OPSIS - notification limit exceedings

These are the incidences where the OPSIS monitoring notification limit was exceeded since the start of the system at BP in Geel in April 2000.

By way of the detection system OPSIS, BP continually monitors the presence of hydrocarbons such as benzene around the PX unit. BP has agreed with the authorities to notify the 'Milieu-inspectie' (Environmental Inspectorate) and a number of public bodies the moment the system measures a value exceeding 100 microgram per cubic metre for more than 30 minutes. The amount of 100 micrograms per cubic metre is called the notification limit.
Since the system was launched at BP in Geel in April 2000, the OPSIS detection system has recorded these occasions so far: 


  • Date: 23-07-2000
  • Registered peak: 131,9 micrograms per cubic meter
  • Situation: The incident occurred during preparatory maintenance work. Before maintenance work can be carried out on a pump, all residues of the pumped product have to be removed. The pump in question was washed with nitrogen in order to make it benzene-free, but this seems to have been done insufficiently. Benzene escaped and this was picked up by OPSIS .
  • Remedy: The procedure for making equipment benzene-free has been made stricter.


  • Date: 30-11-2000
  • Registered peak: 345 micrograms per cubic meter
  • Situation: As part of a planned maintenance shutdown, a section of the PX unit was purged of hydrocarbons. This was done by "pressing" liquid, by means of nitrogen, from process vessels into a closed drainage system. This system converges in the collection drum PD 1801 where water was separated from hydrocarbons (such as benzene). The water then was drained off to the waste water unit, whereas hydrocarbons were led to a buffer vessel. Because of an unforeseen pressure increase, this buffer vessel overflowed and part of the hydrocarbons ended up in the waste water unit. This resulted in a benzene release to the atmosphere.
  • Remedy: The separation process was abolished. Water and hydrocarbons now flow together to the entirely closed buffer vessel.


  • Date: 21-04-2001
  • Registered peak: 150 micrograms per cubic meter
  • Situation: At about 7.30 o'clock (7.30 AM), OPSIS notified the control room of a peaking benzene value in the south-western (SW) path. A check revealed a leaking seal on pump PG107B.
  • Remedy: A spare pump was immediately put in operation. The failing pump was flushed and liquids were led into the closed drainage system. The spilled liquid was removed with a suitable absorption material.


  • Date: 09-01-2003
  • Registered peak: 363 micrograms per cubic meter on the SW side
  • Situation: Due to frost, a connection between a vessel (fuel gas drum) and a closed draining system was blocked. The vessel holds excess gasses and fluids. Because of the build-up the level rose excessively in the vessel which alerted personnel. They had no other choice but to drain an amount of the content into an open 200 litre vessel, causing a temporary excess of benzene into the atmosphere.
  • Remedy: BP personnel immediately thawed the blocked connection by means of steam. To avoid recurrence, a so-called tracing was installed on critical parts of the draining system. Tracing are conduits which are heated by steam or electricity.

5th, 6th, 7th

  • Dates : 03-08-2003, 13-08-2003 and 16-09-2003
  • Registered peaks: 102, 112 and 107.9 micrograms per cubic meter
  • Situation: In the PX unit several vessels serve as intermediate buffer for fluids. These vessels are partially filled with product. Right above the fluid, there is vapour. Because of high atmospheric temperature, the vapour expanded, causing excessive pressure built-up, followed by increased emissions.
  • Remedy: The vents of the tanks linked with the PX unit, which caused the exceedings, will be connected with a closed drain system. This project will be executed in the summer of 2004.


  • Date: 04-07-2004
  • Registered peak: 152. 5 and 126.5 micrograms per cubic meter
  • Situation: To reduce water usage during the start-up of the PTA3 unit, a different start-up procedure was used. This has caused an exceeding benzene emission via the central chimney.
  • Remedy: Process conditions will be changed to avoid benzene formation during a future start-up.


  • 20-09-2005
  • Registered peak:: 191 micrograms per cubic meter
  • Situation: When cleaning a high pressure cleaning device (during a maintenance stop), a small quantity of product was released. This caused OPSIS to register elevated benzene values during a short period of time.
  • Remedy: Work was halted immediately. During monitoring on the spot no more elevated benzene values could be registered anymore.


  • Date: 02-01-2009
  • Registered peak:: 230.5 micrograms per cubic meter
  • Situation: The peak was measured on the northeastern path during a north-east to south-west wind. Operators immediately executed additional measurements in the unit with a portable device. However even further investigation could not establish a direct cause in the PX unit. It cannot be excluded that the peak may be caused by an external source.
  • Remedy: None


  • Date: 28-12-2009
  • Registered peak: 480 micrograms per cubic meter
  • Situation: The increased OPSIS value was caused by a flow transmitter leak within the PX unit. The emission remained local and the increased OPSIS measurement was to a large extent caused by weather conditions (inversion, lack of wind).
  • Remedy: The device was immediately taken out of service and has been repaired since.


  • Date: 12-12-2010
  • Registered peak:: 108 micrograms per cubic meter
  • Situation: The increased OPSIS value was monitored on the north east path. The wind came from the north west
  • Remedy: Operators have immediately executed additional measurements with a portable device. No direct reason for the exceeding within the PX unit was detectable.


  • Date: 15-11-2011
  • Registered peak: 128 micrograms per cubic meter
  • Situation: The peak was registered during maintenance work, more specifically whilst placing blinds near the collection drum of the closed drain system. During this action, a short-lived emission was registered.
  • Remedy: None.


  • Date: 06-03-2013
  • Registered peak: 110 microgram per cubic meter
  • Situation: After this peak was registered by OPSIS, BP has executed extra measurements in the unit by means of a portable device. No other increased values were established. However, there are clear indications that the source of the increased value is to be situated outside of the site.
  • Remedy: None.


  • Date: 15-06-2014
  • Registered peak: 139.8 micrograms per cubic meter
  • Situation: During a maintenance stop, an incorrectly sealed waste barrel was found near a control shelter in the PX unit. Whilst lifting the cover to check if the barrel was being used, some product may have escaped.
  • Remedy: The barrel was immediately closed again in a correct fashion.


  • Date: 16-06-2014
  • Registered peak: 126 micrograms per cubic meter
  • Situation: During a maintenance stop whilst working on pumps near the PX tank farm, a limited amount of benzene was released.
  • Remedy: Absorption with turf and nitrogen flushing.


  • Date: 17-06-2014
  • Registered peak: 234 micrograms per cubic meter
  • Situation: During a maintenance stop, catalyst is being regenerated. During the start-up of the catalyst regeneration, some benzene emission occurred.
  • Remedy: The emission was lined up to flare.


  • Date: 26-06-2014
  • Registered peak: 135.4 micrograms per cubic meter
  • Situation: Near the OPSIS measuring track, a contractor executed coating activities. The cleaning product used to do this contained naphtha. During the activities, a petrol driven generator was used.
  • Remedy: The activities were halted.


In 2015 no exceedances of the information threshold were observed.


In 2016 no exceedances of the information threshold were observed.