#### § 50-204.50 Gases, vapors, fumes, dusts, and mists.

(a)

(1) Exposures by inhalation, ingestion, skin absorption, or contact to any material or substance

(i) at a concentration above those specified in the “Threshold Limit Values of Airborne Contaminants for 1968” of the American Conference of Governmental Industrial Hygienists, except for the ANSI Standards listed in Table I of this section and except for the values of mineral dusts listed in Table II of this section, and

(ii) concentrations above those specified in Tables I and II of this section, shall be avoided, or protective equipment shall be provided and used.

(2) The requirements of this section do not apply to exposures to airborne asbestos dust. Exposures of employees to airborne asbestos dust shall be subject to the requirements of [29 CFR 1910.93a](/on/2024-09-20/title-29/section-1910.93a).

(b) To achieve compliance with [paragraph (a)](/on/2024-09-20/title-41/section-50-204.50#p-50-204.50(a)) of this section, feasible administrative or engineering controls must first be determined and implemented in all cases. In cases where protective equipment in addition to other measures is used as the method of protecting the employee, such protection must be approved for each specific application by a competent industrial hygienist or other technically qualified source.

Table II—Mineral Dusts

| Substance | Mppcfe | Mg/M3 |
| --- | --- | --- |
| Silica: | | |
| Crystalline: | | |
| Quartz (respirable) | 250f | 10mg/M3m |
| | %SiO2 = 5 | %SiO2 = 2 |
| Quartz (total dust) | | 30mg/M3 |
| | | %SiO2 = 2 |
| Cristobalite: Use 1/2 the value calculated from the count or mass formulae for quartz. | | |
| Tridymite: Use 1/2 the value calculated from the formulae for quartz. | | |
| Amorphous, including natural diatomaceous earth | 20 | 80mg/M3 |
| | | %SiO2 |
| Silicates (less than 1% crystalline silica): | | |
| Mica | 20 | |
| Soapstone | 20 | |
| Talc | 20 | |
| Portland cement | 50 | |
| Graphite (natural) | 15 | |
| Coat dust (respirable fraction less than 5% SiO2) | | 2.4mg/M3 |
| | | or |
| For more than 5% SiO2 | | 10mg/M3 |
| | | %SiO2 = 2 |
| Inert or Nuisance Dust: | | |
| Respirable fraction | 1 | 5mg/M3 |
| Total dust | 505 | 15mg/M3 |
| | | |
| --- | --- | --- |
| **Note:** Conversion factors— | | |
| mppcf × 35.3 = million particles per cubic meter | | |
| = particles per c.c. | | |
| e Millions of particles per cubic foot of air, based on impinger samples counted by light-field technics. | | |
| f The percentage of crystalline silica in the formula is the amount determined from air-borne samples, except in those instances in which other methods have been shown to be applicable. | | |
| j As determined by the membrane filter method at 430 × phase contrast magnification. | | |
| m Both concentration and percent quartz for the application of this limit are to be determined from the fraction passing a size-selector with the following characteristics: | | |

| Aerodynamic diameter (unit density sphere) | Percent passing selector |
| --- | --- |
| 2 | 90 |
| 2.5 | 75 |
| 3.5 | 50 |
| 5.0 | 25 |
| 10 | 0 |
| | |
| --- | --- |
| The measurements under this note refer to the use of an AEC instrument. If the respirable fraction of coal dust is determined with a MRE the figure corresponding to that of 2.4 Mg/M3 in the table for coal dust is 4.5 Mg/M3 | |

[[36 FR 23217](https://www.federalregister.gov/citation/36-FR-23217), Dec. 7, 1971]