Document: NRC Regulatory Guide
Document ID: ceaeb6d7-d85a-46d3-a1b6-70059a498965
Document Type: regulatory_guide
Title: 12/2001 (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0131/ML013100014.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.78
CFR Part: 
CFR Title: 

Content:
g a detailed evaluation of control room habitability during a hazardous chemical release using this guidance, the metric to be used for each chemical is the maximum concentration (toxicity limit) that can be tolerated without physical incapacitation of a control room operator. In deriving the toxicity level in the control room, the detailed calculations should take into account several factors: accident type, release characterization (e.g., release rate, duration), atmospheric dispersion characteristics including prevailing meteorological conditions at the site, and the air exchange rate of the control room. Guidance pertaining to the detailed calculations is provided below. Table 2 of this guide lists the chemical and control room data for an evaluation of control room habitability. 3.1 Toxicity Limits Table 1 gives the toxicity limits (in ppm by volume and mg/m3) for the chemicals listed; a more complete list of chemicals and their toxicity limits is provided in Reference 5. These limits are based on the immediately dangerous to life and health (IDLH) exposure level concept (Ref. 7) formulated by the National Institute for Occupational Safety and Health (NIOSH). The IDLH value or limit, based on a 30-minute exposure level, is defined as one that is likely to cause death or immediate or delayed permanent adverse health effects if no protection is afforded within 30 minutes. For each chemical considered, the IDLH limit can be tolerated for 2 minutes without physical incapacitation (for example, severe coughing, eye burn, or severe skin irritation) of an average human. Thus, a 2-minute exposure to the IDLH limits provides an adequate margin of safety in protecting control room operators, and these limits are recommended (Ref. 5). It is expected that a control room operator will take protective measures within 2 minutes (adequate 1.78-7 time to don a respirator and protective clothing) after the detection and, therefore, will not be subjected to prolonged exposure at