ODH Risk Assessment
underground gallery B887-EHN1
On behalf the working group EN - EP Safety offices
Marine Ellin, Alexandre Desmarest, Katalin Nikolics, Simon Cherault .
Risk assessment for the underground gallery of
EHN1 – B887
Context: EHN1 safety file edition (887 existing part)
1st step: Identification of gas users (NA 61, SHIP, RE 21, RD 51)
https://indico.cern.ch/event/573690/ and gas suppliers in the area
(EN-EA, TE-CRG)
2nd step: Identification of type of gas: lines, Dewars, bottles,
pressure, quantity.
3rd step: Assessment of the risk: leak scenarios, air flow, condition
of the pipelines
4th step: Engineering check with HSE-XP and main stakeholders
5th step: Approbation of the mitigation measures
Risk analysis: https://edms.cern.ch/document/1728885/2
Risk assessment for the underground gallery of
EHN1 – B887
Galleries volume:
Longitudinal :360m x 3m x 2.5m yielding a volume of 2700 m3
Transversal:7 x (45m x 3m x 2.5m) adding thus a volume of 337.5 m3
Access to gallery
Risk assessment for the underground gallery of
EHN1 – B887
CO2 Gas Bottles
974 m3
Lar Dewar
6000 l
LN2 Dewar
26 850 l
10 bar
Gas network in the gallery
Air circulation : 0 m/s in the longitudinal tunnel and transversal parts
Current fixed ODH detection
Designed for ATLAS exp not anymore in place
Scenario
Leak on N2 pipe (worst case)
Leak on CO2 pipe
No remote analogic monitoring on N2 DEWAR consumption thus undetectable
Leak size
Small (5mm2 )
Medium
(20mm2 )
Large
(500mm2 )
N2
CO2
Time to 18% O2
Time to 19.5% O2 (toxicity)
75.5 h
19 h
62 days longitudinal gallery
7.8 days transversal gallery
16 days longitudinal gallery
48 h transversal gallery
45.8 min
16 hours longitudinal gallery
2 hours transversal gallery
No access control, lack of data on the exposition
Work in the gallery : EN-CV, EN- EL, EP, IT, construction, maintenance
Risk matrix
Gravity of damage for
human body
Exposure average
amount of people
exposed for a year
Minimal
Slights injuries
Low
Temporary
reversible illness
no hospitalization
Medium
Temporary
reversible illness
with hospitalization
High
Death
Permanent disability
Irreversible illness
Permanent
People exposed to the
risk once-twice every day
Often
People exposed to the
risk once-twice every
weeks
Low
People exposed to the
risk once-twice every
month
Exceptional
People exposed to the
risk once-twice a year
Work in gallery
EHN1
Proposed solutions
Action
S
Close access
Reliability
Cost
Timing
Ease of
implemen
tation
Remaining
risk rating
Observation
Need to access the gallery
for operationnal purpose
P-O
Portable ODH and CO2
detectors for every
workers + signs +
IMPACT
Do not cover the CO2
aspect which remains high
in transversal galleries
T
Ventilation in
transversal and
longitudinal gallery +
ODH fix detector +
CO2 fix detectors+
Alarm
Technical specification
need to be done
O
Access control for
galleries
control the awareness; not
the PPEs
T-O
Periodic nondestructive verification
of the pipelines
Assessment to be
performed after each big
work in the gallery
T
Monitoring automatic
on the Dewar and gas
bottle
Difference between small
leak and normal
consumption
Thanks !