Dana M. Arenius
Mathew C. Wright
JLAB-TN-07-075
ODH Risk Assessment, 19 Rooms in Bldg 58
December 19, 2007 RevC
Introduction
This assessment addresses the risk of oxygen deficiency hazard for rooms within Building 58. The assessment is conducted according to the requirements of Appendix 6500-T3, “ODH Risk Assessment”. Three general categories of ODH hazards are identified in the facility. These are sources of nitrogen, helium, and argon gas which can dilute the normal oxygen content with health effects as outlined in Appendix 6500-T3.
The following sections cover the modeling scope and methodology for the cryogen dispersion release, a description of the work space, risk assessment, failure rates of components, and requirements.
Model for Cryogen Dispersion Release
The Model for Cryogen Dispersion Release is based on a ½ inch GN2 supply line with 80 PISG supply pressure. There are also warm gaseous helium and argon sources. Because of the large capacity of the nitrogen dewar, the nitrogen source will be treated as an infinitesupply. The helium and argon is supplied from bottles and / or portable dewars and therefore will be treated as a fixed volume.
Because the nitrogen is considered to be an infinite source, the roomshave been modeled to limit the nitrogen flow and never let the oxygen levels go below 18%. This means that there has to be limiting devices in the supply lines that are outside the room. This also means that there must be an interlock outside the room that will shut of the nitrogen source if the room make-up fresh air supply is not on.
The model for an oxygen deficiency hazard is based on the largest quantityof gaseous nitrogen, helium and argon being available for use. Failure rate estimates (Pi) are based on JLAB listed equipment rates under EH+S Section 6500. Fatality Factors (Fi) are derived from Figure 3, of the EH+S Appendix 6500-T3. The sum of the failure product of the Fi and Pi determined the area classificationin accordance with table 6 of Section 6500 of the EH+S manual.
Description of Work Space
The room floor areasare listed in Table 1. They are all assumed to have a 10 footceiling, except the southeast annex (rooms 147…), second floor tech shop area (rooms 265…) and Room 262. The rooms range from large work spaces to smaller office size rooms. In general, gaseous nitrogen, helium, and argon are located in these rooms.
Gaseous Nitrogen Sources
The gaseous nitrogen ODH source is a3000 gallon dewar. Liquid nitrogen is piped from the dewar to an ambient vaporizer. The gas that leaves the vaporizer is then piped to a header. From the header it is then piped in several different size pipes to several locations including the rooms listed in Table 1. This dewar represents approximately 280,000 standard cubic feet (SCF) of nitrogen gas at 70ºF. If the nitrogen was accidentally released into an unventilated room, for example the oxygen level could reach a very dangerous low level.
Gaseous Helium and Argon Sources
The total gaseous content of helium and argonfrom gas bottles or liquid dewars cannot exceed the release amount allowed within an hour as shown in Table 1, Column 3.
Type of Ventilation
In accordance with Appendix 6500-T3, reliable ventilation may be considered as a relevant factor for this ODH assessment. The only ventilation for these roomscomes from air handing units. These unitsare on 24 hours a day and 7 days a week. It is required to replace the volume of air in the room ata minimum of once an hour. Typically the air is pumped from the air handling units to the rooms through several supply ducts and returned with added fresh make-up air through a central return duct for each room. All air ducts are in the ceiling.
ODH Risk Assessment
The following are a set of events of associated probability and fatality factors that are true only after the previously mentioned engineering controls have been implemented.
Event / Spill RateSCFM / Spill
cf / %O2 / Pi / Fi
Fitting / See table 1 / 280,000 / 18.6 / See note / 0
Power Outage / 0 / 0 / 21 / See note / 0
Operator Error / See table 1 / 280,000 / 18.6 / See note / 0
Valves / See table 1 / 280,000 / 18.6 / See note / 0
Hose / See table 1 / 280,000 / 18.6 / See note / 0
Pi note: The probability factor Pi is assumed to be 0 ≤ Pi ≤ 1 for this ODH analysis. It does not depend on the value of Pi. For all values of probability engineering ventilationinterlock controls will maintain O2 levels >18.6% where the fatality factor Fiwill always be equal to zero. Therefore for all values of Pi.
ODH Classification
Because Φ< 10-7, the ODHclassification is 0for all rooms.
Engineering Controls
The following engineering controls are necessary to provide a safe working environment while retaining an ODH 0 posting.
This analysis requires an interlock between the nitrogen source and the air handling unit. This interlock is to be a failed closed solenoid valve up stream and outside of the room that closes when the air handing unit is not working.
In addition an orifice plate must be used similar as shown in the following sketch and that the orifice sizes are that which are listed in Table 1. This will limit the N2 flow rates which allow the ventilation air to maintain O2 levels > 18.6%.
Table 1
Room / Room / N2 Released / Actual / Required / Ratio of / OrificeNumber / Foot Print / per hour / Air Change / N2 / N2 Supplied / / Bore
SQ FT / SCFH / SCFH / SCFH / N2 Required / (in)
input / input / D*E / input / input / F/J / M*0.43
10A / 1836 / 11806 / 119615 / 240 / 10.6 / .1871
10B / 636
N7 / 2326
ZC / 200
ZD / 534
206 / 560
207 / 752
208 / 673
209 / 1635
15 / 1972 / 2544 / 29736 / 240 / 10.6 / 0.1871
110 / 1659 / 2140 / 26906 / 240 / 8.92 / 0.1742
111 / 133 / 2140 / 18900 / 240 / 8.92 / 0.1742
112 / 592 / 764 / 9601 / 120 / 6.36 / 0.1041
113 / 224 / 289 / 3633 / 240 / 1.2 / 0.0645
114 / 233 / 301 / 3779 / 0 / - / 0
115 / 757.5 / 977 / 347340 / 240 / 4.07 / 0.117
118 / 447 / 577 / 13410 / 240 / 2.40 / 0.0865
127 / 708 / 913 / 285420 / 120 / 7.61 / 0.114
130 / 1267 / 1634 / 82020 / 900 / 1.82 / 0.25
140 / 901 / 1162 / 354000 / 240 / 4.84 / 0.1269
143 / 971 / 1253 / 19083 / 600 / 2.09 / 0.1333
144 / 444.6 / 574 / 70261 / 240 / 2.39 / 0.0912
145 / 622 / 802 / 122759 / 60 / 13.37 / 0.1066
146A / 684 / 882 / 36000 / 180 / 4.9 / 0.1127
146B / 444 / 573 / 0 / 240 / 2.39 / 0
147 / n/a / 5449 / 7260 / 0 / - / 0
148
149
CG3
P
RA3
153 / 814.5 / 1051 / 46800 / 420 / 2.5 / 0.1204
262 / 811 / 1046 / 18000 / 300 / 3.49 / 0.1204
263 / 340 / 439 / 540 / 0 / - / 0
264 / 340 / 439 / 4560 / 360 / 1.22 / 0.0796
266 / 182 / 235 / 21600 / 240 / 1.83 / 0.0731
265 / 377 / 573 / 36600
267 / 308 / 120 / 4.78 / 0.0753
X / 540
281 / 229 / 295 / 63840 / 60 / 4.92 / 0.0654
Basement / 4980 / 6424 / 60000 / 120 / 53.54 / 0
Notes: Where the orifice bore has a value of 0.0000 the orifice must remain blank until such time when the specific room ventilation can be increased to at least one air change per hour. Until such time, no N2 source will be allowed to enter the room.