Dyes and dyeing
Exposure to dyes
Dyes used in textile finishing have many different, complex chemical structures and there are many products in commercial use. Uncontrolled exposure to some hazardous dyestuffs is clearly recognised as potentially harmful to health; but there are a very large number of dyes that have not been associated with any adverse health effects. It is possible that, for a small number of these, adverse effects on health can occur but have not yet been detected; however, it is unlikely we will ever have complete knowledge of all the hazards of dyes. So it is prudent to minimise exposure to dyes of all types, even if no adverse health effects are known.
Some reactive dyes are recognised respiratory sensitisers. Breathing in respiratory sensitisers can cause occupational asthma and, once a person is sensitised, re-exposure to even very small amounts of the same dye may result in allergic symptoms such as a runny or stuffy nose, watery or prickly eyes, wheezing, chest tightness and breathlessness. Some dyes can cause allergic skin reactions. Certain reactive, vat and disperse dyes are recognised skin sensitisers.
A small number of dyes, based on the chemical benzidine, are thought to cause cancer – there are substitutes for these dyes in textile use.
Other dyes may also present hazards to health. It is essential to read the safety data sheet supplied with each hazardous product.
Adding sodium hydrosulphite, also known as sodium dithionite or 'hydros' to process vessels can cause serious injuries. This generally happens when the substance has been added too quickly and has solidified into a plug. The reaction is often so violent it causes the contents to erupt over the side of the vessel. To avoid this, take these precautions:
- Ensure a safe system of work for adding hydros, particularly for cleaning dye vessels
- Do not add hydros to an item of plant that has previously contained an oxidising agent such as hydrogen peroxide unless it has been rinsed thoroughly first
- Always dispense hydros into clean, dry containers
- Ensure adequate ventilation to remove sulphur dioxide fumes that are likely to be created when hydros is cooled.
- Always make sure hydros is adequately diluted and that any lumps are broken up
- Consider fixing a mechanical mixer to any vessel that regularly has hydros introduced to it
Safe handling of dyestuffs
- Consider if there are less hazardous forms of the dyestuffs available. Choosing low-dusting dyes such as those in granular, dust-suppressed or liquid form can be a very important factor in reducing exposure. Remember that even liquid dyes can cause dust problems if spills are allowed to dry out
- Monitor batches of powdered dyestuffs closely and consider returning any unduly dusty product to the supplier
- Restrict access to the colour store to essential trained personnel. In some dyehouses, each dyer weighs their own dye and this tends to increase the chances of spillage and reduce the standards of housekeeping. It is better to have only one or two people do all the weighing, with proper training and precautions
- RPE should always be considered as a last resort:
- a number of factors can seriously affect its performance, so the protection afforded to the employee decreases dramatically, eg if a respirator is badly maintained, contaminated with dyestuff, not properly adjusted to the wearer or removed for even short periods while dust is airborne
- RPE does not protect against skin irritation
- wearing RPE all day may cause undue stress and discomfort to the wearer.
Identifying sources of exposure
The major route of personal exposure is inhalation of dye dust. This can happen at many stages in the handling process, eg when opening dyestuff containers or cleaning spillages
Another exposure route is dyes being in contact with skin. Harsh skin cleaning to remove colour may cause dermatitis
To reduce the risk to health from dyestuffs effectively, you need to identify, assess and control all sources of significant exposure. Some sources of exposure typical to a textile dyehouse are given below
Preventing secondary exposure to dust from settled deposits
- Walls should be smooth and impervious. At the very least, brick or breeze block surfaces should be sealed with a gloss finish
- The store should be well lit
- Floors should be smooth, but non-slip, with well-sited floor drains
- Raise dye containers at least 300 mm off the floor to make floor cleaning easier
- All surfaces should be easy to wash down and should be free from recesses or ledges, which trap dust. Unfinished wooden or rusty metal surfaces are impossible to keep very clean
- Make sure access to stored materials isn’t blocked
- Remove all extraneous items or keep them in cupboards with well-fitting doors
- People gather dust too! Provide non-dust-retaining overalls and head covers
- Provide separate accommodation for protective and personal clothing to prevent cross-contamination. Provide at least one change, so they can be washed when contaminated
- Wash overalls on site or at a commercial laundry alerted to the risk of exposure from contaminated clothing
- Set up ventilation so air changes take place without creating draughts, which may disturb settled dust
- Put in place a regular programme of cleaning
- Prohibit eating, drinking and smoking in areas where dyes are handled
Opening and resealing containers and scooping powder
Dust clouds are raised:
- when dye container lids are removed and replaced
- when dye is scooped from containers
- when scoops are carried to and from weigh scales
- when pellets or granules are dropped on the floor and trodden down to fine dispersible dust
Once dust is generated, the fine inhalable particles stay airborne for a long time. Therefore, it is highly recommended that dispensing takes place under local exhaust ventilation - this usually means in the weighing booth. To make this easier:
- Provide wheeled trolleys or mount large dye drums on castors, so containers can be easily pushed to the booth. Don’t forget to assess any risks from manual handling
- Organise your store so that ‘fast-moving’ products, particularly dusty dyes and dyes with recognised hazards to health, are nearest the booth. Some items may be kept permanently in the booth if it is large enough
- Use ventilated carousels which can be rotated to present the appropriate drum to the weighing station
When refurbishing or planning a new facility, consider different options to the traditional method of storage. These might include paternosters - rotary stores in which the shelves holding the dye drums are brought round to the weighing station. The ventilated weighing station itself may be made mobile, guided on rails by the operator to the appropriate place on the shelf. Robotic handling is employed in some dyehouses.
In some colour stores, dispensing all dyestuffs in the ventilated weighing room may not be practicable. An example might include a commission dyehouse with a very large inventory of dyes, only a few grams of which are often needed at any one time. In these circumstances:
- while it may not be practicable to take all dyes to the weigh station, the colour weigher should still take as many there as possible. Organise your store as above
- reactive dyes, benzidine-based dyes and those with an ‘X Harmful’ or skull and crossbones label should always be dispensed under local exhaust ventilation, regardless of the quantity involved
- scoops should be of an adequate size to prevent spillages. Provide trays to carry scoops or to hold under scoops in transit. Vacuum the trays regularly
- watch for any poor working methods that may generate dust, for instance banging the scoop vigorously against the container wall when returning unused dye
- you will need to pay particular attention to issues such as cleaning and ventilating the colour store and clearing spillages if dyes are to be carried around in scoops
Emptying dye containers and preparing for final disposal
The design of dye containers and liners can make removing residues and bagging waste difficult to do without creating a dust cloud. Ideally, carry out these tasks under local exhaust ventilation and contact dye suppliers for their advice.
If spills of liquid dye are allowed to dry out, they may release very fine particles of dust. Reduce the likelihood of spillage by using automatic dispensers or carefully choosing transfer containers. Clear up liquid spills straightaway.
Weighing out should always take place under local exhaust ventilation.
Metal scoops can be cleaned by carefully digging them into inert powder, eg Glaubers salt. This cleans the scoops physically without wetting them or creating dust.
You may find the COSHH Essentials sheet RB2 Bag opening and weighing useful. Although aimed at the rubber industry, some of the information is useful when handling dyestuffs.
Transfer of the weighed dyestuff to the next stage
Tipping dry dyestuff into a mixing vessel will create a dust cloud. Weigh the dyestuff into a water soluble bag - the closed bag can be dropped into the mixing vessel and will then dissolve.
Manually mix the weighed dyestuff to a slurry or paste with water before transfer. This could be done, conveniently, under the extraction provided for the weigh scale. Take account of the fact that large containers of dye slurry will be heavy and difficult to handle.
Keep transit containers covered.
Dissolving the dye
Mixing vessels often need additions to be made and this is usually either at chest or shoulder height. Chest height is preferred since there is less chance of a dust cloud being formed in the operator’s breathing zone. Also, manual handling problems will be reduced.
Do not start up high-speed mixers until any dry dye is wetted out and the stirrer blades are covered. To prevent the emission of an aerosol of fine droplets during high-speed mixing, fit vessels with lids. The lids should, preferably, have local exhaust ventilation.
Introducing live steam to an open vessel will create an aerosol. Do not begin any steam heating until the dye solution has been diluted.
You may find some of the information in the COSHH Essentials sheet RB3 Mixing rubber ingredients useful. Although produced for the rubber industry, a lot of the information is useful when handling dyestuffs.
Handling spillages and cleaning
Spillages and cleaning may be a very significant source of dust exposure if not adequately controlled. Brushing up one small spillage can create a greater personal exposure than that received during the rest of the working day. Therefore:
- Prohibit dry methods of brushing and wiping
- Use a vacuum method of cleaning. It may be possible to design an exhaust ventilation system that allows the connection of a suitable vacuum hose for cleaning. Any vacuum cleaner should be suitable for industrial use if it conforms to a standard equivalent to BS 5415-2.2:Supplement No 1:1986 - Type H industrial vacuum cleaners for dusts hazardous to health. A domestic vacuum cleaner will be unsuitable
- As an alternative, use wet cleaning methods
- Employees should wear suitable respiratory protection while handling spillages, cleaning and emptying the vacuum cleaner
Changing filters in the extraction equipment
If this work is carried out in-house, it should proceed according to a written system of work covering the method of removing, handling and disposing of the contaminated filter and the standard of personal protective equipment to be worn. Respiratory protective equipment will be needed. The suppliers of the extraction system should be able to advise you on the method of work.
Benzidine is a carcinogen that can affect the bladder. Dyes that are manufactured using benzidine as a parent compound contain very little benzidine in their finished form. However, it can be regenerated under certain conditions where chemical-reducing agents act on the dye. These conditions can occur during dyehouse processes such as dye stripping or following inhalation or ingestion. Some benzidine-based dyes may themselves be carcinogenic.
In practice, benzidine-based dyes should not be used but they are not specifically prohibited. Within textile finishing less hazardous substitutes have become readily available and there is no practical reason why they can’t be used instead of benzidine-based dyes. In the unlikely event of being able to show sufficient justification for their continued use, you should take the following additional measures:
- Avoid dye-stripping, for instance by re-dyeing a darker shade
- Carry out any unavoidable dye-stripping in enclosed, ventilated vessels
- Prohibit the use of hand cleansers containing reducing agents such as sodium hydrosulphite
Benzidine congener dyes are based on substances chemically similar to benzidine, such as o-tolidine and o-dianisidine, both of which are also carcinogens. Find less hazardous substitutes for them, otherwise take these additional precautions with them.
Reactive dyes have a high degree of wet fastness because the reactive dye molecule fixes itself to natural materials such as cotton, silk, wool or leather by a strong chemical bond. If reactive dyes are inhaled or ingested they can react in the same way in the body. Sometimes this can affect the body’s immune system. Changes to the immune system may mean the next time a person is exposed to the same reactive dye, their body reacts very dramatically, even if the amount of dye involved is very small. If this happens, the person is said to have become sensitised to that dye.
If the symptoms affect the lungs (often affecting the nose and eyes too) this is called respiratory sensitisation. If the symptoms affect the skin, this is called skin sensitisation. Reactive dyes may be respiratory and/or skin sensitisers, although skin sensitisation seems to be rare.
Evidence has shown that a number of reactive dyes have definitely caused respiratory sensitisation in the past. However, there is no validated test procedure for assessing the potential of any individual reactive dye to cause respiratory sensitisation. It is therefore prudent to handle all reactives as if they are respiratory sensitisers. This includes reactives used for dyeing wool.
The hazard to health from reactive dyes is only a concern before their application to the yarn or fabric. There is no known risk to anyone handling or wearing the dyed materials.
Symptoms of respiratory sensitisation
- Eyes: itching, watering eyes or swelling of the eyelids
- Nose: sneezing, itching, running nose or blocked airways
- Chest: symptoms of asthma, such as unusual breathlessness when running or playing sport; coughing, wheezing and chest.
Symptoms of skin sensitisation
- Redness or an irritating rash anywhere on the body, but commonly between the fingers or on the back of the hands and wrists
If someone exposed to reactive dyes displays one or more of these symptoms, you should investigate the possibility of sensitisation. Be aware, though, that the symptoms could be caused by, eg exposure to irritant substances commonly used in dyehouses.
The symptoms may happen immediately on exposure to the particular dye, in which case it will be relatively easy to identify the connection. However, a common pattern is that symptoms are delayed for several hours and are most severe in the evening or during the night. When symptoms are delayed, the affected person might not realise that the ill health is linked with their work - their first indication might come when they have a holiday away from the workplace and realise that the symptoms they have been suffering from have improved or even disappeared.
Five facts to remember about sensitisation
- It is unpredictable. A number of colour-weighers may work with reactive dyes under exactly the same conditions. Some may become sensitised; others may suffer no adverse health effects at all
- Most people who become sensitised to reactive dyes do so during the first two years of exposure but sometimes sensitisation happens years or even decades after starting to work with the dyes
- It is all or nothing: you are either sensitised to a reactive dye or you are not
- It is irreversible - you remain sensitised for life
- People become sensitised to a particular substance and symptoms occur only in response to that substance - if there is no exposure then there will be no symptoms. However, a person who has become sensitised to one reactive dye may then be more likely to suffer adverse reactions to other dyes in the same chemical class.
What happens if exposure continues after a person has become sensitised?
If a person sensitised to a reactive dye continues to be exposed to it, their symptoms are likely to get worse. People who start off by reacting to the dye with a stuffy nose may go on to develop asthma. Asthma attacks are likely to become progressively more severe. Once asthma is established, an attack may be triggered by things other than the reactive dye, such as tobacco smoke or cold air. If this happens, the person may be left with occupational asthma for years after they stop working with the dye.
Some people who develop occupational asthma become so disabled that they cannot work again - not only with dyestuffs but in any job. For some, a slow deterioration in their health caused by the occupational asthma means a shorter life expectancy. In extreme cases, a sudden, severe asthma attack could kill them.
So, it is very important that you take all practicable steps to reduce employees’ exposure to reactive dyes, reducing the risk of anyone becoming sensitised. if someone does become sensitised, it should be recognised as quickly as possible so you can take steps to prevent their symptoms becoming worse.
Making workers aware of the risks
Individuals are in the best position to recognise any deterioration in their own health. However, unless they are informed and regularly reminded of the risks of sensitisation, they may not attach any significance to the early symptoms.
Tell those who work with reactive dyes about:
- what sensitisation is and what can cause it
- what the early symptoms are
- the importance of reporting seemingly minor symptoms at an early stage
- who they should report symptoms to
- the risk of long-term breathing difficulties if exposure to a reactive dye continues after they are sensitised to it
Make sure that your training programme provides:
- guidance on how to handle dyes safely
- information on the arrangements for health surveillance and for reporting suspected symptoms
- the opportunity to ask questions
- opportunities for refresher training
Everyone who may be exposed to reactive dyes should be given training. Most obviously this will be the colour-weighers but it may include other dyehouse workers and laboratory and maintenance staff. Line managers and first aiders also need to understand the risks.
In general, you should handle reactive dyes in the same way as other dyestuffs – see (link to handling dyestuffs safely) above. Also consider the following:
Where technical demands require the use of a reactive dye, choose the least hazardous form of the dyestuff available. The choice of low-dusting dyes such as those in granular, dust-suppressed or liquid form, can be a very important factor in reducing exposure. Remember, however, that dust will be released if liquid spills are allowed to dry or granules become ground down.
The whole process of dispensing powdered and granular forms of reactive dye, not just at the weighing stage, should be carried out under local exhaust ventilation (LEV). If the existing ventilation arrangements in your colour store will not accommodate dispensing dyes, you will need to provide a facility which does. In the interim, people working within the colour store should wear suitable respiratory protective equipment (RPE).
More information about LEV and RPE can be found at the following links:
Health surveillance is appropriate for anyone at risk of being sensitised to reactive dyes. In practice, this means all colour-weighers and any maintenance staff involved in filter changing etc. However, there may be more workers at risk of sensitisation – this will depend on who dissolves the dye and how this is done.
Check that you have ensured the following:
- workers handling hazardous chemicals and dyestuffs are trained and competent, with documented training.
- operators are trained and instructed in correct operating procedures and the purpose and function of controls and safety devices
- special permits are used where employee's need to enter enclosed or confined spaces, eg for cleaning, maintenance, etc
- safe systems of work are used where hazardous substances are pumped into tanks from delivery vehicles, including a competent person overseeing the delivery
- major spillage emergency plan prepared and all employees trained and aware
- colour-coded systems used to help prevent mistakes where hazardous substances are moved in buckets
- there are documented safe procedures/systems of work for sampling and clearing blockages where batching, winding and automatic feeds are used and to protect employees from trapped pockets of superheated water
- there is a formal fault-reporting system to cover leaks of steam or other substances
- emergency showers available and tested weekly