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Fig. 1: Most Indian shop floors sit somewhere between 85 and 100 dBA. The law has something specific to say about every one of those numbers.
The quick answer
The occupational noise limits in India come from the Schedule to the Model Factories Rules made under the Factories Act, 1948. The ceiling is 90 dBA for an eight hour shift. Every 5 dBA above that halves the permitted time, no continuous exposure above 115 dBA is allowed at all, and impulse noise is capped at 140 dB peak. A separate law, the Noise Pollution Rules, 2000, governs what your factory may emit at its boundary. They are different limits for different purposes and people confuse them constantly.
01 /Where the occupational noise limits in India come from
Ask ten plant managers what the noise limit is and you will get 85, 90 and "I think there is a rule" in roughly equal measure. The answer is in a specific place.
- The parent law is the Factories Act, 1948. It obliges the occupier to protect workers' health, but it does not print a decibel figure.
- The number lives in the Rules. The Schedule on noise in the Model Factories Rules sets the permissible exposure table. States adopt this into their own Factories Rules, so the Schedule number varies by state even though the figures are the same.
- Enforcement sits with the state factory inspectorate, not the pollution control board. Different inspector, different law, different limit.
If you are looking it up for a compliance file, ask for your own state's Factories Rules rather than the model set. The content matches, the numbering will not.
02 /The exposure table you actually need
This is the table. Time is the total for a working day, and the level is measured in dBA.
| Total daily exposure | Permitted sound level |
|---|---|
| 8 hours | 90 dBA |
| 6 hours | 92 dBA |
| 4 hours | 95 dBA |
| 3 hours | 97 dBA |
| 2 hours | 100 dBA |
| 1½ hours | 102 dBA |
| 1 hour | 105 dBA |
| ¾ hour | 107 dBA |
| ½ hour | 110 dBA |
| ¼ hour | 115 dBA |
No exposure in excess of 115 dBA is permitted, for any length of time.
Impulse and impact noise, the press shop and the drop hammer, is handled separately by peak level and count:
| Peak sound pressure level | Permitted impulses per day |
|---|---|
| 140 dB | 100 |
| 135 dB | 315 |
| 130 dB | 1,000 |
| 125 dB | 3,160 |
| 120 dB | 10,000 |
Nothing above 140 dB peak is permitted at all.
03 /Two different laws, two different limits
The boundary limit is a separate instrument, and this is where most confusion starts. The Noise Pollution (Regulation and Control) Rules, 2000 set ambient limits by zone, measured in dB(A) Leq:
| Zone | Day, 6 am to 10 pm | Night, 10 pm to 6 am |
|---|---|---|
| Industrial | 75 | 70 |
| Commercial | 65 | 55 |
| Residential | 55 | 45 |
| Silence zone | 50 | 40 |
A silence zone is an area of not less than 100 metres around hospitals, educational institutions and courts.
So a plant can be entirely legal inside and still in breach outside:
- Inside the shed, 88 dBA for eight hours is within the Factories Rules limit.
- At the boundary, the same plant must sit at or below 75 dB(A) Leq during the day if it is in an industrial zone.
- If a residential colony has grown up next door, the applicable zone at that receiver becomes the argument, and the night figure of 45 is where most complaints are won or lost.
04 /What 90 dBA means in practice
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Fig. 2: A meter tells you the level. It does not tell you the dose, which is the level and the time together.
Three things worth understanding before you spend anything:
- India uses a 5 dB exchange rate. The permitted time halves for every 5 dBA. Several other countries halve it every 3 dBA, which is stricter and closer to how sound energy actually adds up. The practical effect is that the Indian table is more permissive at the top end than it looks.
- 90 dBA is a limit, not a target. A great deal of international occupational practice treats 85 dBA as the level at which you start acting, well before anything is technically breached. Sitting at 89 dBA and calling it compliant is legally defensible and not a good outcome for the person standing there.
- Dose is what matters, not the peak reading. A single walk-around reading proves very little. What counts is the level a specific worker actually receives across the whole shift, which is why personal dosimetry beats a clipboard and a meter.
Noise induced hearing loss is permanent and painless while it is happening, which is exactly why it gets ignored. The World Health Organization's World Report on Hearing places occupational noise among the preventable causes of hearing loss worldwide. If people on your floor are shouting to be heard at arm's length, you do not need a meter to know you have a problem, though you will need one to prove it. Audiometric testing and any clinical judgement belong with an occupational health professional, not with an acoustic consultant.
05 /Fix it in the right order
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Fig. 3: An enclosure around the source. Expensive on the quotation, cheap against a hearing loss claim.
The hierarchy is not a formality. Anything lower down the list only works when everything above it has been tried.
- Eliminate or substitute. A quieter machine, a different process, a nylon component instead of a steel one. The cheapest decibels are the ones bought at procurement.
- Enclose the source. A lined enclosure around a compressor, blower or press attacks the problem where it is smallest and most contained.
- Interrupt the path. Barriers, lagged ducting, vibration isolators under the machine feet so the structure stops radiating.
- Treat the room. Absorption on the roof deck and upper walls cuts the reverberant build up. It will not fix the operator standing beside the press, and it will noticeably reduce the level everywhere else.
- Separate the people. An acoustic control cabin or rest area gives the shift somewhere to recover, which shortens their daily dose.
- Then, and only then, hearing protection. PPE is the last line, not the plan.
06 /What tends to work on an Indian shop floor
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Fig. 4: A sealed supervisor cabin. The cheapest way to take hours off somebody's daily dose without touching the machines.
- Start with the top three sources. In most plants a very small number of machines produce most of the exposure. Find them before you buy anything.
- Enclose the compressor and the DG set first. They run constantly, they are usually in a hard walled room, and they are the easiest wins available.
- Fix the roof deck. A profiled metal roof over a hard floor is a reverberation chamber. Absorption up there lowers the general level across the whole shed.
- Seal the cabins you already have. Most supervisor cabins fail on the door and the cable entries, not the walls. A drop seal and some acoustic sealant is an afternoon of work.
- Rotate people, not just protectors. Job rotation reduces the individual dose without a single rupee of capital spend, and the exposure table is written in hours precisely so you can use it that way.
- Keep the records. Survey results, dosimetry, audiometry dates and what you changed. In a dispute, the documentation is the defence.
If your problem is the office block rather than the shed, the same logic applies at lower levels, and our guide to office soundproofing for Indian workplaces covers it. If you are specifying enclosures or barrier materials and want to know what to demand from a supplier, the questions to ask an acoustic supplier apply here too, particularly the insistence on a real test report.
07 /Frequently asked questions
What are the occupational noise limits in India?
The Schedule on noise in the Model Factories Rules, made under the Factories Act, 1948, permits 90 dBA for an eight hour day. The permitted time halves for every 5 dBA above that, giving 95 dBA for four hours, 100 dBA for two hours and 105 dBA for one hour. No continuous exposure above 115 dBA is permitted, and impulse noise is capped at 140 dB peak sound pressure level.
Is the factory limit the same as the pollution control board limit?
No, and this is the most common mix up. The Factories Rules limit protects the worker inside and is expressed as a level against a duration. The Noise Pollution (Regulation and Control) Rules, 2000 protect the neighbourhood and set boundary limits by zone: 75 dB(A) Leq daytime for an industrial area, down to 45 at night in a residential area. A plant can comply with one and breach the other.
Is 85 dBA safe because the legal limit is 90?
Legal and safe are not the same word. Much international occupational practice treats 85 dBA as the point at which action begins, and India's 5 dB exchange rate is more permissive than the 3 dB rate used in several other countries. Treat 90 dBA as the boundary of the law, not as a target, and act well before you reach it.
Are ear defenders enough on their own?
They are the last control in the hierarchy, not the first. Real world attenuation is usually well below the laboratory rating because of fit, hair, spectacles and the fact that people remove them to speak. Use them, and use them alongside enclosures, barriers, room absorption and job rotation rather than in place of them.
Himanshu writes about measurement, materials and the physical effects of noise on the people exposed to it. He has a low tolerance for performance figures quoted without a test standard behind them.
