TITLE:

ES&H Manual

 

DOCUMENT ID:

6540 Appendix T4

Oxygen Deficiency Hazard (ODH)

Risk Assessment

 

 

1.0            Purpose

An Oxygen Deficiency Hazard (ODH) Risk Assessment is performed when gas is proposed, switched, or discovered in a process or an area AND either:

·       the ODH Safety Review results in an O2 percentage below 18

·       the ODH Safety Reviewer requests a Risk Assessment when the resulting O2 percentage is between 18-19.5

·       the ODH in question involves a complex system

·       prior experience has demonstrated that a risk assessment is necessary

·       as requested in accordance with ES&H Manual Chapter 3210 Work Planning, Control, and Authorization Process.

If the potential ODH is located outdoors, consult another ODH Analysis Authority or SME for the area to determine if a Risk Assessment is required. The format for the Risk Assessment shall follow the format detailed here; however, special methodologies will likely be necessary to cover the unique considerations for outdoor scenarios.

Relevant factors for all ODH Risk Assessments include, but are not limited to:

·         Volume of the area

·         Potential volume of the gas

·         Work to be performed in the area

·         Effects produced by reduced atmospheric oxygen

·         Likelihood of equipment failure

·         Likelihood of human error

·         Reliability of safety and ventilation equipment

·         Engineering controls currently in place and required to maintain ODH classification

·         Required administrative controls

·         Existing ODH sources or installations

·         Ease of egress

·         Passive vent areas

·         Final ODH Classification based on analysis

 

2.0            Scope

This appendix provides instructions on how to complete an ODH Risk Assessment so an accurate determination of risk can be made, ODH Classifications can be identified and appropriate mitigation can be implemented.

3.0            Responsibilities

NOTE:           Management authority may be delegated to a task qualified Jefferson Lab employee at the discretion of the responsible manager.

3.1              Division Safety Officers

·         Ensure an ODH Safety Review/Risk Assessment has been performed and is current for any ODH area where individuals under your authority are assigned. IT IS IMPORTANT TO CONSIDER AND MITIGATE AN ODH EARLY IN THE DESIGN/FABRICATION PROCESS.

·         Review ODH Risk Assessment(s) and associated documentation every 3 years if ODH is present or when conditions change.

 

3.2              ODH Analysis Authority

·         Conduct and/or review ODH Risk Assessments when required or requested in accordance with this Appendix.

·         Upon request, perform a review of an ODH Risk Assessment and associated documentation every 3 years if an ODH is present.

·         Qualifications include:

o   Demonstrated ability to analyze and mitigate oxygen deficiency hazards within laboratory user systems. 

o   Maintain appropriate training SAF103 Oxygen Deficiency Hazard  

o   Technical proficiencies and knowledge of: 

§  ODH evaluations, calculations, design/implementation of control measures 

§  Common compressed and liquefied gases, mixed gas properties 

§  ODH propagation calculations 

§  Pressurized gas mechanical systems with their associated failure modes analysis 

o   One of the following:

§  Completion of an engineering or physics degree, requiring four or more years of full time study, plus a minimum of five years of experience relating to the technical requirements listed above.

§  Professional Engineering registration, recognized by the local jurisdiction, plus experience in systems relating to ODH classification, mitigation, evaluation, and their properties.

3.3              ODH Safety Reviewer

·         Submit a request for an ODH Risk Assessment as appropriate.

·         Review the ODH Risk Assessment conclusions (Class 0, 1 or 2 designation and identification of mitigation measures) and approve risk assessment if acceptable.  

·         Distribute/File final approved ODH Risk Assessment to affected area, Document Owner and ESH&Q Document Control.

·         Requests/Informs Engineering Division Safety Systems Group of ODH system requirements.

·         Verify that ODH equipment safeguards, inventory requirements, posting, and labeling are in-place prior to introduction of the ODH.

·         Coordinate with DSOs to ensure ODH Risk Assessments are reviewed every 3 years or when conditions change.

3.4              Engineering Division

·         Safety Systems Group and Cryogenic Operations: Install, maintain and calibrate area oxygen monitoring systems associated with accelerator enclosures (e.g. CEBAF, LERF, UITF) under their purview.

·         Engineering Division Manager or the Cryogenic Department Head: Approve ODH Risk Assessments.

 

3.5              Physics and Accelerator Divisions

·         Install, maintain and calibrate area oxygen monitoring systems under their purview.

 

3.6              Facilities Management and Logistics

·         Provide room measurements upon request.

·         Provide ventilation capacities upon request.

·         Provide and maintain building ventilation systems.

·         Install, maintain and calibrate area oxygen monitoring systems under their purview.

4.0            Expectations

An ODH Analysis Authority may delegate the authorship of an ODH Risk Assessment to an individual who does not meet the qualifications of an ODH Analysis Authority. In all cases, the ODH Analysis Authority maintains responsibility for that ODH Risk Assessment and must approve the work product as the Primary ODH Analysis Authority. 

 

An ODH Risk Assessment is a quantitative assessment of the increased risk of fatality from exposure to reduced atmospheric oxygen and shall be conducted for all operations which are physically capable of exposing individuals to an atmosphere below 18 % O2, or as requested by the ODH Safety Reviewer. This assessment shall assign an ODH Classification (See Table 1) to each area with potential risk as well as specify any precautionary requirements or mitigation measures. The classification of an area can change depending on the operations being performed. If conditions and/or activities change in ways that significantly increase the risk, the associated quantitative assessment must be accordingly revised, reviewed and approved.

Table 1. ODH Classification

ODH Class

# of worker-hours* during which a fatality is expected

Φ: the ODH fatality rate (per hour)

0

Greater than 10 million

<10-7

1

from 100,000 hours to 10 million

≥10-7 but < 10-5

2

from 1,000 to 100,000

≥10-5 but < 10-3

3

from 10 to 1,000

≥10-3 but < 10-1

4

less than 10

≥10-1

*2000 worker-hours equals one year.

 

4.1              ODH Risk Assessment Format

Each ODH Risk Assessment shall follow the outlined format below including the expectations listed in the bullets. The ODH Analysis Authority is encouraged to use previous ODH Risk Assessments for informational purposes; however, the format below must be used in the new ODH Risk Assessment. Examples of approved ODH Risk Assessments can be found in the ODH Risk Assessments and Safety Reviews folder on the ESH&Q Work Control Documents pages.

 

4.1.1        Cover Sheet

·         Date

·         Division of ODH Analysis Authority

·         Location of ODH

·         Primary ODH Analysis Authority

·         Approvals

o   At a minimum, all ODH Risk Assessments must be approved by all of the following:

§  the Primary ODH Analysis Authority

§  another ODH Analysis Authority

§  the Engineering Division Manager or the Cryogenic Department Head.

o   The ODH Risk Assessment shall be submitted to the ODH Safety Reviewer for verification and approval.

4.1.2        Introduction

·         General information on location, equipment and ODH sources

·         Include an expected date when the ODH source will be introduced

4.1.3        Description of Work Space

·         Details of area including volume, doorways, penetrations, venting, etc.

·         Include figures with elevation views as appropriate

·         Describe ventilation systems and capacities

4.1.4        ODH Sources

·         Identify all potential ODH sources (helium, nitrogen, or others)

·         Include total inventory and continuous flow rates as appropriate

4.1.5        Identification of ODH Scenarios

·         Include all possible cases for ODH determination (instantaneous venting of entire ODH source, continuous flow into work space, etc.)

·         Consider gas mixing and stratification in defining cases

·         Clearly identify whether ventilation is included in each case

4.1.6        Risk Assessment Methodology

·         Follow the guidelines presented in Section 4.2 Estimation of ODH Fatality Rate. Using these guidelines, the ODH Analysis Authority shall determine the expected rate of an event occurring (Pi per hour), the expected oxygen concentration (%O2) and the associated fatality factor (Fi) for each event. These values are used to determine the ODH fatality rate (f per hour) for each identified ODH scenario.

·         The ODH Analysis Authority may use an alternative approach provided that approach is an accepted by another ODH Analysis Authority, the Engineering Division Manager, or Cryogenic Department Head.

4.1.7        ODH Classification

·         Use Table 1 ODH Classification and the calculated ODH fatality rate (f per hour) to clearly identify Class 0, 1, or 2 for each identified ODH scenario. Class 3 and 4 are included in the table; however, they are considered unacceptable as an ODH Risk Assessment result. Further mitigations to lower the classification would be necessary before the risks are considered acceptable.

4.1.8        Engineering and Administrative Controls

·         Identify the engineering controls necessary to provide a safe working environment and to retain ODH Classification (lintels, ventilation, penetration sealing, etc.)

·         Identify administrative controls such as ODH monitoring, alarms and signage

 

After final approval, the ODH Safety Reviewer shall distribute/file the Risk Assessment and associated documentation to the affected area, Document Owner and ESH&Q Document Control. The ODH Safety Reviewer shall verify ODH equipment safeguards, inventory requirements, posting, and labeling, are in-place prior to introduction of the ODH.

 

The ODH Risk Assessment shall be reviewed by an ODH Analysis Authority (typically the original author if available) every 3 years provided the ODH is present.

4.2              Estimation of ODH Fatality Rate

The goal of ODH risk assessment is to estimate the increase in the rate at which fatalities will occur as a result of exposure to reduced-oxygen atmospheres.

 

Since the level of risk is tied to the nature of the operation, the excess fatality rate shall be determined on an operation-by-operation basis. For a given operation several events may cause an oxygen deficiency. Each event has an expected rate of occurrence and each occurrence has an expected probability of causing a fatality. The ODH fatality rate is defined as:

 

 

where:

f = the ODH fatality rate (per hour)

Pi = the expected rate of the ith type of event, (per hour)

Fi = the fatality factor for the ith type event.

 

The summation shall be taken over all types of events which may cause oxygen deficiency and result in fatality. This summation must be made for each identified ODH scenario. Methods for determining the expected rate of an event occurring (Pi per hour) and the fatality factor (Fi) for an event are discussed below:

 

4.3              Estimation of event rates, Pi

When possible, the value of Pi shall be determined by operating experience at Jefferson Lab; otherwise, data from similar systems elsewhere or other relevant values shall be used. Estimates of “spontaneous” equipment failure rates are given in Tables 2 and 3. Human error rate estimates are presented in Tables 4 and 5. Information is presented either as a time rate (x/hr) or per demand rate (x/D).

 

Table 2: Equipment Failure Rate Estimates *

System

Failure Mode

Failure Rate

Compressor

(Two-stage Mycom)

Leak

Component rupture

5 x 10-6/hr

3 x 10-7/hr

Dewar

Loss of vacuum

1 x 10-6/hr

Electrical Power Failure

(unplanned)

Time Rate

Demand Rate

Time Off

1 x 10-4/hr

3 x 10-4/D

1 hr

Fluid Line

(Cryogenic)

Leak

Rupture

5 x 10-7/hr

2 x 10-8/hr

Cryogenic Magnet

(Powered, unmanned)

Rupture

2 x 10-7/hr

Cryogenic Magnet

(Not powered, manned)

Rupture

2 x 10-8/hr

Header Piping Assembly

Rupture

1 x 10-8/hr

U-Tube Change

(Cryogen Release)

Small Event

Large Event

3 x 10-2/D

1 x 10-3/D

*Median estimates excerpted from FESHM-4240 Technical Appendix, Rev 11/2016

 

Table 3:  NRC and Industry Equipment Failure Rate Estimates **

 

Equipment

Failure Mode

Median

Failure Rate

 

Batteries

Power supplies

No output

3 x 10-6/hr

 

Circuit breakers

Failure to operate

Premature transfer

1 x 10-3/D

1 x 10-6/hr

 

Diesel (complete plant)

(emergency loads)

Diesel (engine only)

Failure to start

Failure to run

Failure to run

3 x 10-2/D

3 x 10-3/hr

3 x 10-4/hr

 

Electric Motors

Failure to start

Failure to run

Failure to run-extreme environment

3 x 10-4/D

1 x 10-5/hr

1 x 10-3/hr

 

Fans

(fans, motor & starter)

Failure to run

Failure to stat on demand

9 x 10-6/hr

***

 

Fuses

Premature, open

Failure to open

1 x 10-6/hr

1 x 10-5/D

 

Flanges with Reinforced & Preformed Gaskets

Leak, 10 mm2 opening

Rupture

4 x 10-7/hr

1 x 10-9/hr

 

Flanges with Packing or Soft Gaskets

Leak, 10 mm2 opening

Packing blowout

Rupture

4 x 10-7/hr

3 x 10-8/hr

1 x 10-9/hr

 

Instrumentation

(amplification, annunciators, transducers, calibration, combination)

Failure to operate

Shifts

1 x 10-6/hr

3 x 10-5/hr

 

Motorized Louver

Failure in continuous operation

Failure to open on demand

3 x 10-7/hr

***

 

Piping

Small leak, 10 mm2

Pipes >2”, large leak, 1000 mm2

Rupture

1 x 10-9/meter-hr

1 x 10-10/meter-hr

1 x 10-11/meter-hr

 

Pipes Welds

 D = diameter

 t = wall thickness

Small leak, 10 mm2

Pipes >2”, large leak, 1000 mm2

Rupture

2 x 10-11*(D/t)/hr

2 x 10-12*(D/t)/hr

6 x 10-13*(D/t)/hr

 

 

Pumps

Failure to start

Failure to run-normal

Failure to run-extreme environment

1 x 10-3/D

3 x 10-5/hr

1 x 10-3/hr

 

Relays

Failure to energize

Failure-no contact to close

Short Across NO/NC contact

Open NC contact

1 x 10-4/D

3 x 10-7/hr

1 x 10-8/hr

1 x 10-7/hr

 

Solid State Devices:

Hi Power Application

Fails to function

Shorts

3 x 10-6/hr

1 x 10-6/hr

 

Solid State Devices:

Low Power Application

Fails to function

Shorts

1 x 10-6/hr

1 x 10-7/hr

 

Switches

Limit : Failure to operate

Torque: Failure to operate

Pressure: Failure to operate

Manual: Failure to transfer

Contacts short

3 x 10-4/D

1 x 10-4/D

1 x 10-4/D

1 x 10-5/D

1 x 10-8/hr

 

Transformers

Open CKT

Short

1 x 10-6/hr

1 x 10-6/hr

 

Valves, Motor operated

Failure to operate (plug)

Failure to remain open

External leak

Rupture

1 x 10-3/D

1 x 10-4/D

1 x 10-8/hr

5 x 10-10/hr

 

Valves, Solenoid operated

Failure to operate

1 x 10-3/D

 

Valves, Air operated

Failure to operate (plug)

Failure to remain open

External leak

Rupture

3 x 10-4/D

1 x 10-4/D

1 x 10-8/hr

5 x 10-10/hr

 

Valves, Check

Failure to open

Reverse Leak

External Leak

Rupture

1 x 10-4/D

3 x 10-7/hr

1 x 10-8/hr

5 x 10-10/hr

 

Valves: Orifice, Flow Meters (test)

Rupture

1 x 10-8/hr

 

Valves, Manual

Failure to remain open (plug)

External leak

Rupture

1 x 10-4/D

1 x 10-8/hr

5 x 10-10/hr

 

Valves, Relief

Failure to open per demand

Premature open per hour

1 x 10-5/D

1 x 10-5/D

 

Vessels, Pressure

Small leak, 10 mm2

Disruptive failure

8 x 10-8/hr

5 x 10-9/hr

 

**    Estimates excerpted from FESHM-4240, Technical Appendix, Rev 11/2016

***  If needed, reference FESHM-4240, Technical Appendix (6.4)

 

Table 4:  Human Error Rate Estimates

Estimate

error rate

per demand

Activity

10-3

Selection of a switch (or pair of switches) dissimilar in shape or location to the desired switch, assuming no decision error.  For example, operator actuates large handled switch rather than small switch.

3 x 10-3

General human error of commission, e.g., misreading label and therefore selecting wrong switch.

10-2

General human error of omission where there is no display in the control room of the status of the item omitted, e.g., failure to return manually operated test valve to proper configuration after maintenance.

3 x 10-3

Errors of omission, where the items being omitted are embedded in a procedure rather than at the end of a procedure as above.

1/x

Given that an operator is reaching for an incorrect switch (or pair of switches), he/s

he selects a particular similar appearing switch, where x = the number of incorrect switches adjacent to the desired switch.  The 1/x applies up to 5 or 6 items.  After that point the error rate would be lower because the operator would take more time to search.  With up to 5 or 6 items he/she doesn’t expect to be wrong and, therefore, is more likely to do less deliberate searching.

10-1

Monitor or inspector fails to recognize initial error by operator.  Note: With continuing feedback of the error on the annunciator panel, this high error rate would not apply.

10-1

Personnel on different work shifts fail to check condition of hardware unless required by check or written directive.

5 x 10-1

Monitor fails to detect undesired position of valves, etc., during general walk-around inspections, assuming no check list is used.

0.2-0.3

General error rate given very high stress levels where dangerous activities are occurring rapidly.

2(n-1)x

Given severe time stress, as in trying to compensate for an error made in an emergency situation, the initial rate, x, for an activity doubles for each attempt, n, after a previous incorrect attempt, until the limiting condition of an error rate of 1.0 is reached or until time runs out. This limiting condition corresponds to an individual’s becoming completely disorganized or ineffective.

 

Table 5:  Human Error Rate as a Function of Response Time

Maximum Estimated

Error Rate per Demand

Response Time (sec)

Skill-based Task

Rule-based Task

Knowledge-based Task

10-4

37

600

18,000

10-3

26

300

10,000

10-2

16

130

4,900

10-1

8.7

42

1,800

5 x 10-1

4.0

10

550

1)           Skill-based Task – An individual initiates a single-step learned response upon receipt of an unambiguous sensor cue. (Example: A lone worker initiates escape upon hearing an oxygen deficiency alarm.)

2)           Rule-based Task – An individual or small group of individuals diagnoses and initiates corrective actions for a simple problem given limited or ambiguous input. (Example: Several workers decide whether or not to escape given that one of them passes out but no oxygen deficiency alarms sound.)

3)           Knowledge-based Task – A group of individuals diagnoses and initiates corrective actions for a novel and/or complex problem.

4.4              Estimation of O2 Concentration

The ODH Analysis Authority shall calculate the %O2 for each identified ODH Scenario considering mixing and stratification. Flow rates and oxygen concentration over time shall be calculated as appropriate. For valuable methodologies used in calculating %O2, consult previous ODH Risk Assessments and/or the Fermilab guidance in FESHM 4240TA: Oxygen Deficiency Hazards (ODH) Nov. 2016 provided below. For information on gas discharge rates through relief devices or punctures/leaks, see Reference 4, Jia, L.X. and Wang, L. 2002 Equations for Gas Releasing Process from Pressurized Vessels in ODH Evaluation.

 

(excerpted from FESHM 4240TA: Oxygen Deficiency Hazards (ODH) Nov. 2016)

The oxygen concentration in a confined volume during and after a release of an inert gas may be approximated with the following equations. Five different cases are presented:

 

Case A: During release, with perfect mixing - Ventilation fan(s) blowing into the confined volume

Case B:   During release, with perfect mixing - Ventilation fan(s) drawing from the confined volume with the ventilation rate greater than the spill rate

Case C:   During release, with perfect mixing - Ventilation fan(s) drawing from the confined volume with the ventilation rate less than or equal to the spill rate

Case D: After release, with perfect mixing

Case E:   Stratification of inerting gases

The equation and its solution are given which are based on an oxygen mass balance for the confined volume. The following definitions and assumptions are common for each case:

Definition of terms:

C = oxygen concentration

Cr = oxygen concentration during the release

Ce = oxygen concentration after the release has ended

Q = ventilation rate of fan(s), (cfm or m3/s)

R = spill rate into confined volume, (scfm or m3/s)

t = time, (minutes or seconds) beginning of release is at t=0

te = time when release has ended, (minutes or seconds)

V = confined volume, (ft3 or m3)

Assumptions:

·         For Cases A through D, complete and instantaneous mixing takes place in the confined volume. This is only a good assumption where gases have similar densities and/or mixing is "vigorous."

·         Q, R, and V remain constant.

·         Pressure in the confined volume remains constant and very near atmospheric pressure through the use of louvers or natural leakage.

·         Gas entering from outside the confined volume is air with an oxygen concentration of 0.21 (21%).

Case A: During release - Ventilation fan(s) blowing outside air into the confined volume.

Differential equation for the oxygen mass balance

                                                               (1)                                                                                        

Solution with the boundary condition of C=0.21 at t=0

                                                               (2)                                               

Case B: During release - Ventilation fans(s) drawing contaminated atmosphere from the confined volume with the ventilation rate greater than the spill rate (Q>R).

Differential equation for the oxygen mass balance

                                                               (3)                                                                                                     

Solution with the boundary condition of C=0.21 at t=0

                                                               (4)                                                      

Case C: During release - Ventilation fans(s) drawing contaminated atmosphere from the confined volume with the ventilation rate less than or equal to the spill rate (Q ≤ R).

Differential equation for the oxygen mass balance

 

                                                               (5)                                               

Solution with the boundary condition of C = 0.21 at t = 0

                                                               (6)                                               

Case D: After release - The oxygen concentration in the confined volume after the release has ended, Ce(t), can be approximated by one equation.

 

Differential equation for the oxygen mass balance

                                                               (7)                                                  

Solution with the boundary condition of C = Cr (te) at t = te

                                                               (8)                                               

where (t - te) is the time duration since the release ended.

 

Case E: Stratification of gases - The effects of stratification must be considered. The oxygen concentration can vary depending on distance from the release, elevation, gas density, ventilation, time and other factors. In most cases simple, conservative assumptions regarding mixing are more suitable than attempting a precise evaluation of mixing. For large enclosures it may be reasonable to assume complete mixing in a portion of the volume. Stratification should not be used to reduce the risk.

 

4.5              Fatality Factor, Fi

The value of Fi is the probability that a person will die if the ith event occurs. This value depends on the oxygen concentration, the duration of exposure, and the difficulty of escape. For convenience of calculation, a relationship between the value of Fi and the lowest attainable oxygen concentration is defined (Figure 1). (The lowest concentration is used rather than an average since the minimum value is conservative and not enough is understood to allow the definition of an averaging period.)

 

Once % O2 has been identified for each ODH Scenario, the ODH Analysis Authority shall identify the associated Fatality Factor (Fi) using Figure 1.

Figure 1:  Fatality Factor (Fi) vs lowest attainable 02 concentration resulting from a given event

If the lowest oxygen concentration is greater than 18%, then the value of Fi is zero. That is, all exposures above 18% are defined to not contribute to fatality. It is assumed that all exposures to 18% oxygen or lower do contribute to fatality and the value of Fi is designed to reflect this dependence.

 

If the lowest attainable oxygen concentration is 18%, then the value of Fi is 10-7. This value would cause f to be 10-7 per hour if the expected rate of occurrence of the event were one per hour. At decreasing concentrations, the value of Fi should increase until, at some point, the probability of dying becomes unity. That point was selected to be 8.8% oxygen, the concentration at which one minute of consciousness is expected.

 

5.0            References

·        FESHM 4240: Oxygen Deficiency Hazards (ODH), Fermilab ES&H Manual, November 2016.

·        Jefferson Lab ODHRAP [formerly ES&H Manual Chapter 6500 Appendix T3 Oxygen Deficiency Hazard (ODH) Risk Assessment].

·        Reactor Safety Study:  An Assessment of Accident Risks in US Commercial Power Plants Appendix 3&4: Failure Data, US Nuclear Regulatory Commission; US Department of Commerce-National Technical Information Service, PB-248 204, October 1975.

·        Jia, LX and Wang, L 2002, ‘Equations for Gas Releasing Process from Pressurized Vessels in ODH Evaluation’, in S Breon, et al. (eds.), CP613, Advances in Cryogenic Engineering: Proceedings of the Engineering Conference, Vol.47, 2002 American Institute of Physics, pp. 1792-8.

6.0            Revision Summary

Revision 0.0 – 10/31/17 – Initial content

 

 

 

ISSUING AUTHORITY

TECHNICAL POINT-OF-CONTACT

APPROVAL DATE

REVIEW DATE

REV.

 

 

ESH&Q Division

Jennifer Williams

11/06/17

11/06/20

0.0

 

This document is controlled as an on line file.  It may be printed but the print copy is not a controlled document.  It is the user’s responsibility to ensure that the document is the same revision as the current on line file.  This copy was printed on 11/7/2017.