Sprinklers and watermist: they are not the same!

Dale Kinnersley, FPA Principal Consultant, cross-examines the differences between sprinkler and watermist systems.

This article looks at the comparison of sprinkler systems and watermist systems for general building fixed fire suppression/protection using a sealed-bulb wet pipe system. Watermist suppression for other applications are not covered within this article.

When it comes to the correct selection of fixed fire-fighting suppression systems, there are many external influences that can affect the correct specification of fire suppression for the protection against fire of many buildings. By far the two biggest influences are cost and space, when the decision should be based on hazard, risk, effectiveness, longevity of water supply, fire strategy, third-party approvals, standards, research & testing, proven track records, and insurability.

The two common fixed fire systems specified today in building construction are sprinkler systems and watermist systems, each having their own place within the industry and both using different methods and technologies for suppression.

Sprinkler systems have been around for hundreds of years – going as far back as the 18th century. In 1812, the first known UK sprinkler system was installed into Drury Lane Theatre, London. Henry S Parmelee developed the first automatic sprinkler head in 1874, and the first recognised sprinkler rules were published in 1887 by John Wormald of the Mutual Fire Insurance Corporation Ltd Manchester. Sprinkler systems fight fires by cooling, using water as the medium discharged directly over the seat of the fire, which also provides wetting of the surrounding combustibles to prevent fire spread and controlling the fire until final extinguishment is undertaken by the local fire and rescue service. Depending on the hazard classification of the building, water supplies range from 30 minutes up to 90 minutes.

Sprinkler systems have a proven track record for reliability and effectiveness across all premises when properly maintained and installed – fire sprinklers are by far the most efficient and effective fire safety devices known. Over the past 130 years they have had a better than 99% success rate in controlling fires around the world. The installation of fire sprinklers will virtually eliminate fire deaths, reduce injuries by at least 80%, reduce property damage by 90% and substantially reduce damage to the environment from fire (source: BAFSA).

Watermist systems are a relatively new technology that has been developed over the past 30 years, starting life offshore in the enclosed engine rooms of ships. More recently, watermist is now seen as a viable alternative to sprinkler systems for the protection of occupants of buildings and for providing dedicated protection to certain types of equipment. Despite a similarity to sprinkler systems, watermist is different in many ways, from its firefighting technology to the equipment, building requirements, approvals, and requirements of the manufacturer’s DIOM (Design, Installation, Operation, and Maintenance manual) and their bespoke components. Watermist is designed to provide fine droplets of water of less than 1000μm (1mm) to control, suppress, or extinguish a fire by providing thermodynamic cooling through evaporation and oxygen reduction through steam displacement. However, this is not easily achievable as certain environments within a building will affect the watermist from developing and therefore controlling a fire. How long the fire has been burning, the size of the fire, ventilation effects, and watermist delivery density will all effect the performance of the system and its ability to control a fire.

As watermist is a relatively new technology, it cannot boast the same historical efficacy as sprinkler systems and does not have the historic data to prove its effectiveness and success.


Within the UK there are a handful of standards that can be used for the sprinkler protection of buildings:

  • BS EN 12845:2015+A1:2019 – Commercial and Industrial Sprinkler Systems
  • LPC Rules for Automatic Sprinkler Installations 2015 incorporating BS EN 12845
  • BS 9251:2021 – Residential Sprinkler Systems
  • BS EN 16925:2018 – Residential Sprinkler Systems
  • N.F.P.A. 13 (American Standard)
  • FM Data Sheets (American Standard for FM Global Insurance Company)

The most common standards adopted are BS 9251, BS EN 12845, and the LPC Rules, however, these documents have different purposes. A BS reference is to a British Standard, EN refers to a European Norm standard, which is a harmonised European standard adopted by the British Standards Institute. Reference to either a BS or BS EN is a minimum standard for the protection of life as mandated by UK government. It is a standard that allows 
occupants to escape before building collapse. If all occupants escape safely, the building burns to the ground, and the business is lost, this is a successful outcome as seen in the eyes of the government for life safety.

The LPC Rules are property and business continuity protection standards and are split into three parts. Part 1 is the BS EN 12845 standard. Part 2 are the LPC Technical Bulletins, known as TBs, which are additional requirements for the protection of the building and business continuity. These are written and detailed by RISCAuthority, sprinkler insurance experts and likeminded stakeholders such as BAFSA and the LPCB. Part 3 is additional fire risk control guidance linked to sprinkler systems. Altogether, the LPC Rules represent the best sprinkler protection standards to cover both life and property.

For watermist, there are currently three main standards used in the UK:

  • BS 8458 – Residential and domestic watermist standard
  • BS 8489-1:2016 – Industrial and commercial watermist standards
  • BS EN 14972-1:2020 – Watermist systems

These standards are minimum life-safety standards to allow occupants to escape before building collapse and do not cover property protection or business continuity.

BS EN 14972-1 is the design, installation, inspection, and maintenance manual for watermist systems produced by European committee at CEN. CEN is currently producing EN 14972 as a suite of documents, with parts 2 to 17 as test protocols that accompany part 1. Some of this has already been published by CEN, but has not yet been adopted by the British Standards Institute at the time of writing this article. Due diligence is required to ensure that when using the new European standard EN 14972, the relative test protocol document has been published which covers the criteria for which the system is designed to protect.

Third-party approvals

A major difference between the two suppression systems comes in third-party approval. Sprinkler contractors, companies, installers, project staff, and designers need to demonstrate they are third-party approved and have the correct certification, training, competence, and industry qualifications. All sprinkler equipment must be third-party approved, and most of the sprinkler equipment is fully interchangeable. Constant periodic auditing of sprinkler companies is undertaken to ensure that they meet the requirements for the schemes that they are accredited to (LPCB/FIRAS/IFC), and that they have a recognised (UKAS) ISO9000 Quality Assurance system in place.

As a new technology, watermist does not currently have the same third-party level of engagement for either the companies or the components. There are a limited number of companies signed up to third-party schemes, and very few nozzles that have approval and are listed with third-party recognition. It is also widely recognised that watermist systems and their components are bespoke to each manufacturer. This therefore requires compliance with their DIOM, and there is a very low level (if any) of interchangeability of components.


The insurability of a building depends on the protection scheme for said building by using standards which provide additional resilience enable insurance companies to adjust premiums based on these standards, the building, and the business. When it comes to insurance approval for suppression systems, a sprinkler system fully designed and installed to the LPC rules is widely acknowledged for property protection and business resilience. A suppression system designed and installed to BS or BS EN (life safety) is not typically recognised by insurers, and as such buildings containing life safety systems are not considered protected. It has been known that insurance premiums have been loaded rather than discounted for these system types.

Insurers have repeatedly expressed concerns over watermist and the comparison to sprinkler systems. They have confirmed that there is not an equivalency between the two systems based on the considerations relating to standards, third-party schemes/certification, and lack of historical evidence of efficacy.

For insurers to consider a watermist system applicable as an alternative to sprinklers, three questionnaires written by RISCAuthority are offered to specifiers, watermist companies, and manufacturers to complete. The questionnaires ask specific details to be made available, query test protocols, and require details of the certification of the system for use in the proposed environment. Failure to fully complete any of these questionnaires serves as a red flag warning to the insurers and questions the ability of the proposed system to perform its intended task. These questionnaires (IQ1, IQ2, and IQ3) are available through the RISCAuthority website. Additionally, some insurance companies have their own system to review the capabilities of proposed suppression systems prior to accepting applications for property protection and business resilience.


Sprinklers or watermist? There are considerations that need to be addressed when choosing one over the other. Both systems have their benefits, both systems have nationally recognised standards, both systems have third-party recognition, albeit one is widely acknowledged, and the other is lacking in evidence. For a fixed suppression system to be recognised by insurance companies, a fully compliant sprinkler system to the LPC rules is almost guaranteed, other systems, including residential sprinklers systems and watermist, however may not be recognised.

Watermist as a suppression system is still an emerging and promising technology that utilises different characteristics to sprinkler systems which make it effective and attractive. Due diligence is required when considering watermist over sprinklers. Experience confirms that in terms of cost difference between both technologies, watermist is slightly more expensive. Caution needs to be exercised by authorities having jurisdiction when recommending or approving watermist systems. Evaluation of compliance to the standards, installers competency using listed and approved equipment, confirmation that the system can perform as required when needed, and recognition by insurers should be sought. Watermist can be the best option for many applications, but not all. It is imperative to fully understand all performance factors pertinent to meeting the design intent and fire strategy of the building, and then assessing whether or not it is the best option.

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Dale Kinnersley is Principal Consultant at the FPA.