In brief
In the tanneries of Bursa Deri İhtisas ve Karma OSB in Nilüfer, the risks of a chemical plant and a heavy machine shop sit under the same roof. The most serious hazard is hydrogen sulphide, released when sulphide baths meet acid; the smell fading does not mean the gas has gone. Skin protection against chromium salts, constantly wet floors and energy isolation rules for rotating drums are the other main headings of the risk assessment.
Tannery safety at Bursa Deri OSB
Bursa Deri İhtisas ve Karma OSB, in the Badırga area of Nilüfer district, is the organised industrial zone (OIZ) where the city's leather tanning businesses are concentrated; TOSAB Bursa Tekstil Boyahaneleri İhtisas OSB is located in the same area. The zone is known as the place to which the old tanneries in the city centre moved. Tannery safety brings the risks of a chemical plant and a heavy machine shop under one roof: chromium salts and acids, hydrogen sulphide (H₂S) that can be released from sulphide baths, constantly wet floors and drums that rotate tonnes of hides.
Leather processing chemicals change at every stage. The risk assessment should therefore be carried out by process stage, not with a single table for the whole plant:
| Stage | Typical chemicals | Main OHS risk |
|---|---|---|
| Soaking | Water, surfactants, biocides | Biological agents from raw hides, heavy loads, wet floors |
| Liming (unhairing) | Sodium sulphide, sodium hydrosulphide, lime | Caustic burns; H₂S if in contact with acid |
| Deliming and bating | Ammonium salts, enzymes | H₂S and ammonia as pH falls, sensitisation to enzyme dust |
| Pickling | Salt, formic and sulphuric acid | Acid burns, H₂S from residual sulphide |
| Chrome tanning | Basic chromium sulphate | Skin contact, dust, allergic dermatitis |
| Dyeing and fatliquoring | Dyes, oils, synthetic tannins | Powder dyes, skin contact |
| Finishing | Solvent- and water-based coatings | Solvent vapour, fire |
| Effluent channels and treatment | Sulphide-bearing and acidic streams | H₂S build-up, confined space, asphyxiation |
Sulphide and H₂S: the tannery's most insidious hazard
The sulphide used for unhairing turns into hydrogen sulphide gas when the environment is acidic. H₂S is to be expected in three places in a tannery:
- In deliming and pickling drums: as the pH falls, the sulphide remaining in the hide is released as gas. Concentration is highest the moment the drum door is opened.
- In channels, manholes and equalisation tanks: gas builds up where sulphide-bearing and acidic effluent streams mix. These points count as confined spaces.
- In storage and dosing: storing sodium sulphide close to acids or carrying them in the same container leads to uncontrolled gas release.
At low concentrations H₂S makes itself known by a rotten egg smell. As the concentration rises, the sense of smell is paralysed; a worker may interpret the smell fading as the gas having gone. That is why in a tannery the gas is monitored by detectors, not noses.
Annex 1 of the Regulation on Health and Safety Measures for Work with Chemical Substances sets the 8-hour limit value for H₂S at 5 ppm and the 15-minute short-term limit value at 10 ppm.
Measures at source come before detectors:
- Collect sulphide-bearing and acidic effluent streams in separate channels; make the mixing point controlled and ventilated.
- Run drum ventilation or local exhaust during deliming; write the waiting time before opening the door into the work instruction.
- Store sodium sulphide separately from acids, in a dry and locked area. For segregating incompatible chemicals, see our article on compatible storage of chemicals.
- Dose chemicals with closed systems wherever possible; minimise manual transfer with open buckets.
Chromium in leather tanning: skin, eyes and breathing
The basic chromium sulphate widely used in tanning is trivalent chromium. Hexavalent chromium is more toxic and is classified as a carcinogen; it can form in the process or in waste under certain conditions. If a chemical containing hexavalent chromium is used on site, the provisions of the regulation on carcinogenic substances also apply in addition to the Chemical Substances Regulation.
Three effects stand out when working with chromium salts:
- Skin: Chromium is a known cause of allergic contact dermatitis. Handling wet hides with bare hands, liquid getting inside gloves and long periods of wet work increase the risk.
- Eyes: Eye irritation occurs when powdered chromium salt is poured or a bath splashes.
- Breathing: Powder chemicals emptied by hand from bags into drums are inhaled.
The order of measures is clear: feed powder chemicals through closed dosing or an emptying point with extraction; reduce open bag emptying. Provide workers with chemical-resistant gloves reaching beyond the wrist, a waterproof apron and eye protection. For glove selection, see our article on choosing work gloves, and for the early signs of dermatitis, occupational dermatitis.
Wet floors, heavy hides and drums
In a tannery the floor never dries: water, lime, oil and hide waste combine on the same surface. Slips and falls are therefore common. Sloped floors and drainage grates, anti-slip floor coatings, sound channel covers and waterproof safety footwear with high slip resistance are the basic measures. For footwear selection, see our article on safety footwear classes.
Wet hides are heavy, and carrying them by hand loads the back. Raw hides and intermediate products should be moved by trolley or pallet; the drum loading height should be arranged to reduce manual lifting.
The drum is the heart of the tannery process. Large rotating drums turn hides in chemical baths for hours, and the most serious accidents happen at the drum:
| Machine or area | Hazard | Measure |
|---|---|---|
| Drum door | Unexpected rotation of the drum during loading and unloading | Energy isolation and lockout, a brake or pin that fixes the drum |
| Drum surroundings | Being caught by the rotating drum or drive gear | Barrier preventing access during operation, gear and belt guards |
| Dosing opening | Chemical splash, gas release | Closed dosing, face shield, extraction |
| Fleshing and shaving machines | Hands caught in rollers and blades | Fixed guard, two-hand control, emergency stop |
| Stretching and drying | Hot surfaces, entrapment | Guard, hot surface sign |
During drum loading or unloading, the drum control must be locked out and the key must stay with the person doing the work. For the steps, see our article on the LOTO procedure, and for guard types, machine guards.
Risk assessment and health surveillance plan
In a tannery, risk assessment and health surveillance feed each other. The order we recommend is:
- Draw up a chemical inventory. The safety data sheet, the stage where it is used and the quantity of each chemical are listed. For the method, see our article on the chemical inventory.
- Assess by stage. The table above is a starting point; each drum, channel and machine is assessed as a separate row.
- Plan workplace measurements. We plan measurements of H₂S, ammonia, chromium compounds, solvent vapour and noise with authorised laboratories and enter the results in the risk assessment.
- Set up health surveillance according to exposure. The pre-employment examination asks about skin and allergy history, respiratory complaints and hearing. In periodic examinations the skin of the hands and forearms is examined; the workplace physician decides which tests are carried out and how often, based on exposure. We plan the tests with authorised healthcare providers.
- Link emergencies to scenarios. Separate scenarios are prepared for an H₂S alarm, chemical splashes and spills; an emergency shower and eyewash are placed in the drum area. For spill response, see our article on responding to chemical leaks.
- Deliver training by stage. Job-specific risk topics are delivered face to face in hazardous and very hazardous workplaces; the training content for a drum operator and a finishing worker should not be the same.
Bursa Sistemer OSGB carries out risk assessment by process stage in tanneries and chemical businesses in Nilüfer and the surrounding area, and builds the health surveillance programme on the findings of this assessment. For other risks in the sector, see our chemicals and plastics page.
Frequently Asked Questions
How often should H₂S be measured in a tannery?
For continuous monitoring, fixed detectors should be installed at drum heads and around channels and tanks. The frequency of personal exposure measurements is set by the risk assessment; measurements are repeated when the process, chemicals or ventilation change. Measurements should be carried out by authorised laboratories.
Is chrome tanning carcinogenic?
The basic chromium sulphate used in tanning is trivalent chromium and is not classified as a carcinogen, but it can cause allergic dermatitis. Hexavalent chromium, however, is carcinogenic. Check the valency of the chemical used on its safety data sheet.
Is it really necessary to isolate energy during drum loading?
Yes. During loading and unloading, the worker's body enters the drum's range of movement. The drum control must be locked out and, where possible, the drum fixed mechanically. No exception is made for short jobs either.
What examinations are carried out for tannery workers?
In pre-employment and periodic examinations, skin, respiratory health and hearing come first. The workplace physician decides, based on the level of exposure, whether tests such as a chest X-ray, lung function test, hearing test or biological monitoring are needed and how often.
A risk assessment that identifies and scores hazards on site, links each measure to an owner and a date, and has a clear renewal schedule.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.