Guideline Levels for Selected Airborne Chemicals. Volume 11, 2012.
National Research Council: Emergency and Continuous Exposure Guidance Levels for Selected Airborne Contaminants, Vol. 7 — Ammonia, Hydrogen Chloride, Lithium Bromide, and Toluene. Washington, D.C.: National Academy Press, 1987.
Promisloff, R.A., G.S. Lenchner, and A.V. Cichelli: Reactive Airway Dysfunction Syndrome in Three Police Officers following a Roadside Chemical Spill. Chest 98:928–929 (1990).
Smyth, H.F., Jr., C.P. Carpenter and C.S. Well: Range-Finding Toxicity Data, List III. J. Ind. Hyg. Toxicol. 31:60–62 (1949).
Union Carbide Corporation: Rabbit Eye and Skin Injury Testing on Seven Silica Compounds (Report 10–91). Danbury, CT: Union Carbide Corp., August 1986.
Union Carbide Corporation: Data Sheet for Trichlorosilane. Danbury, CT: Union Carbide Corp., February 1979. (From RTECS)
Union Carbide Corporation: Silicon Compounds: Delayed Eye Burns (Report 11–7). Danbury, CT: Union Carbide Corp., August 1994.
U.S. Coast Guard (USCG): Chemical Hazard Response Information System — Manual Guide for Trichlorosilane. Washington, D.C.: U.S. Coast Guard, January 1991.
US Occupational Safety and Health Administration (OSHA), “Limits for Air Contaminants”. Code of Federal Regulations Title 29. Part 1910. Section 1000, Table Z-1-A. 1990