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NOTE: This document is provided for historical purposes only.
The authors ask you:
Fatalities associated with entry into confined-space manure storage facilities occur each year. The fatalities are due to asphyxiation or poisoning by exposure to high concentrations of hydrogen sulphide, methane, and carbon dioxide. Forced ventilation has been shown to be an effective way to reduce concentrations of these gases to levels that are safe for human entry into these facilities. However, research studies on safety ventilation in confined-space manure storage facilities are limited. Meanwhile, safety specialists, waste management engineers, designers, and distributors of manure storage facilities cite the need for engineering standards to properly design the ventilation systems. This research used validated computational fluid dynamics (CFD) modelling protocols to identify effective ventilation strategies to reduce hazardous atmospheres in these facilities. CFD simulation results will be incorporated into developing a safety standard for ventilation of confined-space manure storage facilities before entering. This poster presents the five key steps for the development of the standard.
Fatalities associated with on-farm confined-space manure storage facilities have frequently occurred when a victim enters an unventilated storage to make repairs or perform maintenance without wearing necessary personal protective equipment (PPE). Beaver and Field (2007) summarized documented fatalities in livestock manure storage and handling facilities from 1975 to 2004. One result from this analysis of 77 fatalities cases showed an increasing trend in the death rate per year between 1974 and 2004: 1.6 from 1975 through 1984; 2.7 from 1985 through 1994; 3.5 from 1995 through 2004. The Occupational Safety and Health Administration (OSHA, 2002) has developed confined-space regulations documented in the 29 Code of Federal Regulations (CFR) Part 1910.146. These regulations are summarized in Permit-Required Confined Spaces and require that the internal atmosphere within a confined space be tested for oxygen levels, flammable gases and vapors, and potential noxious contaminants prior to human entry. According to OSHA standards, an employee may not enter a confined space until forced air ventilation has eliminated any existing hazardous atmospheres. However, there is no ventilation standard for safe entry into on-farm confined-space manure pits
Step 1: Measure contaminant gas concentration reduction during forced ventilation of confined-space manure pits (completed)
Figure 1. Geometry of the manure tank for conducting measurements
Figure 2. Typical gas concentration reduction curve during ventilation (H2S)
Step 2: Develop computational fluid dynamics (CFD) modelling protocols for simulation of gas concentration reduction in confined-space manure pits (completed)
Figure 3. Schematic of confined-space manure pit geometry and ventilation scheme for performing CFD simulations (solid cover)
Step 3: Validate/verify the simulated gas concentration reduction curves (completed)
(a) Solid cover
(b) Fully slotted cover
(c) Partially slotted cover
Figure 4. Simulated vs. Measured evacuation times of hydrogen sulphide for three cover types
Table 1. Decision criteria statistics for the CFD simulations for three cover types
| Correlation coefficient | Regression slope | Regression intercept | |
|---|---|---|---|
| Statistical criteria1 | > 0.9 | 0.75 ~ 1.25 | ≤ 25% measured value 2 |
| Solid cover | 0.93 | 1.05 | 1.77 |
| Fully slotted cover | 0.97 | 0.78 | 13.6 |
| Partially slotted cover | 0.81 | 0.77 | 2.31 |
1 Based on the Standard Guide for Statistical Evaluation of Indoor Air Quality
Model (ASTM, D5157-97).
2The mean measured values (TPEL) were 41 s for the solid cover, 87 s for the
fully slotted cover, and 43 s for the partially slotted cover; therefore, 25%
of the mean measured values were 11 s, 22 s, and 11 s for the solid, fully slotted,
and partially slotted cover types.
Step 4: Simulations of gas concentration reduction during ventilation for a wide range (over 150 combinations of size, shape, and ventilation schemes) of confined-space manure storages* with solid (rectangular/circular footprint), totally slotted (rectangular footprint), and partially slotted (rectangular footprint) cover types. (On-going research)
Figure 5. Zones with H2S concentrations < 10 ppm at ventilation times of 60 s, 90 s, 100 s, and 120 s in a confined-space manure pit with a solid cover.
Step 5: Develop standard
The findings and conclusions in this poster are those of the author(s) and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of these Web sites.
