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Oxidising Agents

INTRODUCTION


Oxidising agents are defined “as substances that react with other materials, either at room temperature or with the application of heat, to cause a type of chemical reaction often involving the bonding of oxygen atoms. Oxidation reactions may be exothermic, proceeding sufficiently vigorously to cause explosions”. Oxidising materials, however, in themselves are not necessarily combustible.


Organic peroxides are particularly hazardous oxidising substances, which are thermally unstable and may exhibit exothermic decomposition.  Where these are encountered, extreme caution is necessary. The properties of such materials in solution may vary considerably depending on the concentration, especially, for example, hydrogen peroxide.

Oxidising agents (e.g. peroxides, chlorates, nitrates, dichromates and permanganates) are widely used in the production of resins and polymers and in other industrial processes, such as bleaching and dyeing, and fibreglass (GRP) moulding, and will also be commonly encountered in laboratories.


The storage and use of oxidizing agents falls within the scope of the Dangerous Substances and Explosive Atmospheres Regulations.

 

RISK ASSESSMENT AND CONTROL


Detailed guidance is contained in RISCAuthority RC43: Recommendations for fire safety in the storage and use of oxidising materials, to which Consultants should refer. HSE publication Guidance Note CS21: The storage and handling of organic peroxides, is a further prime source of reference. The latter document does not cover storage in either tanks or intermediate bulk containers (IBC’s), nor does it apply to formulations which have a peroxide concentration of less than 10%.


Key risk control measures include:


1.      Manufacturer’s Safety Data Sheet (MSDS)

Of paramount importance is the need to ensure that all oxidising agents are stored and handled in strict accordance with the manufacturer’s material safety data sheet (MSDS).

 

2.     DSEAR & COSHH Risk Assessments

All oxidising agents are to be fully recognised within documented DSEAR and COSHH risk assessments and all findings implemented; such risk assessments are to be reviewed when changes in the process occur and at appropriate routine intervals.

 

3.     Information, Instruction & Training

All employees are to be provided with information, instruction and training on the hazards of oxidising agents and the precautions required.

 

4.     Emergency Procedures

The appropriate emergency procedures for dealing with chemical fires, leaks and spillages should be established and documented.

 

5.     Segregation & Storage

Extreme care should be taken with the storage and handling of organic peroxides, with particular emphasis on the following:

 

  • Keep organic peroxides in original containers and hold within the predetermined temperature limits indicated on the MSDS;

  • Maintain records and rotate the stock. Old materials and samples should be disposed of in a safe manner;

  • Store all organic peroxides in designated secure storage facilities. Under no circumstances should flammable liquids be kept in the same area as oxidising agents;

  • Guard against contact/contamination with other materials such as acids, alkalis, accelerators, flammable liquids, combustible materials, reducing agents (e.g. amines), etc.;

  • Strict controls on quantities held in the working area to that sufficient for the job in hand.

  • HSE Guidance Note CS21 prescribes maximum storage quantities for organic peroxides, linked to Flammability Types. Small quantities up to 5kg (Flammability Types 1 & 2) and 10kg (Flammability Type 3) should be kept in a dedicated fire resisting metal cabinet, designed to retain any spillages. For quantities in excess of these amounts, CS21 is very specific as regards dedicated internal or external storage facilities, prescribing requirements for location, construction and a range of other fire safety measures, including a sprinkler deluge system for quantities exceeding 150kg. Reference to the full text of CS21 should be made by Consultants as required.

A typical modern hazardous materials cabinet with a fire resistance rating, depending on the specification, of up to 90min in accordance with BS EN 17440-1: Fire Safety Storage Cabinets.

 

6.      Ventilation

Owing to the volatility of some organic peroxides, an assessment of the ventilation arrangements will require to be made. This will particularly apply to storage areas where a ventilation rate of at least five air changes per hour would be the standard recommendation, achieved via low and high level air bricks or louvres in an external wall, or by suitable mechanical means.

 

7.     Ignition Sources

Potential ignition sources in areas where oxidising agents are stored or handled should be closely scrutinized with particular attention devoted to the following:

 

  • Installation of suitably protected electrical equipment in accordance with the ATEX Directive/DSEAR where applicable (Technical Bulletin 23 refers);     

  • Robust management of hot work/contractors operations;

  • Provision of safe methods of heating, aligned to the environment and the prevailing operations;

  • Installation of temperature monitors and alarms in storage areas;

  • Protection against static electricity (Technical Bulletin 35 refers);

  • The safe use of fork-lift trucks;

  • No Smoking legislation strictly enforced.


8.     Spillages

Oxidising agents should be handled in a manner whereby the risk of spillage is minimised. In the event that a spillage occurs, this should be cleaned up promptly and safely in accordance with a manufacturer’s MSDS. Sawdust should not be employed for swamping spillages which should be dealt with by the use of proprietary, inert absorbent granules that are compatible with the oxidising materials involved, or sand. The peroxide soaked absorbent should be immediately removed to an external metal container and disposed of safely by suitably experienced waste contractor.

 

9.     Dispensing

Dispensing of organic peroxides should take place in a designated dispensing area/room which is kept free of all combustible and incompatible materials. Spillage retention trays should be provided which are capable of holding the entire contents of the peroxide container. Care should also be given to the method of transfer, on which the advice of the materials supplier should be sought.

 

10.     Housekeeping

High standards of housekeeping are essential wherever oxidising materials are stored and handled. Accumulated rubbish should be avoided, and all waste deposited in metal lidded bins, removed from work areas at the end of the working day or shift. Care should be taken not to mix incompatible waste materials.

 

11.     Self-Inspection

Regular formal safety audits should be carried out to ensure that the required standards of fire/health and safety management are maintained.

 

12.     GRP Moulding

Particular care is required when encountering GRP moulding processes in which Methyl Ethyl Ketone Peroxide (MEKP) is commonly employed as a catalyst, traditionally in conjunction with an accelerator. Directly mixing organic peroxide with an accelerator is likely to result in a violent explosion. Therefore, the catalyst should only be added after the resin and accelerator have been thoroughly mixed. Nowadays, whilst the common use of pre-accelerated resins will remove this particular hazard, other flammable liquids, particularly acetone, are likely to remain the vicinity of the mixing operation and the risk of an incident arising from an MEKP spill will continue to be present. 


For small mixing operations, the MEKP catalyst will commonly be dispensed from special plastic bottles incorporating a measuring head. For larger operations, simple wall mounted dispensers are available, together with more advanced resin/catalyst dispensing systems. 


A range of manual, wall mounted catalyst dispensers


A typical resin/catalyst dispensing system powered by compressed air in which resins are drawn from drums or bulk tanks and the catalyst drawn direct from the manufacturer’s container. The unit will dispense pre-set measured quantities of resin, together with catalyst at 0.5% - 4% as required. The dispenser is based on a pair of linked resin and catalyst pumps, powered by an air cylinder and controlled by a mechanical metering device. Suitable for installation in a hazardous atmosphere.


 In cases where GRP spray lay-up processes are encountered, close attention to the potential fire and liability risks will need to be given. In some respects, this may be considered to be a more controlled, cleaner and therefore safer process when compared with traditional bucket mixing and hand lay-up methods.


13.      Fire Extinguishment

Care needs to be taken when fighting fires involving organic peroxides owing to the fact that extinguishers based on smothering, such as foam and CO² will be ineffective. Dry chemical powders containing ammonium compounds are not recommended for use on oxidising agents which might produce chlorine when subject to fire. Specialist advice should be sought to ensure that the correct type of extinguishers are provided (normally water) and that selected staff are adequately trained.

 

Note: This Technical Bulletin should be cross-referenced with Technical Guidance Note 2 ‘The Plastics Industry’.

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