Key learnings from a High Potential Incident
HPI OSH Alert #483
Date of incident: 21 August 2016
A wastewater treatment plant chlorinator had a
chlorine gas leak which set off an alarm at
approximately 6.30am on a Sunday morning. Two operators attended site to verify the alarm. A chlorine
gas leak was confirmed when they observed a plume
of yellow chlorine gas around the chlorinator. The
operators conducted safe job planning and a pre-start
meeting. They tested the safety shower, verified the
leak location with the ammonia puffer and then turned
off the gas. These actions
however do not follow the steps
defined in the procedure for
responding to chlorine gas leaks.
Children were seen 300 metres
away as the operators
approached the site. There is the potential for the
public to get as close as 10 metres to the site.
Why did this happen?
- The cause of the leak was a failed regulator. A speck of rust prevented a gas tight seal from forming
between the needle and the seat. The origin of the rust could not be identified.
- An emergency shutoff device was not fitted at this location, as required by Design Standard (DS) 70.3.The correct procedure was not followed. Water Corporation procedure states not to enter a chlorine
building if chlorine gas is visible.
- A large number of previous false alarms had desensitised the operators.
What will our organisation do to stop this from happening again?
Emergency shutoff device and buffers
- Review all chlorine buffers on a prioritised basis to ensure they are accurate. Assessment of sites will
include a review of any ‘compromised’ buffer zones (i.e. areas that have been/can be encroached upon).
Subsequent actions will be allocated for resolution of any issues identified. The chlorine buffer risk
matrix of Water Corporation’s existing chlorine facilities will be reviewed and updated.
- Review all sites in Water Corporation against the requirement for Emergency Shutoff Devices (ESDs).
ESDs will be fitted at facilities where buffer zones cannot be secured.
Chlorine Leak Sensors
- Confirm the sensitivity of existing sensors and if required investigate and determine the use of more
reliable sensors to prevent false positive alarms for chlorine leaks.
- From findings of the chlorine sensor report, prepare a project brief on how to proceed with replacement
(if any) of chlorine sensors.
Procedure and training
- Review Chlorine Alarm Investigation Procedure and ensure clear instructions regarding the engagement
of DFES are included.
- Ensure relevant training covers how to respond to chlorine leaks (at all levels). Establish training in
LMS and deliver to all relevant staff.
What key learnings can you discuss with your team to stop this from happening
again. Please use the statements and questions below to lead the discussion.
1. In situations where chlorine gas is visible the correct response is to…?
Do not enter the site
- Question 1: What Safe Job Planning should be completed before approaching a site to verify whether
a chlorine alarm is genuine?
- Complete a JSEA – there is no hurry to approach potential danger. Take your time to plan the
- Question 2: What is your response when approaching a site where a chlorine leak is visible?
- Stop and retreat to a safe position upwind and away from the leak.
- Take note of the situation (Who, What, Where, Why) and notify your District Operations
Manager (working hours) or the Region’s Duty Incident Manager (after hours) – or equivalent in
the case of Aroona.
- The OC Operations Control Manager also needs to be notified so that the corporate incident
management process can be activated (All hours).
- Question 3: How will you respond if members of the public are seen in the area?
- Check for your own safety.
- If safe to do so, ask them to retreat to a safe location and indicate the correct path, upwind and
away from the leak.
- Monitor the surroundings while notifying the incident.
2. Buffer Zones:
- Question 1: Does your chlorine site have an adequate buffer for the type of infrastructure?
||Extreme risk infrastructure. Facilities whose buffers have either been compromised and no longer satisfy the EPA Risk Criteria, or are at risk of being compromised in the next two years.
||High risk infrastructure. Facilities whose buffers are at risk of being compromised in the next five years.
||Moderate risk infrastructure. Facilities whose buffers have not been secured but who are not expected to be at risk in the next 5 years.
||Low risk infrastructure. Facilities whose buffers are not expected to be at risk in the long term or have been secured by purchase.
Question 2: Is your site secure and not accessible to the public?
Please contact Senior Engineer – Chemicals Neil Herbert (08) 9420 2562 if you have concerns about your site
not meeting buffer requirements.
If you would like further information about anything included in this HPI OSH Alert, please contact Charis Neumann, Senior OSH Analyst Incidents on (08) 6330 6629.