What you need to know
Guidance: what you need to know – DSEAR controls
In the last issue of
Connect we looked at the background to the Dangerous
Substances and Explosive Atmospheres Regulations 2002 (DSEAR) and
their requirements for dividing workplace areas into zones
according to the type of explosive atmosphere that could occur, and
the likelihood, frequency and duration of the explosive atmosphere.
In part two on the topic of DSEAR, we look in more detail at risk
assessment, control measures and training.
Headlines
What are dangerous substances?
The previous article on the
background to DSEAR explained that when discussing DSEAR, the term
“dangerous substance” specifically refers to substances or
preparations that could cause harm to people at work as a result of
explosive, oxidising or flammable properties, whether or not the
substance is classified under the Chemicals
(Hazard Information and Packaging for Supply) Regulations 2002
(CHIP regulations).
Dangerous substances include:
- obviously flammable substances such as petrol and liquefied
petroleum gas (LPG)
- substances used for other purposes which are also flammable
under certain conditions such as paint, varnish, solvents
- dusts which can become explosive when mixed with air, for
example dust created from milling, sieving, or sanding operations,
including sugar, flour, coal, wood, certain metals (such as
aluminium and magnesium) and many synthetic organic chemicals
- materials which are normally stable, but which may self-heat
because of oxidation (eg oil, plastic, wood, sawdust) or
bacteriological action (eg fermentation of grain, sugar or straw,
especially if they’re allowed to get wet).
The Approved
Classification and Labelling Guide (L131) provides more
detail on how substances are classified as explosive, oxidising,
extremely flammable, highly flammable or flammable, with risk
phrases associated with each category. For example, risk phrases R2
and R3 refer to the risk and the “extreme risk” of explosion by
shock, friction, fire or other sources of ignition, and they apply
to substances such as organic peroxides. R6 refers to substances
which are explosive with or without contact with air at ambient
temperatures (such as acetylene) and R7, which indicates “may cause
fire,” applies to reactive substances and preparations such as
fluorine.
Dangerous substances can be in the form of liquids, gases and
solids. Substances which aren’t dangerous as a large solid can
become explosive when in the form of dust. Different advice is
available for each class of dangerous substance.
Liquids
The following specific advice is available from the HSE on
flammable liquids:
These two documents deal specifically with petrol:
Gases
The following advice is available from the HSE on dangerous
substances in the form of gases:
For additional information, look at the European Industrial
Gases Association (EIGA) safety leaflets:
Dust
Dust may not be such an obvious hazard to inexperienced workers,
so information, instruction and training will be particularly
important.
Since fire requires oxygen to continue to burn, a solid material
will burn relatively slowly, as there’s a limited surface area
exposed to the air. If the same solid is in the form of a cloud of
dust, there’s a much greater surface area exposed to the air, so if
there’s an ignition source the cloud will burn much more quickly
than the corresponding solid mass would have done.
Measures to reduce the risk of explosion from dust clouds are
explained in the HSE publication HSG103 Safe
handling of combustible dusts: Precautions against
explosions under four headings:
- controls over dust cloud formation (eg dampening, using pellets
rather than dust)
- preventing the explosive atmosphere by inerting (that is,
supplying an inert gas into an enclosed space)
- avoiding ignition sources (eg through the control of ‘hot work’
and the control of equipment used in zoned areas)
- plant design and controls (eg dust collection, air monitoring,
spill alarms).
HS(G) 103 also describes mitigation measures, such as explosion
relief venting. A second guidance document, HSG131
Energetic and spontaneously combustible substances:
Identification and safe handling includes
advice on the storage, manufacture and use of dusts.
Information from the HSE specifically on controlling dust
explosions in the food industry is available here.
If you’ve time, the US Chemical Safety Board (CSB) report on the
2008 sugar refinery explosion is worth a read for its
list of failures and suggested controls. It includes
photographs which you could use to demonstrate to any doubters the
explosive properties of sugar.
Risk assessment and management
The British Compressed Gases Association (BCGA) has detailed
guidance on how to conduct a DSEAR risk assessment in
Guidance Note 13
(GN13). GN13 explains how to carry out each of the
following stages:
- identify dangerous substances
- identify potential sources of release, using criteria including
location, likelihood, operating conditions, ventilation
- produce a zone map showing the zone type (from DSEAR Schedule
2) and the vertical and horizontal zone extent
- identify potential ignition sources (heat, mechanical,
chemical, electrical)
- assess the likelihood of ignition occurring
- calculate an overall likelihood of explosion (ie the product of
the likelihood of a flammable atmosphere and the likelihood of
ignition)
- describe the consequences of any fire or explosion.
Schedule 1 of DSEAR specifies general safety measures to
eliminate or reduce risks from dangerous substances. These
include:
- design, construction and maintenance of the workplace
- design, construction, assembly, installation, provision,
maintenance and use of suitable work processes
- provision and maintenance of “fail safe”, manual override and
emergency shutdown systems for equipment and protective
systems
- written instructions for tasks
- use of a permit to
work system.
Arrangements to deal with incidents and emergencies
Regulation 6 (3)
of DSEAR requires that while all practical steps should be
taken to prevent an incident, measures should also be taken to
reduce the damaging effects of a fire or explosion should it occur.
Such steps include:
- reducing the number of employees exposed
- explosion
pressure relief and explosion suppression
- containment of fires and explosions
- as a last resort, the provision of suitable personal protective
equipment (PPE).
There should be suitable warning and communication systems in place
(including visual and audible alarms) as well as emergency and
escape procedures which have been tested through practical
exercises, and are rehearsed as often as the risk assessment
requires.
The HSE has an Approved Code of Practice (ACoP) dedicated to this
aspect of DSEAR in L136 Control and mitigation measures. This
divides its advice on mitigation into three areas:
1) Ventilation, including natural and
artificial (or forced) ventilation – in order to maintain the
average concentration of dangerous substances below that which
could form an explosive atmosphere, ventilation must be monitored
to ensure no blockages occur which could reduce the flow of air.
Further HSE advice on ventilation is available in HSG258
Controlling airborne contaminants at work: A guide to local
exhaust ventilation (LEV).
2) Ignition control measures, which include:
- Select and install appropriate electrical and non-electrical
equipment that’s been designed to be safe in hazardous areas (and
meets the Equipment
and Protective Systems for Use in Potentially Explosive Atmospheres
Regulations 1996 (EPS), as amended).
- Implement inspection, testing, cleaning and maintenance regimes
to minimise overheating and to minimise any fault conditions which
could result in an ignition source.
- Make sure that any portable or mobile equipment brought into
hazardous areas is suitably protected, or use a permit to work
scheme to control conditions.
- Prohibit smoking and other open flames.
- Implement controls and procedures to prevent hazardous
electrostatic discharges.
- Make sure heating equipment cannot act as an ignition
source.
- Place waste materials in a closed metal bin or remove them to a
safe place. Don’t allow the accumulation of waste materials or
deposits that are liable to spontaneously combust or are readily
ignited.
- Avoid incompatible materials that could react together to
produce heat or flames or that could give rise to sparks
following frictional contact during impact, machining, grinding or
polishing.
3) Separation, which can be achieved by distance. If space is
available, adequate separation may be achieved solely by the actual
distance between the dangerous substance and the feature that is to
be protected, or protected against. However, where distance is not
sufficient, there need to be physical barriers. These need to be
capable of maintaining adequate fire protection to allow time for
evacuation and for implementation of emergency procedures.
Paragraphs 74 to 105 and appendix A of L136 provide more detail on
the specification for physical barriers, but in general fire
resistance should last at least 30 minutes, or 60 minutes if there
are vulnerable people or other non-employees at risk.
Information, instruction and training
Regulation 9 of
DSEAR outlines the requirements for information, instruction
and training if a dangerous substance is present in the workplace.
Workers may be unaware of the explosive nature of common substances
(particularly food dusts). Information, instruction and training
should cover:
- the names of the dangerous substances in use and the risks they
present
- access to relevant safety data sheets
- appropriate precautions and actions to be taken
- significant findings of the risk assessment.
As with any training, it should be reviewed when work methods or
equipment change and it should take account of the results of
relevant risk assessments.
Standards
The standards BS
EN 60079-10-1:2009 Classification of areas: Explosive gas
atmospheres and
BS EN 60079-10-2:2009 Classification of areas: Combustible dust
atmospheres explain the procedures for area classification
for explosive gas and combustible dust atmospheres, and provide the
criteria against which ignition hazards can be assessed. Guidance
is provided on the design and control features that apply to each
hazardous area type.
Further HSE advice
The following HSE documents provide advice on specific
situations relating to potentially flammable or explosive
atmospheres:
IOSH links