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Tree Risk- What's the Likelihood of Failure?


Rodbaston, Staffordshire


Frank Rinn and David Evans

7 hours

Places Available


Exc. VAT Inc. VAT

Course Objectives:

This indoor and outdoor seminar shines a spotlight on how you can boost your ability to make credible, consistent, and calibrated likelihood of failure decisions.  Set in the context of the most recent developments in tree risk-benefit assessment, the morning presentations will outline the foundations on which the practical, hands-on, afternoon field sessions are built.  A thought-provoking day will provide you with essential knowledge in biomechanics. The ifs and buts of likelihood of failure decision-making.  And an unmissable opportunity to calibrate your likelihood of failure estimates with other arborists.

  • Provide a solid grounding in the significance of wind load, stem geometry, and wood strength on the likelihood of failure
  • Recognise the difference between basic and residual safety factors
  • Appreciate when strength-loss formulae, such as t/R ratios, are relevant and irrelevant
  • Understand how much decay is too much, and why location of decay can be more important than extent
  • Provide an overview of the strengths and limitations of equipment including the resistograph and Arbotom.
  • To understand what a Static Load Test is and what it measures
  • Highlight the importance of ‘Goldilocks’ ranges – benchmarking, uncertainty, and confidence for likelihood of failure decisions
  • Recognise tree defects/features and decide when more information is required to make a credible risk assessment decision
  • Discuss the component parts of defect likelihood of failure decisions
  • Overview the advantages and disadvantages of quantitative (numbers) and qualitative (words) tree risk assessments
  • Introduce the VALID* Tree Risk-Benefit Assessment system
  • Calibrate your likelihood of failure skills with other arborists
  • Explain where likelihood of failure decision-making research is heading

*Full training in the use of VALID is a 2 day course that will be running later this year

This course entitles you to 7 CEU's see this link link 


Course Content:

  • Engineering principles, bio-mechanics, and trees
  • Safety factors and strength-loss
  • What does sonic tomography tell you about breaking safety
  • How useful and how bad is drilling?
  • The Static Load Test
  • The component parts of likelihood of failure
  • VALID Tree Risk-Benefit Assessment
  • Field exercises – Significance of decay assessment
  • Field exercises – Likelihood of Failure calibration exercises


“David Evans provided a masterclass on how to deliver an engaging presentation with unique content….  It was the last talk, so those who left early really missed out”

Jeremy Barrell – Barrell Tree Consultancy, UK


"VALID has changed the way I look at tree risk assessment."

Jeff Opar - ISA Tree Academy Workshop, Fort Worth

About the Speakers

Frank Rinn studied Physics at Glassen and Heidelberg University. After completing his master thesis, Frank developed the method of needle resistance drilling and eventually started his own company, RINNTECH. Frank owns national and international patents and trademarks such as RESISTOGRAPH® and ARBOTOM®. Frank is an expert in inspecting trees and timber structures. He gives lectures and training and spends much of his time volunteering in the arboriculture industry world-wide and as the Executive Director of ISA Germany.

David Evans is the Director of VALID; a non-profit organisation delivering training and guidance in tree risk-benefit assessment and management. VALID is a ground-breaking approach to tree risk assessment which is a best of worlds, third way, that marries the benefits of both quantitative numbers and qualitative words. The VALID prototype was recently presented at the UK Arboricultural Association’s 50th conference, to considerable acclaim.

David has presented at many international conferences, and last year introduced the ‘Likelihood of Failure Club’ part of VALID to the sold-out Tree Academy Workshop as part of the ISA conference in Fort Worth. In February, he completed a 6-city tour of New Zealand and Australia, where he played Likelihood of Failure Club with more than 250 arborists.

Before he set up VALID, for more than a decade, David was one of the lead Quantified Tree Risk Assessment (QTRA) trainers, and an invaluable contributor to QTRA’s past development. He is currently dipping his toes back into the academic stream by undertaking a PhD into Tree Risk-Benefit Assessment.

Module Pre-requisites:


Terms of Cancellation or Amendments to details

  • We reserve the right to cancel courses and refund applicants if there is insufficient demand.
  • A FULL charge will be applied to any booking cancelled less than 10 working days before the event.
  • A £30 administration charge may be applied to changes made to bookings that have been received and acknowledged.

For all course bookings outside the UK and Europe, please email