Professional Pest Controller Magazine Issue 107

31 May 2022

Accreditation standards in focus: Pest risk assessments

Technical | PPC107 June 2022

Food Accreditation Standards can be a minefield, with different specifiers needing different things from you.

In this new series, Grahame Turner from BPCA Consultant member company PestAcuity, will turn his attention to different aspects of common standards. First up are pest risk assessments – what are they, how do you do one and why does a site need one in the first place?

Pest risk assessments British Pest Control Association PPC107

Increasingly, food safety standards require that the specification of the pest control contract for a site is based upon a ‘pest risk assessment’ (PRA).

The assessment needs to evaluate the business for the potential for intrusion or infestation by any animals that might affect the safety or quality of the products being manufactured or handled at the site.

A PRA needs to be completed at least annually and reassessed if there has been a significant infestation or building modification.

The key expected outcomes from the PRA are for guidance on which pests need to be monitored for and on how frequently the technician and biologist inspections should be undertaken.

The frequency of ‘routine’ inspections would typically be selected from 8, 12, 26 or 52 per annum.

But if the site has seasonal variation, then it might differ from this by having intensive visits during part of the year and less frequent visits at other times. The frequency of biologist visits will usually be 1, 2, 4, or 12 per annum.

The PRA needs first to consider which pest types might infest a site.

Rats, mice, flies and cockroaches are always a potential threat; but whether or not any stored product insects need to be monitored for will differ for different products, and whether proactive external wasp controls need to be implemented will also be product/ingredient specific.

Once the species to be included in the contract specification have been considered and decided, the PRA then needs to determine how likely each of them is to infest.

And the risk of each will depend on a wide variety of factors, such as neighbours, building fabric type and condition, building configuration, door policy, waste control, raw materials suppliers, site cleanliness, complexity and cleanability of equipment, etc. 

Infestation history is also an important detail to be considered as, if nothing has subsequently changed, it can be a good indicator of future re-infestation potential.

A PRA needs to be completed at least annually and reassessed if there has been a significant infestation or building modification.

Grahame Turner, PestAcuity

OK, so you have checked the site and the practices and noted a series of factors that could have a positive or negative impact on different pest infestation potential.

But what do you do then to help you decide the pest risk? How can you score it? And how can you document and present it?

Here are three techniques:

Simple subjective assessment

For a subjective view of risk based on your observations, you could record as you inspect the site a list of positive and negative features. 

You could then form a view as to which are significant risks when combined (eg for rats it could be ‘infested neighbour’ plus ‘poor proofing’); and which attributes might offset which hazards (eg with rats a 3m gravel band around a building might help to counteract grounds with potential rat harbourage). 

Or you could give a subjective risk score to each of say low risk, medium risk, high risk. Then you could judge the overall risk and recommend visit frequency accordingly eg:

  1. Low risk – 8 visits per annum
  2. Medium risk – 12 vpa
  3. High risk – 24 vpa.

Risk matrix

The overall likelihood (risk) of an infestation will vary depending on a series of local factors. Those factors can be assigned a risk number based on the likelihood that they would lead to an infestation. 

Showing your observations and calculations in tabular form can clearly illustrate to the customer what risk you have assigned to each of your observations. 

For example, for the risk of internal rat infestation, your table might look something like table 1 (below).

And for each different level of controlled risk, you might have a pre-assigned number of vpa for checking external rat boxes, eg.

Controlled risk vpa
5 52
4 26
3 12
2 8
1 4

So, for the above scenario the recommended number of vpa to inspect external rat boxes would be 12 (ie monthly). 

Table 1

Risk factor     Risk     Worst risk   Controls (since previous rat infestations)     Controlled risk
Neighbouring farmland  3 5 Building well-proofed
3m gravel band around building
Good door policy
Pair of rat break-back traps placed internally each side of Goods In and Despatch doors
Neighbouring railway 2
Accumulation of storage in grounds 1
Dense vegetation in grounds 1
Poor waste management 5
Product highly attractive to rats 3
Three internal rat infestations in last two years 5

An alternative scenario might look like table 2 (below). Or it could be any number of other combinations of risk components and controls.

The severity (hazard) of an internal rat infestation would be classed as high (ie severity 5) because they could not only affect food safety, but also spread potentially fatal diseases to staff.

But in my view, we don’t need to include hazard severity for each pest type in the table, as that would just complicate it for no additional benefit. The hazard can just be taken into account in the risk scoring.  

You might like to make it clear to the customer in your PRA document what they can do to help reduce the risk.

So, you might like to include a full list of all the factors you consider when compiling your PRA, along with the associated risk score.

Risk factor     Risk     Worst risk   Controls (since previous rat infestations)     Controlled risk
Poor proofing (very old buildings) 4 4 Good waste management
No previous rat infestations
Good door policy
Vigilant staff
Packaging manufacturer (not attractive for rats)
Untidy fast food restaurant next door 4
Urban area 3
Litter accumulations on pavements 2

Decision tree

To simplify the process, you could use a ‘decision tree’. So, for example, with external rat monitoring, you could have a table along the lines of the condensed one below. 

As you do your survey, you tick all that apply. The lowest tick would then tell you what the recommendation to the customer should be. In your working tick list, each factor would also have space for comments to record some supporting information.

Factors affecting external rat visit frequency Tick Routine inspection frequency
Minimum frequency   8 vpa
High potential for infestation from neighbour   12 vpa
Grounds provide favourable habitat for rats  
Fabric or management of the building allows rodent entry  
No2 + no4 or no3 + no4 above applies   24 vpa
Food waste management issues in grounds  
Two or more separate internal rat infestations in the last 12 months  

The assessment needs to be repeated for each pest type (internal rodents, crawling insects, flying insects etc), taking into account relevant risk factors for each pest type.

And the risk factors might vary depending on the product eg ‘high-risk’ foods might demand a greater frequency of visits than dried foods. 

You might end up with different visit numbers for different pest types eg fortnightly visits for SPI, but monthly for rodents; or different numbers of visits for different internal parts of the same site.

And with the PRAs being regularly repeated, the infestation risks and the frequency of visits can change over time.

Of course, it’s the client who has the ultimate say in pests monitored and the number of visits, because it is them who are paying for it. So, they are at liberty to specify either fewer or more visits than the PRA outcome.

Deciding on fewer visits might negatively impact audit scores from their customers or from accrediting bodies, so they would be wise to document their justification for it.

The rationale behind pest risk assessments is that instead of the site just selecting pests monitored and frequency of visits based on cost, the ongoing contract specification is determined by intelligent reasoning, which is a better scenario for both contractor and client.

Grahame Turner, PestAcuity

In addition to the PRA, some standards have individual requirements that can affect visit frequency. 

Three supermarkets specify that their suppliers have a minimum of eight routine and four biologist vpa; one standard requires that all external monitors are inspected at least monthly; and one supermarket requires that where rodent break-back traps are used for internal monitoring, these need to be inspected weekly. 

In my experience, this hampers proactive pest management, as instead of using traps in place permanently to catch any rodents that do enter a premises, pest companies use non-toxic bait for all internal monitoring.

So, infestations can get well-established between routine visits. This can be the case where COSHH assessments, CRRU considerations, other standards, or high risk of wood mice intrusion, rules out permanent toxic baiting.

The rationale behind pest risk assessments is that instead of the site just selecting pests monitored and frequency of visits based on cost, the ongoing contract specification is determined by intelligent reasoning, which is a better scenario for both contractor and client.

There is no prescribed way to carry out a PRA (yet), so you are free to decide your own system. 

Standards regularly change – always make sure you are working from the current documents.

Need help?

Grahame Turner of PestAcuity Ltd is available for advice on pest risk assessments and food industry pest control.

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