Counsel benefits when they have some knowledge of the forensic engineering investigative process that is followed by an expert.  The process determines why a structure failed or an accident happened.  The process results in a thorough investigation leading to an objective opinion rendered with considerable certainty.

This item identifies and describes the steps in the process. The process is followed regardless as to whether the professional engineer is retained as a consulting expert or a testifying expert.

A structure is anything in the built environment, including alterations of the natural environment like highway embankments and earth and rock slopes.  A failure can involve total collapse of a structure or its inadequate performance.

There are three fundamental components to the forensic engineering investigative process:

• Acquisition of data
• Analysis of data
• Presentation of conclusions and opinions

Rigid formulae for investigating failures and accidents do not exist.  But all forensic engineering investigations contain the following steps to a greater or lesser degree.

1. Document Review
2. Visual Assessment
3. Field Investigations
4. Laboratory Investigations
5. Research
6. Follow-up Investigations
7. Data Analysis and Formulation of Opinion
8. Report

Field investigations can be broken down further:

1. Describe the Failure or Accident
2. Survey and Document the Damage to the Structure
3. Determine how the Structure is Built
4. Determine the Site Conditions

Most of the investigation involves gathering data and most of the report – more than 3/4, involves presenting and analysing the data.  This points to the importance of the data gathering.  The degree of certainty in the final opinion of the cause of the failure is often a function of the amount of data gathered and the budget for this.

Following is a brief description of each step in the investigative process:

1. Document Review

Documents provided by counsel during the initial briefing are important in a forensic engineering investigation.  They sometimes provide the only data available to an engineer investigating a failure. Documents include items like the following:

1. Client narrative
2. Discovery transcripts
3. Text
4. Drawings and maps
5. Photographs
6. Maintenace records

Additional published documents almost always researched by a professional engineer include:

1. Legal surveys and descriptions
2. Land development and drainage plans
3. Aerial photography of the area of the site
4. Topographic and contour maps
5. Surficial and bedrock geology maps
6. Agricultural soil maps
7. Hydrological maps and studies
8. Hydrogeological maps and studies
9. Flood plain mapping
10. Mining activity mapping
11. Environmental reports

Documents like these are often studied a number of times during the different stages of an investigation.

Information from the documents along with an initial site visit and visual assessment enables the engineer to plan the different investigations based on what he thinks caused the failure or accident – his initial hypothesis.  Investigations are designed to confirm, revise, or refute the initial hypothesis.

In checking the hypothesis, engineering investigations determine:

1. What took place during the failure or the accident,
2. The nature and extent of the damage or inadequate performance,
3. How the structure was built, and its conformance to the design and construction plans, and,
4. The nature of the area the structure is in and the ground beneath the structure

2. Visual Assessment

This step involves visiting the site as soon as possible after the failure or accident, walking and poking around the site to get a feel for where things are and the nature and extent of the damage, and examining exposed surfaces.  It’s a very simple task – not very technical at all, but invaluable in getting a feel for the scene and bringing the documents to life.

Measuring in a number of different ways characterizes the investigation carried out by professional engineers.

3. Field Investigations

Describe the Failure or Accident

This step involves learning what happened – getting a description of the failure or accident by interviewing witnesses.  This discription may be gleamed from the documents but talking with people who were there and saw or experienced the failure – particularly if it was a sudden collapse of a structure, or an accident, is much better.

Survey and Document the Damage to the Structure

This step involves recording the damaged condition of the structure that has collapsed or does not perform properly.  The condition is recorded by means of tasks such as the following:

1. A visual examination and description of the structure’s condition,
2. Measuring the extent and location of the damage, and
3. Photographing and videotaping the damage.

This should be done as soon as possible after the failure before data and evidence are altered or lost.  The information enables a before-after comparision to be made after the next step is completed.  This type of comparison is often helpful.

Determine how the Structure is Built

How the structure is built, whether or not it comforms to the design, and the adequacy of the design is determined in this step.  Also, whether or not the design reflects the standards of the day.  This information is obtained from various plans and research of standards and checking these against the structure on site.  Tasks involved in this step include the following:

1. Obtaining copies of the design and construction drawings – often quite similar
2. Checking the design that it conforms to good engineering practice
3. Checking that the construction drawings conform to the design
4. Obtaining a copy of the as-built drawings – drawings that record changes made during construction due to various reasons
5. Checking that the existing structure conforms to the as-built drawings.  This involves examining and measuring the different components of the structure.  It often involves taking things apart or using remote sensing techniques to detect what is below the surface.  To facilitate this examination, drawings of the damage might be superimposed on the as-built drawings.  This superimposing would eventually be done during the data analysis (see below)
6. In the absence of drawings – often the case for older structures, measure the structure and prepare drawings, and then supepimpose sketches of the damage

How many of these tasks are carried out and in what detail depends on the situation, the structure, and the failure.  Sometimes very little of the above is done.  Sometimes it’s enough just to measure and prepare sketches of the damage and view and study the structure with these sketches in hand.

Determine the Site Conditions

The site is the area the structure is on and the terrain beyond the site including other structures.

The site conditions of interest at this stage of the investigation include:

1. The lay of the land; the topography
2. Surface features like bedrock exposures, sinkholes, and wet land
3. Drainage features like ponds, lakes, and water courses (hydrology)
4. Subsurface and foundation soil and rock conditions
5. Groundwater conditions (hydrogeology)

Investigation of site conditions includes:

1. Photographing and videotaping the site
2. Aerial photography and map making
3. Topographic and elevation/contour surveys
4. Drainage studies
5. Geotechnical and foundation soil and rock investigations
6. Full scale field tests like plate load tests and pile load tests
7. Accident reconstruction

Detailed topographic and elevation surveys are usually made when the failure of a building or a civil engineering structure, or the cause of an accident, is thought to involve the terrain in which the site is located.

Drainage studies (hydrology) are made when surface or groundwater may have been a factor in a failure or an accident.

Geotechnical and foundation investigations may be necessary if the cause of the failure of a structure appears to be in the foundations or the subsurface soils.

Full scale field tests and accident reconstruction may be carried out.  This is done when these methods are assessed as the most reliable means of gathering data on the effects of the terrain and features in it on the failure or the accident.

4. Laboratory Investigations

It is often necessary to carry out laboratory tests to determine the chemical, physical, mechanical, strength, and/or drainage properties of materials used in construction at the site of a failure or an accident.  It might be necessary to measure the toxic fumes emitted by a compound or product used in construction.

Typical materials used in construction are soil, rock, steel, concrete, wood, plastic, adhesives, asphalt, and masonry products.

Composite materials like asphalt or reinforced concrete can be taken apart in a laboratory to determine how the material was formed.  For example, the location, type, and size of reinforcing steel in a reinforced concrete slab that failed.

5. Research

To some extent, research studies and investigations – desk studies in some disciplines, are on-going like document review during a forensic engineering investigation.

The work often involves literature searches, telephone and internet work, and leg work to sources outside the office like libraries and the offices of persons to interview and consult with.

It also involves research and study of aspects of the engineering investigation that have assumed some relevance.  For example, past mining activity in an area, the standard of care at the time the structure was designed and constructed, the shrinkage properties of a fill material, and the different modes of failure of a soil-steel bridge.

Research also identifies and gathers together all information in appropriate categories relevant to the investigation of the failure (see Document Review above).  This would be information usually not contained in the documents provided by counsel during the initial briefing.  Information like original construction and as-built drawings, geotechnical and environmental reports, and published mapping of the area

6. Follow-up Investigations

This task of carrying out one or more follow-up investigations results from the need to “follow the evidence”.  This concept hardly needs explaining to counsel.  It is equally important in a forensic investigation.  Data will be gathered and evidence uncovered during a previous investigation that suggests another line of enquiry should be followed up or another area investigated.  This is like cross-examination during discovery uncovering evidence that suggests a new line of questioning.

Implicit in the fact that there might be evidence that should be followed up is the possibility that the initial hypothesis on the cause might need to be revised or rejected completely.

The possibility of the need for follow-up investigations is a fact of life during forensic engineering investigations.

7. Data Analysis and Formulation of Opinion

In analysing and reasoning to a conclusion, the data from any one stage of the investigation is looked at critically – taken apart, in a sense, and each part looked at carefully, and how they are related and their interaction examined.

The data is also looked at closely to see if it is characteristic of or associated with a mode of failure or a cause based on past experience and/or mathematical calculation.  Professional engineers have identified and published typical modes of failure for the various structures in the built environment.  These are available for review and guidance to the forensic engineer during a forensic investigation.

The data from other stages of the forensic investigation are similarly looked at, and also studied to see if there is corroboration of conclusions between stages.  Pattern is looked for within individual data and amongst different sets of data.  And if there is a pattern, considering if it is typical of a known cause of failure.

At some point, when engineering judgment dictates, conclusions are drawn from the analysis and the hypothesis confirmed, revised, or refuted.  If revised or refuted then a new hypothsis is formed and this investigated with follow-up forensic investigaions.

If the initial hypothesis is confirmed then the cause of a failure has been identified and an opinion can stated.

Sometimes the data analysis and development of an opinion is quite easy.  For example, when field work uncovers a concrete floor slab that is supported by irregularly spaced columns and the type of slab that should be beneath the structure is required to be uniformly supported.  Then it’s easy to hold the opinion that the floor slab is inadequately supported.

At other times it’s complex.  For example, when there are more than 20 possible modes of failure for the collapse of a soil-steel bridge.  When the collapsed bridge is not available to examine, then the data must be analysed for each mode and the cause identified by a process of elimination.

Sometimes it’s mysterious.  Why is there a toxic odour in the concrete enclosed lower level of a structure and the lighter-than-air fumes are not detected in the timber framed upper levels?  A chance remark about timber structures “breathing” – are more pervious, in a sense, in engineering terms, solves the mystery as to cause.  The fumes in the upper levels diffuse through the exterior timber walls to the outside of the structure.

8. Report

The report, in particular, the written report, is an important step in a professional  engineer’s investigation of a failure or an accident.  It is an objective documentation for the judicial system of the methods used during the investigation, the data gathered, the analysis of the data, and the reasoning to an opinion on cause.  It’s importance is highlighted by the fact that civil litigation rule changes in some provinces are resulting in the report often replacing the discovery stage.

The results of an engineer’s investigation of a failure or an accident are presented in:

1. Oral reports,
2. A written report, and,
3. Occasionally, one or more supplementary reports

If possible, an oral report is given to counsel as soon after the documents are read, an initial site visit and visual assessment completed, and an initial hypothesis formed as to cause.  The report will indicate the direction the investigation appears to be leading.  This will give counsel an early indication as to whether the professional engineer will serve as a consulting expert or as a testifying expert.

A written report is provided at completion of the investigation.  It is prepared on instruction of counsel for the court and judge and submitted to counsel.

The need for supplementary reports might depend on whether or not new evidence is found during discovery, in follow-up investigations, or presented in rebuttal reports.

The outline of a report will vary depending on the nature of the failure or accident and the extent of the investigation.  Many will be in chronological order, generally the order of the steps in the forensic engineering investigative process.  The process is a series of investigations and follow-up investigations.  My reports generally:

1. Describe the individual investigations,
2. State the purpose or reason for carrying out each investigation,
3. Identify the data obtained, and,
4. If possible, do a little preliminary analysis and reasoning and comment on the validity of the initial hypothesis.

References

The foregoing is based on several sources.  The citations are not complete:

1. ASCE, Guidelines for failure investigation, 1989
2. ASCE, Guidelines for forensic engineering practice, ed., Gary L. Lewis, 2003
3. ASCE, Guide to investigation of structural failure, Jack R. Janney, 1986
4. Mr. Jack Osmond, NSPL, Affinity Contracting, Halifax
5. Expert Witnessing; Explaining and Understanding Science, ed., Carl Meyer, 1999
6. Steps in the civil litigation process

Copyright 2012, Eric E. Jorden. All rights reserved

Preparing and filing a Statement of Claim with the court – typically along with the Notice of Claim, is the second of four steps collectively known as the Pleadings in the civil litigation process.

A professional engineer or other expert can be particularly valuable at this stage.  Our forensic engineering investigations provide the evidence that establishes the technical facts and identifies the technical issues on which a claim for damages in the built environment is based.

We can also evaluate the technical content of the Statement of Defence and the technical strengths and weaknesses of the defence’s response to the plaintiff’s claims.

The following assumes the early involvement of a professional engineer to ensure a Statement of Claim is technically well founded.  Early involvement avoids the engineer or expert having to play catch up, and counsel finding himself out on a limb with a Statement of Claim that is not as technically complete and as well founded as it might have been.

The role of a professional engineer during previous steps in the civil litigation process was described in earlier postings – see the following references.  Our role in subsequent steps in the process through to trial will be described in future postings.

• Notice of Claim
• Statement of Claim
• Statement of Defense
• Affidavit of Documents

The Statement of Claim is more particular than the Notice of Claim.  It is a document that further describes the parties and defines their relationship(s) with each other.  The Statement of Claim is a listing of the facts.  In construction and engineering claims, the parties oftentimes have a formal contract.  In general negligence claims, the parties are often in proximity such that one owes the other a legal duty – to do or not do something.

Counsel for the plaintiff prepares a Statement of Claim that sets out the disputed issues and the claims the wronged party, the plaintiff, is making against the defendant.  The claims would include, for example, the relief sought – what the plaintiff wants the court to award.  This can be very general, such as claiming damages, costs, and interest.  It does not usually state exact dollar figures.

The Statement of Claim is served on the defendant by the plaintiff, typically through a process server who is engaged to personally hand-deliver the document to the defendant.  The person delivering the document swears an affidavit that this was done.

A professional engineer can assist counsel in the following ways during preparation of a Statement of Claim: :

1. Review narrative from the complainant for technical evidence
2. Review available evidence of lay witnesses, and other experts and specialists
3. Complete the engineering investigation of the cause of the failure or accident, the technical issues and questions identified by counsel, and any follow-up investigations found to be necessary.  (Some preliminary engineering investigations during earlier steps in the civil litigation process would have alerted counsel as to the direction the engineering investigation seemed to be leading with respect to counsel’s interests)
4. Analyse the data gathered during the investigations and establish the cause of the failure or the accident 
5. Document the reasoning leading to the identification of the cause
6. Define the technical issues between the parties as established during the investigations 
7. Identify the technical facts relevant to the cause of the failure or accident
8. Identify the evidence supporting the facts
9. Review the Statement of Claim and confirm the correct understanding of the technical facts and issues in the claim the plaintiff is making against the defendant
10. Identify parties that could be involved in the engineering failure or accident that have not been named in the Statement of Claim
11. Prepare preliminary design of repair of the damaged structure 
12. Prepare preliminary estimate of the cost of repair
13. Prepare a report on the instruction of counsel describing the investigations, the data gathered, the analysis and reasoning, the findings, the conclusions, and the opinion formed
14. Review the Statement of Defense, counter claims, and cross claims – and counsel’s response to these statements, and ensure correct understanding of technical facts and issues 
15. Assess the technical strengths and weaknesses of the case for the defense, the counter claims and cross claims

References

1. Steps in the civil litigation process.  Published August 28, 2012
2. The role of a professional engineer in counsel’s decision to take a case.  Published June 26, 2012
3. The role of a professional engineer assisting counsel prepare a Notice of Claim.  Published July 26, 2012
4. Stockwood, Q.C., David, Civil Litigation, A Practical Handbook, 5th ed., 2004, Thompson Carswell
5. ASCE Guidelines for Forensic Engineering Practice, 2003, American Society of Civil Engineers

I read the report in yesterday’s Chronicle Herald about flying pieces of metal injuring four people on a popular ride in Yarmouth.

It occurs to me at this distance that this should be a fairly easy failure to investigate with a visual assessment by perhaps an experienced mechanical engineer.  For certain, to at least enable a tentative statement of cause.

This is because the surfaces from which the metal came loose are likely to be exposed to view.  And because there are likely to be other units (chairs?) in the ride apparatus that are identical with the metal still in place.  This would afford a before and after comparision of the in-place condition of the pieces of metal.  This type of comparision can yield good evidence.

(A failure in engineering occurs when something in the built environment doesn’t perform properly)

A visual assessment doesn’t sound very technical but it is always valuable and sometimes all that is necessary.  And it is an essential part of the main steps in the failure investigation process:

• Acquisition of data
• Analysis of data
• Formulation of opinion

One time, I investigated the reason a piece of ice fell from a structure and struck and injured a person.  My investigation was based almost entirely on a visual assessment of the exposed surfaces of the structure.  I did this to some extent from a distance with binoculars and a camera with telescopic lens.

I also was able to compare the condition of the part of the structure involved with other unaffected parts of the structure and other structures in the area that were the same.

I analysed the data – largely taken from a visual assessment, formed my opinion, submitted my report, and, I understand, a dispute that had been ongoing for several years was resolved within a few months.

This situation with the falling ice seems very similar to the situation in Yarmouth with the flying pieces of metal.

At the very least, an initial hypothesis could be formed as to the cause of the problem based on a simple visual assessment.  This hypothesis could then be investigated by more detailed forensic engineering investigation, if this in fact is necessary.

The Nova Scotia Department of Labour are investigating and I’m certain we’ll know the answer soon enough.

References

American Society of Civil Engineers, Guidelines for Failure Investigation, 1989

The Chronice Herald, Thursday, August 2, 2012, page A6

In addition to the potentially low crop yield being reported in the local and national Canadian and U.S. press.

Reports from the Annapolis Valley in Nova Scotia, a prime agricultural area, note  the worst drought conditions in 10 years.  I spoke with one grower several weeks ago who incredulously noted that rain had not fallen on his crops in two months.  This in an area – eastern Canada, where a low pressure system goes through about every three or four days, often accompanied by rain.  We are fond of saying down here that the weather builds character.  I can just imagine what my grower is saying now, possibly unprintable.

Forensic engineers consider the effects of drought in some investigations.

Effects of drought

Foundations of buildings and civil engineering structures can settle or subside in drought conditions.  This can happen to both new and old structures.  This kind of settlement is in addition to that usually predicted by geotechnical engineers during foundation design.  That is, settlement due to the more normal loads on a structure – see the item published July 10, 2012 for comment describing more normal design loads.

(Geotechnical engineers investigate the physical properties of soils and rocks and advise design engineers of the effects of these properties on structures)

Foundation settlement due to drought is not usually considered in engineering design when assessing the loads on a structure in eastern Canada.  This is because this type of settlement is often slight.  Also because there is seldom a scarcity of rain in eastern Canada so we seldom experience drought conditions.

But, it should be considered elsewhere in Canada and the U.S.  And in the future down east considering the possible effects of global warming on climate change as suggested by some. And maybe during the present drought.

(Engineers think of loads as something than can affect a structure and most be provided for or accommodated in design.  There is certainly an argument for considering the effects of drought as a load on a structure even if dismissed quickly most of the timel)

Is this too esoteric a matter for engineers to be concerned with – the effects of drought on conventional structures in the built environment?  I don’t think so.

Let’s not be too quick to dismiss slight foundation settlement due to drought as insignificant.  It can be very significant to transformer foundations in substations and to the foundations of free standing, un-guyed towers and to wind turbines. (Substations are components of an electrical power distribution system)

These types of structures are quite sensitive to foundation settlement.  They are sensitive to a few millimetres settlement, like, less than 5 millimetres.  Whereas more conventional structures – such as many low-rise buildings, can tolerate in the order of 25 millimetres, and some structures somewhat more than this.

How drought causes foundation problems and damage

How can drought cause foundation settlement?  It’s quite easy and the reason will take you back to your high school physics class.

A drought causes the watertable to drop.  We all know about that – think dug wells going dry.  When the watertable drops the groundwater “drains” out of the soil above.  The soil is no longer submerged below the watertable.  The recently drained, relatively dry soil above the watertable – due to the drought, is now heavier.  Think back to your high school physics and the fact that the dry unit weight of a soil is heavier than the submerged unit weight.

Relatively dry soil will settle due to its (increased) weight, due to its increased “self weight”.  Foundations on soil that is settling or subsiding will also settle – go down with the subsiding soil.  And this can be caused by drought as we saw above.

For example, the gardeners amongst us have seen the soil in a recently planted container settle over a period of days.  This is due to the self weight of the soil causing compression or settlement within the soil.  The increased self weight of a soil that is suddenly above the watertable due to a drought will have the same effect – cause the soil to compress.

Another example is the depression across the road at the former location of a construction trench that has been filled in with soil.  A lot of this depression is due to compression within the soil due to its self weight.

The same engineering principle underlies these examples as does the effects of drought.

I can easily imagine drought causing significant settlement that is greater than slight settlement, particularly with recently designed and constructed structures in areas that have not experienced drought before.

The evidence for this lies in Mexico City.  The city has been settling for years, totalling several feet in some areas and causing much damage as you can imagine.  This settlement is due to a lowering of the watertable.  The watertable was lowered when water was pumped from wells in the city over many years.

Pumping is a different kind of assault on the watertable than drought.  But the soil doesn’t care what causes the watertable to drop and its self weight to increase.  When this occurs the soil is going to settle causing greater or lesser damage to any foundations above.

The drought occurring now can conceiveably cause foundation problems.  But a forensic engineer investigating a specific problem would need to look at factors like the sensitivity of the foundation to settlement, the magnitude of the drop in the watertable, the soil, and historical records of drought in an area.

An experienced geotechnical engineer in many parts of North America will consider the effects of drought on a structure.  They might see it as a load on a structure the effects of which – increased foundation settlement, must be provided for by a design engineer.

An experienced forensic engineer will consider the effects of drought when investigating the cause of the poor performance or complete collapse/failure of a structure.

Civil litigation tentatively begins when counsel meets with a potential client.  The purpose is to gather information to help him or her assess the merits of the case and decide if he should take it.

A professional engineer could have a role in this meeting, or in consultation shortly afterwards.  This is particularly the case if the legal and technical issues are likely to be complex requiring extensive engineering investigation to support a reliable opinion.

                 “I’ve seen cases that should never have gone forward …”

I’ve seen cases that should never have gone forward.  Not because of a lack of technical merit but because of the client’s limited financial resources to bear the cost of the forensic engineering investigation necessary to determine the cause of the problem.  These would be costs learned about after a claim was filed and discoveries held – and only after a professional engineer was retained to investigate the technical issues.

During the meeting, counsel obtains information from the client’s description of the problem and the damages he believes he has incurred, documents provided by the client, knowledge of witnesses, answers to questions raised by the lawyer, the lawyer’s past experience of similar matters, and comments by an expert on the technical issues.

One of several important considerations covered by the meeting and the lawyer’s review of the facts is the need for an expert on the case.  An expert can make or break a case and if thought to be necessary should be chosen carefully and retained early (Ref.1).  Even if only retained briefly to support counsel’s assessment of merit, in the event counsel decides not to take the case.

If a professional engineer is not included in the meeting, then counsel might confer with one later during his review of the facts prior to making a decision about taking the case.  The engineer would, of course, review the information from the meeting, particularly the documents, and identify the technical issues prior to counseling the lawyer.

The engineer can also provide very preliminary comment on the engineering investigation needed to address the technical issues and to formulate an opinion on the cause giving rise to them.  The engineer would educate counsel by outlining some of the tasks that would need to be carried out during an investigation and the time to do these – factors that can have a significant impact on the cost of litigation.

If the technical issues are complex – and the engineer can certainly help determine that, the monetary claim for damages likely to be substantial, and the lawsuit quite lengthy then this will affect the client’s litigation costs.  The client’s ability to bear these costs is important information in counsel’s decision on taking the case.  An engineer can have a role in assisting counsel make that decision.

Following are tasks that a professional engineer – or any expert for that matter, could carry out during or shortly after counsel’s first meeting with a potential client to assist counsel’s decision about taking the case:

1. Attend and audit the meeting for technical issues, or meet with counsel shortly afterwards
2. Review client’s descriptions of the problem and the reasons for claiming damages
3. Read available documents
4. Review witness’ statements as soon as taken by counsel
5. Begin identification of potential technical issues
6. Begin identification of technical documents counsel to seek
7. Familiarize counsel on the typical stages and tasks in a forensic engineering investigation, the fact of unexpected follow-up investigations, the fact that investigations can lead in unexpected directions, the time required, and the difficulty estimating costs 
8. Identify physical evidence, tangible exhibits and possible demonstrative evidence
9. Brief counsel on parties that might be involved in the potential litigation and their relationship to the technical issues
10. Provide information that would facilitate early settlement
11. Note unfavourable evidence for the potential client’s claim
12. Remind counsel that only one side of the story is known.  The opponent’s story and documents could give rise to a small shift in the technical facts and alter the complexion of the claim
13. Tentatively assess the technical merits of the case with respect to the potential parties
14. Outline preliminary engineering investigation and the major tasks involved
15. Speculate on follow-up investigations
16. Identify specialists that may be required
17. Speculate on the order of magnitude of investigative costs
18. If counsel decides to take the case, and position letters are appropriate, ensure that demand letters, and responses, are based only on well-established technical facts and data as known at the time

References

1. Stockwood, Q.C., David, Civil Litigation, A Practical Handbook, 5th ed, 2004, Thompson Carswell