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:
itiatives, this revision provides performance-based guidance rather than traditional prescriptive guidance. 1.78-3 The June 1974 version of Regulatory Guide 1.78 specified a 2-minute exposure to given concentration limits of certain toxic chemicals. The 2-minute exposure criterion was based on the time a control room operator is expected to take to don a respirator and protective clothing. The concentration limits were based on outdated and often unverifiable references. Further, only a limited number of chemicals have the toxicity limits specified in the 1974 guide. The National Institute for Occupational Safety and Health (NIOSH) has published updated toxicity limits for many hazardous chemicals, based on the Immediately Dangerous to Life and Health (IDLH) exposure level concept (Ref. 5). 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. The IDLH exposure limits were developed for respirator selection for a large number of chemicals, including those covered in this regulatory guide. The use of IDLH values as toxicity limits is considered appropriate since it provides an adequate margin of safety as long as control room operators use protective measures within 2 minutes after the detection of hazardous chemicals; they therefore would not be subjected to prolonged exposures at the IDLH concentration levels. Therefore, these limits are included in this revision of Regulatory Guide 1.78. Many of the regulatory positions in the original Regulatory Guides 1.78 and 1.95 are the same or similar. This revision combines these two guides, thereby making the positions applicable to all toxic chemicals, including chlorine, that should be considered in the control room habitability evaluation. Combining the two guides eliminates certain duplication of efforts for licensees in submitting their applications and