Variation against the fire alarm code BS5839

When designing fire alarm systems, there are occasions, when the fire alarm designer will deviate away from the standard. The recommendations are primarily based on recognized good practice in the design,  installation, commissioning and maintenance of fire detection and fire alarm system. Accordingly, they are
likely to be suitable for the majority of normal applications.
There will, however, be applications in which the recommendations are unsuitable and would lead to fire alarm systems that would be unnecessarily expensive, incorporating measures that could not be regarded as  cost-effective, or that could be difficult to install. In extreme cases, the recommendations might even be
inadequate to provide the appropriate level of protection.
In these circumstances, variations from the recommendations may be necessary, even though, in general, the user, purchaser, enforcing authority or insurer requires quite strict compliance with the standard.
Variations were described as “deviations” in the previous version of this part of BS 5839. This term is now
deprecated, since it implied shortcomings or errors in design, whereas, in reality, the term referred to aspects
of design that were appropriate and intentional, albeit not compliant with one or more recommendations of
the standard.
This does not, however, imply that the designer or installer has freedom to ignore the recommendations of
this standard under circumstances in which a user, purchaser, enforcing authority or insurer seeks
compliance with it. Variations always need to be the subject of specific agreement amongst all interested
parties and need to be clearly identified in all relevant fire alarm system documentation.
Some variations can arise from a fire risk assessment, in which it is determined, for example, that an area of the building may be unprotected by automatic fire alarm system, albeit that, in the Category of fire alarm  otherwise deemed necessary, protection is recommended in this standard. Other variations may be based on
the engineering judgement of a competent person, who might, for example, consider that the extent of protection disabled in the event of a single cable fault can slightly exceed the limitations recommended in  this standard, without any significant decrease in the integrity of the fire alarm.
It also needs to be borne in mind that, while it is necessary for certain limitations or performance levels  recommended in this standard to be quantified, so that the relevant recommendations are expressed
numerically, the values quoted are often arbitrary. The values are often based on well-established and
proven custom and practice, or on the judgement of experts. While they are, therefore, generally applicable,
rigid adherence to them might not be appropriate in every case, nor is it the case that minor variations need necessarily have any significant effect. Any deviations away from the standards should be after a fire risk assessment has been conducted.