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    A Practical Guide to Chemical Safety

    Employers need to be aware of the different risks that face employees as they work with chemicals. This guide explains how employers can raise employee awareness of chemical safety.

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    Introduction to Chemical Safety

    Basic Handling Guidelines

    Most jobs today involve some level of chemical exposure, whether you’re working with hazardous pesticides on a farm, dyeing someone’s hair, mixing compounds in a lab, or cleaning a food preparation area.

    This guide provides a broad overview of approaches to various issues concerning chemical safety at work. The key goal of all workplace chemical awareness information is to reduce exposure to hazardous chemicals and help prevent illnesses, injuries and accidents on the job.

    As a worker in an environment where chemical use is an issue, there are some basic health and safety guidelines that should almost always be followed, regardless of the specific task at hand:

    • Read the relevant Safety Data Sheet (SDS) before working with a chemical product
    • Follow all workplace hazard control plans for hazardous or extremely hazardous chemicals
    • Pay close attention to control measures for chemicals that are known to be a particularly high hazard or chemical carcinogens
    • Never underestimate risk – assume that any mixture will be more hazardous than its most toxic component and that all substances of unknown toxicity are highly toxic
    • Never hold loose items in your mouth, pipette by mouth, or allow lids or soiled protective wear to come into direct contact with skin
    • Never smell chemicals to identify them
    • Do not eat, drink, store food, smoke, or apply cosmetics in areas where chemicals are in use
    • Wash your hands frequently and immediately after any chemical use
    • Keep loose hair tied back and avoid baggy clothing

    Toxicity and DTLs

    The perceived threat to safety – both of employees and the public – involved in workplace chemical use focuses primarily on issues around their potential toxicity.

    For the purposes of health and safety legislation and enforcement, a hazardous chemical’s toxicity rating is often defined in terms of its Dangerous Toxic Load (DTL) value.

    A DTL value expresses the airborne concentration level vs. required exposure time, after which a given chemical causes the Specified Level of Toxicity (SLOT) or Significant Likelihood of Death (SLOD) in the exposed population.

    SLOD is defined as a 50% mortality rate among an exposed population. The HSE has defined the SLOT as any scenario causing:

    • Severe distress to almost everyone exposed
    • A substantial fraction of the exposed population to need medical attention
    • Some incidents of severe injury requiring prolonged treatment
    • The potential for highly susceptible people to be killed

    It’s worth noting that the above SLOT criteria have been kept deliberately broad in scope, to reflect the fact that:

    • There is likely to be considerable variability in the responses of different individuals affected by a major accident
    • There may be pockets of high and low concentrations of a toxic substance in any cloud chemical release, and thus not everyone will suffer the exact same degree of exposure
    • The available toxicity data is not usually adequate for predicting precise dose-response effects
    • They should be straightforward for non-scientists to understand in terms of overall health impact

    Awareness of Risks at Work

    Chemical exposure at work can occur in many different scenarios, both direct and indirect. There will often be very different risks – and levels of risk – for individual employees associated with various processes involving chemicals.

    These might include:

    • Manufacture of chemicals
    • Transport of chemicals
    • Mixing of chemicals
    • Agitation of chemicals
    • Different uses of chemicals in various work tasks
    • Disposal of chemicals

    Safe Disposal of Chemical Waste

    The risk of chemical exposure, either to workers or to the environment, does not always end when handling ends.

    There are numerous basic principles that should always be observed when disposing of chemical waste or leftovers:

    • Know the differences in procedures and requirements for chemical waste classified as hazardous and extremely hazardous, and be aware of the different compliance obligations
    • Designate a hazardous waste disposal area – this should be clearly and prominently labelled, located close to the source of the waste, under the direct and exclusive control of workers in the immediate area, and far removed from other non-chemical activities
    • Choose waste containers that are chemically compatible with the material being placed in them – as a basic rule of thumb, do not store acids or bases in metal, hydrofluoric acid in glass, or solvents in polyethylene containers
    • Use only waste containers with leak-proof, screw-fit caps
    • Wipe down and clearly label waste containers awaiting collection or removal
    • Choose appropriately sized containers for the volume of contents being disposed of – do not underfill, but always leave 10% room for potential expansion
    • Store hazardous waste containers inside a secondary container, to minimize leaking and the potential for incompatible mixes
    • Segregate all incompatible chemical waste (see links and resources for a guide)
    • Do not mix solid and liquid waste
    • Do not combine organic solvents with toxic metal waste
    • Be aware of special packaging requirements for discarded sharps (pipettes, tips, broken glass) alongside chemical waste
    • Be aware of procedures for unknown or unidentified chemical waste – this should always be considered hazardous waste and must be labelled appropriately and handled with caution

    Classification, Labelling and Packaging (CLP)

    Understanding the severity and type of risk depends on classification, labelling and packaging. In a responsible chemical handling workplace, management and workers should know:

    • Chemical legislation applicable to businesses
    • A current inventory of chemicals on site
    • Classification of the substances being handled
    • Comprehensive risk assessment processes
    • Regular monitoring of classification changes and possible impact on compliance status

    Management of Chemical Risks at Work

    Five Steps to Lowering Risk

    There are five core steps in achieving the best approach to reducing chemical hazards for employees in the workplace, listed below in order of preference and efficacy:

    Step one: Elimination of exposure

    This is the first and most desirable step that should be taken wherever possible. If a potentially harmful process, chemical interaction or substance isn’t absolutely essential to achieving the end result, it should be removed from the workflow sequence.

    Step two: Substituting hazardous chemicals or processes

    If wholesale elimination isn’t practical, then substituting potentially harmful chemicals for alternatives that are less toxic or irritant is the next best option. Be aware that some substitutions may introduce new chemical hazards, and must be risk assessed accordingly.

    Step three: Engineering changes

    If a workplace can’t feasibly eliminate OR substitute the risk of harmful chemical exposure, then reducing the threat through designed changes to the physical and mechanical procedures undertaken in the completion of a task should be the next goal. Steps such as improving mechanical extraction, ventilation or disposal methods might be included in possible engineering changes.

    Step four: Administrative changes

    Administrative changes can also be sought to improve hazard management – improved shift and rota systems reduce exposure, provide better supervision or improve training and guidelines publication are all examples of effective administrative changes.

    Step five: PPE

    Personal Protective Equipment (PPE) includes any items of clothing or worn accessories designed to protect users against potential hazards from chemical spill or exposure.

    Although often covered by legal requirements in many work environments, PPE should be thought of as a last line of defence – it’s used to help guard staff against risks that can’t otherwise be eliminated, substituted, engineered or administrated to improve the way a workplace functions or lower the risk of the substances it handles.

    In many specific environments, responsible and legal provision of appropriate PPE equipment is defined by law, but in all cases, it should also be subject to a PPE risk assessment carried out by management in conjunction with employees.

    As well as highlighting areas for improvement in the provision, a comprehensive PPE risk assessment should help establish:

    • Better protocols for understanding limitations
    • Repair and replacement cycles
    • Wearer training
    • Ongoing monitoring of proper PPE equipment use

    Typical PPE supplied in workplaces involving exposure to chemical hazards will include eyewear, gloves, respirators and coveralls, depending on the types and toxicity values of substances present. Full training should always be provided in the correct use of any PPE supplied, as well as clear guidelines on how to safely dispose of single-use items, or clean and reuse non-disposable ones.


    Different chemicals each have their own unique set of risks and hazards associated with them, often dictated by their DTL values.

    Each must be handled appropriately, but in a work environment that regularly handles a wide range of substance types, too many different rules and regulations for each separate chemical can overcomplicate things.

    In the worst-case scenario, this can actually increase the overall risk of accidental exposure or mishandling. As a simplified alternative, it’s worth examining the full range of chemical stock used in a workplace to see if it’s possible to draw up a more wide-scope Standard Operating Procedure (SOP).

    A typical SOP is a range of core regulations that always apply across an entire group of substances, regardless of the specific chemical being handled. SOPs of this sort tend to address general issues such as:

    • Correct use of PPE
    • Responsible handling techniques
    • Communications protocols
    • Emergency procedures
    • Proper disposal techniques

    Once the SOP guidelines have been boiled down to their simplest and most catch-all format, they’ll be much easier for entire teams to learn and act on.

    For any specific chemical hazards that require additional unique protocols, smaller signs or warnings can be placed in suitable locations around the work area.

    Chemical Storage

    Good, safe chemical storage should always begin with taking a comprehensive inventory:

    • Create an accurate and easy-to-reference checklist of all hazardous substances being kept on the premises or in the immediate work area
    • Make sure the inventory is accessible for relevant staff to consult and amend as necessary
    • Check regularly that the inventory and labelling are being kept up-to-date by all users
    • Review the inventory annually; use this as an opportunity to rotate and refresh stock, and to carefully dispose of old, spoiled or unused reserves

    In many workplaces, fines can be incurred by businesses that are unable to present an accurate and current COSHH inventory to certain regulatory bodies, or to emergency service responders in the event of an accident.

    In addition to a vigilant stock-monitoring plan, the three key steps to safe chemical storage are:

    1. Making sure that all potentially hazardous substances are kept in suitable containers and conditions
      1. All container caps and lids should be kept tightly closed at all times when not actively dispensing or topping up
      2. Never leave pipettes, funnels or other items of equipment in the container
      3. Provide drip trays for liquid chemicals in storage (check material compatibility), and provide secondary containers for all liquid chemicals in volumes above one gallon
      4. Use approved containers for flammable solvents
      5. Limit the number of hazardous substances kept in storage to the bare minimum required
      6. Ensure that use-by dates are clearly marked and adhered to
      7. Periodically inspect all stored chemicals – look for signs of:
        1. Leaking
        2. Container damage, either physical or corrosion
        3. Colour changes or darkening
        4. Caking or crystallisation
        5. Pressure build-up
        6. Unclear or missing labels
    2. Making sure that all potentially hazardous substances are stowed in appropriate locations, and that storage areas or environments are properly maintained
      1. Ensure that all chemical storage areas, rooms and cupboards are clearly and accurately marked
      2. Keep storage areas well lit, but avoid direct exposure to heat or sunlight – ensure there is good ventilation with consistent and cool temperatures
      3. Remove all potential sources of ignition from the immediate vicinity
      4. Frequently check on the availability and condition of emergency equipment, wash stations and fire extinguishers
      5. Quickly deal with and remove any leaks or spills
      6. Keep doorways, aisles, walkways and work surfaces in chemical storage areas free from clutter
      7. Regularly check shelving and drip tray setups to maintain stability, levelness and integrity
      8. Use approved corrosive storage cabinets for acids and bases
      9. Use approved flammable storage cabinets for solvents and other combustible chemicals
      10. Minimise the overhead storage of hazardous substances as far as possible, and never store chemicals protruding over shelf edges
      11. Volumes of over one gallon should be stored a maximum of two feet from the ground
      12. Keep corrosive substances below non-corrosive ones
      13. Ensure refrigerators and freezers used for chemical storage are very clearly marked and regularly defrosted to prevent ice build-up
    3. Making sure that all incompatible chemicals are correctly segregated and separated
      1. Chemicals (whether solids, liquids or gases) should always be stored and segregated in accordance with their chemical family or hazard classification, the most types being:
        1. Flammables/combustibles
        2. Corrosive acids
        3. Corrosive bases
        4. Toxics
        5. Highly toxics
        6. Oxidisers
        7. Compressed gases
        8. Cryogens
        9. Pyrophorics
        10. Water reactives
        11. Explosives
      2. Separate each chemical family/hazard classification with an approved non-combustible partition or cabinet, or by a distance of at least 20 feet
      3. Always keep acids and bases separate
      4. Keep most organic acids away from oxidising mineral acids
      5. Keep corrosives away from any potentially reactive substances

    Be aware that many chemicals will belong to more than one family or hazard class – in such cases, observe ALL storage rules for any class that substance fits into, even if it means creating an entirely new storage area for a relatively small volume of chemicals.

    Remain mindful of the four basic types of potential chemical harm:

    1. Flammability
    2. Health damage/toxicity
    3. Reactivity or instability
    4. Volatile incompatibility

    Be aware of the differences between segregation and separation, and when each is an appropriate safety measure.

    General Workplace Housekeeping

    • Keeping floors clean and dry, and promptly removing all forms of chemical spillage, will help prevent slip and fall injuries, as well as keep potential exposure time to a minimum
    • The provision of spill trays or absorbent mats, pads and wiper materials in spill-prone locations is key in enabling staff to clean up spills quickly
    • Placing suitable receptacles for used wiping and absorbency materials near spill-prone sites also helps to minimise exposure times in the event of an accident
    • Continually cleaning and decluttering work surfaces throughout the day reduces the risk of unintended spills and volatile reactions between substances that weren’t intended to be mixed
    • All excess, stored or packaged chemicals should be suitably located away from busy worktops or high-traffic areas, giving staff the room to perform their duties comfortably and reduce the risk of spillage
    • Stockrooms and storage spaces should be well-organised and clearly labelled, with volatile substances suitably segregated – having one person always in charge of stockroom organisation and inventory levels can be helpful in achieving this
    • Clear guidelines and schedules should be established for all forms of chemical waste disposal and maintained through regular checks
    • Training must be provided for all relevant staff in the appropriate disposal methods for any types of chemical they’ll be working with

    Protective Measures and Planning