Fireworks are, basically, small explosives using chemical reactions to generate light and noise. Naturally, some of them can be quite loud. How loud they are, however, depends on a number of factors.

In the UK, fireworks fall into four categories roughly based on explosive power, and the public cannot buy the bigger and louder fireworks. Some fireworks are made for their display properties, - the oooh and aaah factor - while others are designed to boom and bang.

Handling fireworks safely has been well covered in public health campaigns, but less emphasis has been placed on the risks to hearing health from loud fireworks. Let’s take a look at some of the science behind the sound.

What makes fireworks loud?

The chemical reactions inside a lit firework lead to a build-up of heat and gas. These cause an explosion that creates a blast wave because of the release of a large amount of energy in a small volume. This wave creates an area of very high pressure, causing compressed air particles to travel faster than the speed of sound – which creates the bang.

Loudness is defined as the intensity of the sound, and the power of a sound wave is proportional to the pressure squared. So the bigger the explosion, the higher the pressure and the louder the sound. Atmospheric conditions can also affect how the sound wave travels, and the same fireworks can vary in loudness from one night to the next.

How is sound measured?

Decibels (dB) are used to measure how loud a particular sound is. Experts agree that hearing loss can occur at just 85dB, depending on the length of exposure.

Sound level Example Safe exposure limit
85dB Kitchen blender 8 hours
88dB Forklift truck 4 hours
91dB Tube train 2 hours
94dB Lawn mower 1 hour
97dB Industrial fire alarm 30 minutes
100dB Hand held drill 15 minutes
103dB MP3 player max vol 7.5 minutes
106dB Motorbike 3.75 minutes
109dB Crying baby 112 seconds
112dB Live rock band 66 seconds

For full details on sound levels see our leaflet on Noise and the ear or visit our tinnitus prevention campaign website, Plug'em.

How loud are fireworks?

Fireworks in commercial displays are often over 150dB and sometimes as much as 175dB. These can only be sold to fireworks professionals, as the public cannot buy fireworks of louder than 120dB at 15 metres.

However, as commercial fireworks can reach much higher into the sky than those used at home, their sound can be weaker to observers on the ground. Fireworks sold to the public usually explode much closer to the ground and although they have a lower maximum decibel level, they can actually sound louder.

Hearing safety around fireworks

As the sound intensity to which you are exposed varies according to how far away you are, it makes sense not only from a physical injury point of view to stand as far back from a firework as you can, but from a hearing health viewpoint too.

Make sure any children are as positioned safely too. The World Health Organization recommends that children should be exposed to no more than 120dB, which may be difficult to achieve in a small garden, and so hearing protection is strongly recommended. Very small children are highly sensitive to the physical effects of sound pressure so again, over-ear hearing protection should be used, or consider not letting off loud fireworks.

The length of time you are exposed to loud noise also matters. The safe limit is regarded as 85dB for no more than 8 hours and some experts suggest 80dB as the upper limit. The safe exposure time is cut in half for each three decibel increase over 85dB. At 120dB, the safe exposure limit is less than 10 seconds, so setting off a few fireworks over the course of an evening in your garden could indeed cause hearing damage or trigger tinnitus. Hearing protection will reduce your exposure to loud noise, and still enable you to have a fun and exciting firework display. Save me a sparkler!

Photo by Vernon Raineil Cenzon on Unsplash