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Alarm Flooding

Alarm flooding is a condition where alarms appear on the control panels at a rate faster than the operator can comprehend or deal with. Alarm flooding prevents the operator from determining the cause of the process upset or process emergency and therefore limits the scope for effective and quick emergency response.

Alarm system design and alarm "flooding" of operators trying to deal with excessive numbers of alarms and control rooms was an issue in the Texaco Milford Haven Refinery explosion and fire in 1994 which injured 26 people and caused around £48 million in damages and production losses.

ALARP (as low as reasonably practicable)

This is the level to which risks should be controlled. Thus, determining that risks have been reduced to ALARP involves an assessment of the risk to be avoided, of the sacrifice (in money, time and trouble) involved in taking measures to avoid that risk, and a comparison of the two.

This process can involve varying degrees of rigour which will depend on the nature of the hazard, the extent of the risk and the control measures to be adopted. The more systematic the approach, the more rigorous and more transparent it is to the regulator and other interested parties. However, duty-holders (and the regulator) should not be overburdened if such rigour is not warranted. The greater the initial level of risk under consideration, the greater the degree of rigour the HSE requires of the arguments purporting to show that those risks have been reduced ALARP.

ALARP "gross disproportion" test In any assessment as to whether risks have been reduced ALARP, measures to reduce risk can be ruled out only if the sacrifice involved in taking them would be grossly disproportionate to the benefits of the risk reduction.

For further information on ALARP see website –

Cable Tiles

Cable tiles are lengths of reinforced concrete tiles designed to protect underlying cables and act as depth markers.


Health and safety competence is the combination of knowledge, skills and experience that ensures roles are fulfilled and tasks completed with due regard to the hazards involved and the risk control measures necessary.

Competent Authority

This is a joint inspection and enforcement body consisting of the HSE and either SEPA (in Scotland), or the EA (in England and Wales).

Condensation Induced Water Hammer

"Condensation induced water hammer" is a rapid condensation event. It could also be aptly termed a rapid steam bubble collapse. It occurs when a steam pocket becomes totally entrapped in sub-cooled condensate. As the trapped steam gives up its heat to the surrounding condensate and pipe walls, the steam changes from a vapour to liquid state. As a liquid, the volume formerly occupied by the steam shrinks by a factor ranging from several hundred to over a thousand, depending on the saturated steam pressure. Likewise, the pressure in the void drops to the saturated vapour pressure of the surrounding condensate. (For example, the saturated vapour pressure of condensate at ambient temperature is less than 1 psia).  This leaves a low pressure void in the space formally occupied by the steam. The surrounding condensate still under steam pressure will rush in to fill the void. The resulting collision of condensate generates an over-pressurisation that reverberates throughout the section of pipeline filled with condensate. Since condensate is virtually incompressible, in a collision, it does not give.

The specific factors that influence the severity of condensation induced water hammer are:

(Kirsner: Heating, Power & Air Conditioning Journal: January 1999)".

Construction, Design and Management Regulations 1994 (CDM)

These Regulations are intended to protect the health and safety of people working in construction, and others who may be affected by their activities, by ensuring good management of construction projects, from concept to completion and eventual demolition. Everyone in the construction supply chain is included.

Control of Industrial Major Accident Hazards Regulations 1984 (CIMAH)

The CIMAH Regulations applied to the Complex prior to being superseded by the COMAH Regulations and were designed to prevent or mitigate the effects of major accidents both on people and the environment.

Control of Major Accident Hazards Regulations 1999 (COMAH)

These Regulations superseded the CIMAH Regulations in 1999 and extended the scope and requirements in line with the Seveso II Directive.  Major accident hazard sites as defined under the COMAH Regulations (COMAH sites) are required to prepare and submit a safety report to the Competent Authority for assessment which should contain certain information as specified by the regulations in order to allow the Competent Authority to assess the overall safety of the site.

Control of Major Accident Hazards Regulations 1999 (COMAH) - Regulation 4

Regulation 4 requires that "Every operator shall take all measures necessary to prevent major accidents and limit their consequences to persons and the environment".

Control of Major Accident Hazards Regulations 1999 (COMAH) - Regulation 18

Regulation 18 requires the Competent Authority to prohibit operation if serious deficiencies with major accident potential are found.

"The competent authority shall prohibit the operation or bringing into operation of any establishment or installation or any part thereof where the measures taken by the operator for the prevention and mitigation of major accidents are seriously deficient".

Control of Major Accident Hazards Regulations 1999 (COMAH) - Regulation 19

Regulation 19 of the COMAH Regulations clearly identifies the inspection and investigation duties of the Competent Authority and states:

  1. "The competent authority shall organise an adequate system of inspections of establishments or other measures of control appropriate to the type of establishment concerned;
  2. The inspections or control measures referred to in paragraph (1) shall not be dependent upon the receipt of any report submitted by the operator and they shall be sufficient for a planned and systematic examination of the systems being employed at the establishment, whether of a technical, organisational or managerial nature;
    1. that the operator can demonstrate that he has taken appropriate measures to prevent major accidents;
    2. that the operator can demonstrate that he has provided appropriate means for limiting the consequences of major accidents both inside and outside the establishment;
    3. that the information contained in any report sent to the competent authority by the operator of the establishment adequately reflects the conditions in the establishment; and
    4. that the information has been supplied to the public pursuant to regulation 14.
  3. A system of inspection referred to in paragraph (1) shall meet the following conditions –
    1. there shall be a programme of inspections for all establishments;
    2. unless such a programme is based upon a systematic appraisal of major accident hazards of the particular establishment concerned, the programme shall, in the case of establishments to which regulations 7 to 14 apply, entail at least one on-site inspection made on behalf of the competent authority every 12 months;
    3. following each inspection, a report shall be prepared by the competent authority; and
    4. where necessary, matters shall be pursued with the operator within a reasonable period following the inspection.
  4. Where the competent authority or the Executive has been informed of a major accident at an establishment the competent authority shall –
    1. obtain from the operator of the establishment –
      1. information as respects the circumstances of the accident, the dangerous substances involved, the data available for assessing the  effects of the accident on persons and the environment, the emergency measures taken and the steps envisaged to alleviate the medium and long-term effects of the accident and to prevent any recurrence of it, and
      2. such other information in the operator’s possession as will enable the competent authority to notify the European Commission pursuant to regulation 21(1);
    2. ensure that any urgent, medium and long-term measures which may prove necessary are taken;
    3. make a full analysis of the technical, organisational and managerial aspects of the major accident and collect, by inspection, investigation or other appropriate means, the information necessary for that purpose;
    4. take appropriate action to ensure that the operator takes any necessary remedial measures;
    5. make recommendations on future preventative measures."


A process by which molecules with many carbon atoms are broken down into smaller molecules with fewer carbon atoms.

DCS - Distributed Control Systems

An electronic process control system where the control of a unit is split between user interfaces (which may be remote from the unit) and the electronic control equipment, which is typically located on the process unit.


A section of pipe where there is normally no flow and which is filled with stagnant process fluid.

Electricity at Work Regulations (EWR) 1989

These Regulations impose duties on persons in respect of electrical systems, electrical equipment and conductors and in respect of work activities on or near electrical equipment in order to ensure, as far as is reasonably practicable, that there is no danger of death or personal injury.

Environmental Protection Act/Integrated Pollution Control

Under the IPC Regulations sites are required to prepare and submit IPC applications to SEPA for assessment. These IPC applications should contain certain information as specified by the regulations in order to allow the SEPA to assess the environmental performance of the facilities on-site. Following submission of a successful IPC application SEPA will then issue an IPC authorisation. IPC authorisations include the approved discharge points and the quantities and compositions of the authorised emissions. The authorisation may also contain an improvement programme for the company to follow with, for example, specified dates for the installation of new equipment or the preparation of a technical report.


Flare stacks are used to burn-off materials that are generated on-site but which can not be re-used or reclaimed. Under normal operating conditions a bright orange flame can be seen coming from a flare stack. However if the combustion conditions are not optimised then dark smoke can be seen being released from the flare stack.

FCCU - Fluidised Catalytic Cracker Unit

A refinery unit using a widely-used process for the conversion of the heaviest components of crude oil into motor fuels.

Grangemouth Petrochemical Complex Major Incident Control Committee

The Grangemouth Petrochemical Complex Major Incident Control Committee (MICC) was set up in the late 1960’s and has successfully developed an integrated emergency management plan which consists of Procedures for Dealing with a Major Incident at Grangemouth (the MICC Procedures) and Falkirk Council’s statutory COMAH Off-site Contingency Plan for the mitigation of a major industrial accident at Grangemouth. The MICC Procedures are based on a mutual aid scheme between the petroleum, chemical and related industries together in partnership with Falkirk Council, and the emergency services, the Health Board, the Water Authority and the COMAH Competent Authority.

The MICC provides a link between the on-site emergency plans of the establishments in the Grangemouth area (Avecia, BP, Syngenta, Calor Gas etc.) and the statutory off-site plans drawn up by Falkirk Council. It provides resources as necessary and in the event of an incident provides communications between the companies, the public authorities and the general public. It includes technical experts and representatives from local major hazard sites, police and emergency services, the Local Authority, public health and the utility companies.

Health and Safety at Work Act etc. 1974 (HSWA)

The HSWA lays down a framework of duties for ensuring health and safety. The Act imposes general duties on employers towards employees and others, including members of the public off-site, to ensure that they are protected from the risks arising from the employers’ activities.

Health and Safety at Work Act - Section 3

Section 3 of the Act places a duty on employers to ensure, so far as is reasonably practicable, that people who are not employed by them, but who may be affected by the way they conduct their business, are not exposed to risks to their health and safety.

Human Factors

Human factors discovers and applies information about human behaviour, abilities, limitations, and other characteristics to the design of tools, machines, systems, tasks, jobs, and environments for productive, safe, comfortable, and effective human use.

IMT - Incident Management Team

A BP Grangemouth multi-disciplinary team established in accordance with emergency procedures to advise and manage the emergency response to an incident.

Level 1 Investigation

A "Level 1" investigation refers to an investigation carried out when there is high level of interest amongst the local population, politicians etc. but where there have been no fatalities. "Level 2" investigations are appropriate when fatalities have resulted. "Level 0" investigations are appropriate when there has been a "near miss".

This was terminology used in HSE/HID Major Incident Procedures at the time of the incidents, but has now been superseded by another categorisation approach.

Logistics Facilities

Logistics refers to storage and distribution facilities such as warehouses, loading areas etc.

Major Accident

An occurrence (including in particular, a major emission, fire or explosion) resulting from uncontrolled developments in the course of the operation of any establishment and leading to serious danger to human health or the environment, immediate or delayed, inside or outside the establishment, and involving one or more dangerous substances.

Major Accident Hazard Sites

These designated sites process or store more than specified quantities of certain dangerous substances and have the potential to cause significant on-site and off-site effects to employees, members of the public and the wider environment including the possibility of causing multiple fatalities. The quantities stored at Grangemouth are in excess of the Top Tier thresholds as defined under the COMAH Regulations and therefore the Complex is subject to the full requirements of the COMAH Regulations.

Management of Health and Safety at Work Regulations 1999

These Regulations are aimed at improving health and safety management, and make more explicit what is required of employers under the Health & Safety at Work etc. Act 1974. They lay down a framework of duties requiring a systematic approach to the management of health and safety, based on risk assessment.


A permit-to-work system is a formal written system used to control certain types of work that are potentially hazardous. A permit-to-work is a document which specifies the work to be done and the precautions to be taken. Permits-to-work form an essential part of safe systems of work for many maintenance activities. They allow work to start only after safe procedures have been defined and they provide a clear record that all foreseeable hazards have been considered.

Pressure Systems Safety Regulations 2000 (PSSR)

These safety regulations deal with the stored energy hazards associated with the containment of fluids under pressure, in pressure equipment and systems – for example boilers – used in the workplace. The aim of the PSSR is to prevent serious injury from the hazard of stored energy as a result of the failure of a pressure system or one of its components.

Process Safety Management

Process safety management is concerned with the management of safety hazards arising from process operations and is distinct from the management of conventional safety (slips, trips, falls etc). Process safety management requires detailed knowledge of the chemical and process hazards associated with the operations of the plant in order to ensure that the correct focus and resource is applied to the control of the potential major hazards.

Remotely Operated Shut-Off Valve (ROSOV)

A valve which allows an item of plant or equipment to be isolated automatically from a safe location without the necessity for manual intervention.

The inability to quickly isolate hazardous substances inventory in the event of a major accident was an issue in the Associated Octel Company

major accident (1st and 2nd February 1994). 

For new installations ROSOVs should normally be fitted unless there are good technical reasons why they are not appropriate.  For existing installations, the decision needs to be based on ALARP/cost benefit analysis.


The Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 places a legal duty on employers, the self-employed and those in control of premises to report some work-related accidents, diseases and dangerous occurrences to the relevant enforcing authority for their work activity. This can be either the HSE or one of the Local Authorities.

The law requires the following work-related incidents to be reported:

Set-on Tee

A tee-piece which is formed by welding one pipe over a hole made in another. In this case the tee-piece is formed by the pipes themselves with the joining weld being at the junction of the tee-piece. This is distinct from a forged weld-reducing tee-piece where the junction is in the forged fitting and is at a distance from the welds between the fitting and the adjoining pipes.

diagram of a forged welding reduced tee piece

Seveso II Directive

The Seveso II Directive has two aims. Firstly the prevention of major accident hazards involving dangerous substances and secondly (since accidents do occur) the limitation of the consequences of such accidents not only for man (health and safety aspects) but also for the environment. The requirements of the Directive are incorporated into UK legislation by the COMAH Regulations.

Steam Trap

A device installed in steam distribution systems which removes hot condensate from the steam main in order to protect the steam main from condensate build-up. Discharge of hot condensate from a steam trap may be directly to the environment or into a condensate collection system if appropriate. Different types of steam trap are available for installation.

TLC - The Total Loss Control System

A computer based system for recording and ranking incidents and near-misses on the BP Grangemouth Complex and for tracking actions resulting from such incidents and near-misses.

Top Tier/Lower Tier

The COMAH Regulations operate at two levels depending on the quantities of dangerous substances at an establishment. Schedules of specific "named substances" and "general categories" are presented in the Regulations.

Establishments which have quantities of dangerous substances exceeding the top tier thresholds (either individually or following application of the COMAH aggregation rules) are known as "top tier" COMAH sites. "Top tier" status requires the operator to:

Establishments which have quantities of dangerous substances exceeding the lower tier thresholds (either individually or following application of the COMAH aggregation rules) but not the top tier thresholds are known as "lower tier" COMAH sites. "Lower tier" status requires the operator to:-

Water Hammer

When a column of flowing fluid is suddenly stopped, a pounding of the line commonly known as water hammer is usually produced.


A forged tee-piece where the joining pipes are each welded to the fitting but where the forged fitting forms the actual tee-piece.

diagram of a forged tee piece where the joining pipes are welded to the fitting

Vapour Cloud Explosion

A cloud of vapours which when ignited can not expand freely results a significant overpressure and explosion.

In general terms explosions tend to be more serious since they have the potential to cause fatalities more readily than fires due to the short duration energy release which gives no time for evasive action to be taken by personnel. In the event of a fire, escape is often possible due to the time taken for the spread of the fire to occur.

VRU - Vapour Recovery Unit

The section of the FCCU where the light hydrocarbon gases produced by the cracking process are compressed and separated into different product streams.