Yoked Corp. can model and prepare reports acceptable to regulating authorities to demonstrate personnel safety.
Studies of Chemical Spill Toxicity & Asphyxiation Concentration Estimating for Habitability
1. Cryogenic Gas Spills
U.S NRC Regulatory Guide 1.78 requires the evaluation of the effects, if any, on the habitability of the main control room (MCR) due to a spill or release of chemicals. This evaluation can be performed using the ALOHA computer code. http://www.hss.doe.gov/nuclearsafety/qa/sqa/central_registry/ALOHA/aloha.htm
The Environmental Protection Agency, the National Oceanic and Atmospheric Administration (NOAA) and the National Safety Council have developed this software for modeling chemical spills.
OSHA sets enforceable permissible exposure limits (PELs) to protect workers against the health effects of exposure to hazardous substances. PELs are regulatory limits on the amount or concentration of a substance in the air. OSHA PELs are based on an 8-hour time weighted average (TWA) exposure within a 40 hour work week.
A large spill of cryogenically stored gases evaporates and dissipates rapidly. The potential effects on an operator in the main control room (MCR) in terms of having a toxic or asphyxiating effect are not the long term exposure effects considered by OSHA. The change in air quality at the MCR air intake due to a gas spill or release will be of minutes in duration, not hours. Therefore, the OSHA PEL does not apply.
The consequence of the air quality change should be evaluated against the National Institute of Occupational Safety and Health (NIOSH) contaminant exposure limits. NIOSH defines recommended exposure limits (REL), short term exposure limits (STEL) and the level considered immediately dangerous to life and health (IDLH). REL refers to long term exposure and is in the same category as OSHA PEL. Exposure to NIOSH REL is permitted for 10 hours/day in a 40 hour workweek.
NIOSH STEL is the exposure limit that is appropriate for confirming MCR habitability. Because the MCR has a limited exchange of outside air, a high short term outside air contaminant concentration at the air intake will result in a diluted, lower concentration inside the MCR. The IDLH is the concentration for which 30 minutes of exposure is likely to cause death or immediate or delayed permanent adverse health effects. Reg. Guide 1.78 permits MCR operators to be exposed to IDLH levels of contaminants for two minutes. Usually, the calculations predict the air quality inside the MCR never to get as bad as the STEL.
ALOHA calculates the concentration of a chemical after a spill as a function of time at a given distance from the spill. The program requires manual inputs of many parameters, including the site location.
2. Liquid Chemical Spills
Each chemical is to be separately evaluated. Some are potential hazards due to toxicity, some as carcinogens and some due to flammability or explosions. Some chemicals at a power plant site are benign and pose no hazard risk.
Chemicals likely to be on a Plant Site to be evaluated are:
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Hydrazine
Carbohydrazide Ammonium Hydroxide Morpholine 3-Methoxy propylamine (MPA) Ethanolamine (EPA) Ammonium Chloride Quaternary Amine Sodium Hypochlorite Stabilized Bromine Sodium Bromide Sodium Hydroxide |
Sulfuric Acid
Boric Acid Zinc Acetate Lithium Hydroxide Sodium Molybdate Sodium Tolytriazole Ethylene Glycol Propylene Glycol Sodium Hypochlorite Sodium Hydroxide Hydrogen Peroxide |
