Storage, Handling and Processing of Dangerous Substances Flashcards
Industrial Chemistry
Raw materials > Primary bulk chemicals > Secondary commercial products
Rate of Reaction in Chemical Production
Quicker it is made the quicker it can be sold
Variables which effect the rate of reaction
Temperature Pressure Concentration Surface area of reactant Catalyst
What is a catalyst?
A substance that alters the rate of reaction without becoming permanently involved in the reaction
Exothermic reactions
Energy is given out by reactants as they form products, causing the temperature of the surroundings to rise
Endothermic reactions
Opposite of exothermic. Energy is taken in by the reactants to form products.
Energy comes from the surroundings which lose energy and cool down, resulting in a drop of temperature
Thermal Runaway reactions
Begins when the heat produced by an exothermic reaction exceeds the heat removed.
Surplus heat raises the temp. of the reaction mass and accelerates the rate of heat production
Risk from thermal runaway
Reaction vessel may become over-pressurised due to violent boiling or rapid gas generation
Harmful effects of thermal runaway
Boiling over of the reaction mass
Large increase in temp. and pressure resulting in explosion
Blast and missile damage
Secondary fires and explosions
Contamination of the wokrplace by hot liquid or toxic materials
Toxic clouds that can spread offsite
Causes of thermal runaway incidents
Inadequate understanding of the process chemistry and thermochemistry
Inadequate design for heat removal
Inadequate control and safety systems
Inadequate operational procedures, including training
HAZOP
Hazard Operability Study - structured method for identifying chemical process hazards
Methods of control to ensure safe operation of Chemical Processes
Inherently safer methods, which eliminate or reduce the hazard
Process control, which prevents a runaway reaction occurring
Protective measures, which limit the consequence of a runaway
Examples of inherently safer methods
Replacing hazardous materials with less hazardous
Having less unreacted material in the reactor, using a continuous process instead of a batch reactor
Using a semi-batch method
Using a heating medium which has a max temp. that is too low for the reaction mixture to decompose
Batch reactors
All reactants are added to a reactor at the start of the reaction. The process stops when chemical reactions are complete
Continuous processes
Reactants continually flow into and products continuously flow out of, the reactor system
Semi-batch methods
Reactants are added in a controlled manner throughout the process. Product is only removed at the end of the reaction
Process control
Includes the use of sensors, alarms, trips and other control systems that either take automatic action, or allow for manual intervention to prevent the conditions for a runaway to occur
Variables controlled in process control
Temperature
Reactant addition
Agitation
Others; PH, conductivity, concentration and pressure
Examples of protective measures
Designing plant to contain maximum pressure
Emergency relief vents
Crash cooling
Reaction inhibitors
Dumping the reaction into a quenching fluid
Legislation covering control of substances that can cause fire and explosions in the workplace
Dangerous Substances and Explosive Atmospheres Regulation 2002 (DESEAR)
Requirement under DESEAR
Employers to assess the risk of fire and explosions that may be caused by dangerous substances in the workplace
Forms of Dangerous Substances
Liquid, gas, vapours or dusts
Dangerous substances include….
Substances covered by CLP regulation
Any dust that when forms a cloud can explode
Any other substances not covered by CLP that could cause a fire or explosion in a workplace (like high flashpoint liquids)
5 steps in a DESEAR risk assessment
- Identify hazards
- Identify who may be harmed and how
- Evaluate risks
- Record significant findings
- Review and revise
Factors to be taken into account in a DESAER Risk assessment
Hazardous properties of the substance
Supplier safety information - SDS on flashpoints and safe method of handling
Circumstances of the work
Particular activities which may be a high level of risk (maintenance and repair tasks)
Likely presence of explosive atmospheres and need for haz. area classification
Hazardous properties of dangerous substances
Size of release
Temperature and pressure
Ventilation
Extent of zones
Other considerations
Purpose of hazardous area classification
Identifies places where controls over ignition sources are needed and determines controls of equipment used in a zone
Relationship between fires and explosions
In many cases where an explosive atmosphere can form, any ignition will cause a fire rather than an explosion. Consideration to be given as to whether the fire could lead to an explosion
Ignition source?
A release of energy often of short duration and localised, which can ignite dangerous substances present in the air
What is an IBC?
Intermediate Bulk Container - cubic container used for transport and storage of fluids and bulk materials. More efficient means of transport than barrels and drums as they can be moved by FLT and stacked
Control measures for the storage of flammable liquids - VICES
Ventilation Ignition Sources Containment Exchange Seperation
Separation Distances
Should allow sufficient time for people to be evacuated and for additional fire fighting equipment and emergency procedures to be mobilised
Min. separation distance for large tanks
At least 16m away from site boundary, any designated non-haz area, process area or any fixed source of ignition
Advantages of underground tanks
Soil provides impact and fire protection
Save space
Separation distances are reduced
Disadvantages of underground tanks
Increased risk of corrosion
Difficult to detect leaks
Soil contamination
Need for confined space access or excavation for all inspection and maintenance
Tank venting system should provide…
Normal pressure relief
Normal vacuum relief
Emergency pressure relief
Types of fire protection for storage tanks
Fire resistant cladding or coating
Fire Walls
Water Cooling Systems
Foam blankets or extinguishing systems
Bonding and earthing
To min. accumulation of electro-static charge and prevent sparks. Required for all metal parts
Flashpoint of flammable liquids which require liquid tight bunding
55 degrees C or below
Sufficient capacity for a bund
Enough to contain largest possible spillage, normally 110% capacity of the largest storage vessel in the bund
Bunding should….
Prevent flamm. liquid or vapour reaching ignition sources
Prevent liquid entering drains and sewers
Allow controlled recovery or treatment of spill
Minimise surface area of liquid
Prevent spread of burning liquids
Prevent contamination of water courses
Particular problems of storing flammable liquids in IBCs in warehouses
Prone to early failure in a fire, allowing leaked contents to feed the fire
Degrade over time so are prone to leak
Generally made of cheap non-conductive plastic so can become electrostatically charged in transit
Principle objectives when establishing a storage compound for drums of flammable/explosive materials
a) Minimise risk of a fire occurring in the storage area itself
b) Protect the store from fires occurring elsewhere
c) Mitigate the consequences of a fire, particularly with regard to people
Hazards of nitrocellulose
Easily ignited and burns fiercely
Emits large amount of heat and toxic fumes
May explode if incorrectly packaged and stored in a confined space
Safe Storage of Drums - Separation
Protects people and property from the effects of a fire in the store itself.
Distances can be reduced if additional fire protection measures such as fire walls are installed
Safe Storage of Drums - Fire resistant storage buildings or storerooms
Such have the following:
Sufficient fire resistance to allow time for the alarm to be raised and for escape
Good means of escape
Lightweight roof or relief panel so that in the event of a fire, escaping heat or fumes are directed to a safe place
Safe Storage of Drums - Control of ignition sources
Prohibit smoking PTW for maintenance involving hot work Control use of electrical equipment Separation from heat sources Protection from exposure to sunlight High standards of housekeeping
Safe Storage of Drums - Restricted access
Authorised people and vehicles only.
High security standards
Safe Storage of Drums - Safety signage
Posted at all entrances.
Type of flammable liquid stored
Smoking and other ignition sources prohibited
Procedure to follow in event of a fire
Section of SDS summarising labelling for CLP
Section 15
Energetic Substances
Capable of releasing energy through rapid exothermic decomposition or polymerisation
Spontaneous Combustion
When the temperature of a substance increases to it’s auto-ignition temperature, at the point it can ignite without an ignition source being needed
Pyrophoric Substances
Spontaneously combust in air or with moisture. Used in semiconductor industry
Types of Automatic Prevention devices for handling dangerous substances
Overflow
Pre-set meter
Fixed volume batch tank
Level detector linked to a pump or valve
Main spray methods
Compressed air - most common
Airless/hydrolic - use for big structures
Electrostatic
Usual way to control flammable vapours and mists when spraying
Ventilated spray booth
Purpose of a ventilated spray booth
Prevent escape of vapours into the workplace
Prevent contamination from overspray
Protect health of workers
Provide separation from sources of ignition and prevent spread of fire
Prevent contamination of workpiece by dust and grease in the work environment
Disposal of flammable liquids
Waste liquids generally need to be stored and handled to the same standards as the flammable liquid they originated from
Dangerous Goods
Liquid or solid substances and articles containing them that have been tested and classified against international criteria and found to be potentially dangerous when carried