Regulation, Safety, Ethics and Governance

Introduction and Context

Transportation is not merely the physical movement of people and goods. It is a regulated socio-technical system in which vehicles, infrastructure, operators, public authorities, employees, customers, communities and digital platforms interact. For materials managers, regulatory and ethical competence is therefore a strategic capability. A transport decision that reduces freight cost but violates licensing conditions, weakens driver safety, mishandles hazardous materials or compromises shipment data can create legal, financial and reputational exposure greater than the original saving.

Transport regulation seeks to balance several public interests: safety, market access, environmental protection, labour welfare, consumer protection, national security and fair competition. The specific rules differ by jurisdiction and mode, but the underlying management questions are widely applicable:

• Who is legally permitted to provide or operate a transport service?
• What standards apply to vehicles, infrastructure, drivers and cargo?
• Who bears responsibility when loss, delay, injury or pollution occurs?
• How should hazardous materials be classified, packed, documented and handled?
• How can organizations prevent bribery, discrimination, fraud and conflicts of interest?
• How should operational and personal data be collected, shared, secured and retained?

This chapter develops an integrated governance perspective. It does not substitute for jurisdiction-specific legal advice. Regulations must always be verified with the relevant transport authority, customs authority, labour regulator, environmental agency and applicable international instrument.

Learning Objectives

By the end of this chapter, the learner should be able to:

1. Explain the purposes and architecture of transport regulation.
2. Distinguish licensing, certification, authorization and inspection requirements.
3. Analyse contractual liability, insurance and claims allocation in multimodal transport.
4. Apply the principal control logic for hazardous materials and dangerous goods.
5. Evaluate labour, occupational health and road-safety risks.
6. Design ethical procurement, anti-corruption and fair-contracting controls.
7. Develop a practical data-governance framework for transport information.
8. Integrate compliance into supplier selection, performance management and strategic decision-making.

1. The Architecture of Transport Regulation

1.1 Public and private sources of control

Transport governance arises from several overlapping sources:

A useful distinction is between hard law, which is enforceable by public authority, and soft law, such as voluntary standards, codes and industry guidance. Soft law may become commercially important when customers, insurers, lenders or public-sector buyers make compliance a condition of doing business.

1.2 Regulatory objectives

Regulation is not a single constraint. It performs several functions:

1. Risk reduction: controlling hazards that private contracting alone may not adequately manage.
2. Information correction: requiring disclosures, labels, records and inspections where customers cannot easily assess safety.
3. Market ordering: preventing unsafe operators from gaining advantage through non-compliance.
4. Externality management: addressing congestion, emissions, noise, accidents and environmental damage.
5. Rights protection: safeguarding workers, passengers, communities and data subjects.
6. System resilience: ensuring continuity during disasters, cyber incidents or supply disruptions.

1.3 Licensing and authorization

A transport enterprise may need several distinct permissions. A business licence establishes the legal existence of the enterprise; an operating authority permits a particular transport activity; a vehicle registration identifies the vehicle; a professional or commercial driving licence qualifies the driver; and a route, terminal, customs or dangerous-goods permit may impose additional conditions.

Managers should not treat a licence as a permanent entitlement. Licences commonly depend on continuing conditions such as financial capacity, vehicle fitness, insurance, driver competence, tax status, operating hours and safety records. A robust licence register records the issuing authority, scope, expiry date, conditions, responsible owner and evidence of renewal.

1.4 Compliance as a management system

Compliance is strongest when embedded in the operating system rather than assigned exclusively to a legal department. A practical cycle is:

Identify → assess → control → monitor → report → improve.

Risk assessment should consider both probability and consequence. A simple prioritization model is:

Here, R_i is the relative risk score for hazard i, P_i is its assessed probability and C_i is the consequence score. The expression is a prioritization aid, not a universal measure of legal risk. Scores must use defined scales, consistent assessors and documented assumptions. Low-frequency catastrophic events may require controls even when their numerical score is uncertain.

2. Liability, Contracts and Insurance

2.1 The structure of transport liability

Liability may arise from contract, negligence, breach of statutory duty, product defect, environmental harm, employment law or criminal conduct. The relevant question is not simply “Who owns the vehicle?” It is “Which party controlled, caused, assumed or legally bears the relevant risk?”

Common parties include the shipper, consignee, carrier, freight forwarder, warehouse operator, terminal operator, customs broker, subcontracted carrier and technology platform. A single shipment may therefore involve several legal relationships.

Important liability events include:

• loss, theft or damage to cargo;
• delay and consequential business interruption;
• personal injury or death;
• pollution and hazardous-material release;
• customs non-compliance;
• vehicle or infrastructure damage;
• data breach and unauthorized disclosure.

2.2 Contractual allocation of risk

A transport contract should clearly define the service, collection and delivery points, transfer of custody, packaging responsibilities, documentation, permitted subcontracting, service levels, claims procedure, limitation of liability, insurance, force majeure, confidentiality, audit rights, dispute resolution and termination.

Liability clauses must be interpreted alongside mandatory law. A contract cannot always exclude liability for fraud, wilful misconduct, death, personal injury, environmental offences or statutory duties. Some jurisdictions also impose mandatory carrier liability regimes or limits that parties cannot contract out of.

The following distinction is essential:

• Direct loss: physical cargo damage or a directly measurable transport cost.
• Indirect or consequential loss: lost production, lost sales or reputational damage, often treated differently by contract.
• Delay loss: loss caused by failure to meet a delivery commitment.
• Force majeure: an extraordinary event outside reasonable control, subject to the exact contractual wording and mitigation duties.

2.3 Incoterms and transfer points

In international procurement, Incoterms® rules clarify selected obligations, costs and risk transfer between buyer and seller. They do not by themselves settle every issue of title, payment, insurance, sanctions, product compliance or dispute resolution. Materials managers must therefore avoid treating an Incoterm as a complete transport contract.

The operational control question is: at what precise event does risk transfer? For example, risk may transfer when goods are handed to a carrier, loaded on board a vessel, delivered to a named place or made available for unloading. The named place and version of the rule must be stated accurately.

2.4 Insurance and claims governance

Insurance does not eliminate risk; it finances specified risks subject to exclusions, deductibles, limits, warranties and reporting conditions. Relevant covers may include motor liability, cargo, employer’s liability, public liability, pollution, cyber and professional indemnity.

A sound claims process preserves evidence immediately. It should record the shipment identity, condition at handover, seal numbers, photographs, temperature or sensor data where relevant, driver and vehicle information, incident timeline, witness accounts, police or regulatory reports and mitigation actions. Delay in notification can prejudice coverage.

2.5 Subcontracting and due diligence

Outsourcing transport does not automatically outsource accountability. The contracting organization remains exposed to negligent supplier selection, inadequate instructions, poor monitoring and misleading representations. Due diligence should verify legal identity, licences, insurance, safety performance, financial stability, labour practices, sanctions status, cybersecurity controls and subcontracting arrangements.

3. Hazardous Materials and Dangerous Goods

Hazardous-material regulation is based on the possibility that a substance may harm people, property or the environment during storage, handling, transport or emergency response. Rules differ by mode but commonly reflect internationally harmonized classification and communication principles.

3.1 Classification and communication

A dangerous good is classified according to its physical, chemical or biological hazard. Typical classes include explosives, gases, flammable liquids, flammable solids, oxidizers, toxic substances, infectious substances, radioactive materials, corrosives and miscellaneous hazards. The classification determines packaging, quantity limits, vehicle or vessel requirements, segregation, documentation, labelling, emergency information and training.

The shipper is usually responsible for accurately identifying and declaring the substance, although responsibilities may be distributed among consignor, packer, carrier, loader and consignee. A generic product name is inadequate where the rules require a technical name, classification, identification number, packing group or other prescribed information.

3.2 Control sequence

A practical dangerous-goods control sequence is:

1. Identify the substance and obtain its current safety data sheet.
2. Determine the applicable mode, jurisdiction and regulatory instrument.
3. Classify the hazard and establish any quantity threshold or exemption.
4. Select approved packaging and verify compatibility.
5. Apply required marks, labels, placards and handling instructions.
6. Prepare transport documents and emergency information.
7. Confirm trained personnel, vehicle suitability and route restrictions.
8. Segregate incompatible materials.
9. Inspect loading, securing, seals and documentation.
10. Prepare incident, spill and emergency-response procedures.

The most dangerous failure is often not a dramatic packaging defect but inaccurate information. Misclassification can lead to incompatible loading, ineffective emergency response, unlawful routing and severe liability.

3.3 Security and chain of custody

Some dangerous goods also present security risks. Controls may include background screening where lawful, restricted access, inventory reconciliation, route confidentiality, secure parking, seal management, geofencing and escalation of unexplained deviations. These measures must be proportionate and must not undermine legitimate worker rights or emergency access.

3.4 Environmental responsibility

Hazardous-material governance extends beyond delivery. Organizations must plan for spills, contaminated packaging, waste disposal, vehicle emissions, wash-water and end-of-life containers. The “polluter pays” principle, extended producer responsibility and environmental permitting may apply depending on the jurisdiction.

4. Labour, Occupational Health and Transport Safety

4.1 The human-risk system

Transport accidents are rarely explained by a single factor. They arise from interactions among fatigue, time pressure, road design, vehicle condition, training, weather, communication, supervision and organizational incentives. A mature safety system therefore investigates underlying conditions rather than blaming the person nearest to the event.

Core controls include:

• competency-based recruitment and induction;
• valid licences and medical fitness where required;
• fatigue and working-time management;
• seat-belt, speed and mobile-device policies;
• preventive maintenance and defect reporting;
• safe loading, weight distribution and securing;
• journey planning and approved rest locations;
• incident and near-miss reporting;
• emergency drills and first-aid capability;
• protection from retaliation for reporting hazards.

4.2 Safety culture and just culture

A safety culture is the pattern of shared expectations and behaviours concerning risk. A just culture distinguishes honest error, at-risk behaviour and reckless misconduct. Honest error should normally trigger system improvement; deliberate violation may require discipline. Without this distinction, employees conceal near misses and managers lose valuable information.

Leading indicators include training completion, preventive-maintenance compliance, defect closure time, near-miss reporting and corrective-action quality. Lagging indicators include collisions, injuries, spills, fatalities, cargo loss and regulatory enforcement. Neither category is sufficient alone: a low incident rate may indicate excellent control or under-reporting.

4.3 Contractor and migrant-worker protection

Transport supply chains often contain small carriers, agency labour and migrant workers with limited bargaining power. Ethical and legal procurement should address minimum wages, working hours, freedom from forced labour, non-discrimination, safe accommodation where provided, grievance channels and the right to refuse imminently dangerous work. Cost pressure must not be transferred to workers through unsafe scheduling or unlawful deductions.

5. Ethics, Anti-Corruption and Fair Contracting

5.1 Ethical risk in transportation

Transport is vulnerable to corruption because it involves border crossings, permits, inspections, scarce capacity, discretionary enforcement and urgent cargo. Risks include bribes, facilitation payments, kickbacks, collusion in tendering, conflicts of interest, false mileage, phantom deliveries, invoice fraud, gifts to officials and manipulation of accessorial charges.

An effective ethics programme combines:

• visible leadership commitment;
• a clear code of conduct;
• risk-based third-party due diligence;
• segregation of duties;
• competitive and documented procurement;
• approval thresholds;
• gifts and hospitality controls;
• conflict-of-interest declarations;
• confidential reporting channels;
• investigation and disciplinary procedures;
• accurate books and records;
• periodic testing and remediation.

5.2 Fair contracting

Fair contracting does not mean identical treatment of every supplier. It means transparent, proportionate and consistently applied criteria. Tender documents should define the scope, evaluation method, insurance, safety standards, data obligations, payment terms, change-control process and termination rights before bids are evaluated.

Particular care is needed with small carriers. Excessive payment delays, unilateral deductions, indefinite liability, retroactive rate changes and unrealistic service requirements may create both ethical and operational risk. A contract that is legally enforceable may still be commercially abusive and may encourage unsafe behaviour.

5.3 Competition and collusion

Bid rotation, market allocation, identical unusual pricing and coordinated withdrawal can indicate collusion. Procurement teams should preserve bid records, restrict access to commercially sensitive information, separate specification design from evaluation, rotate panel members where appropriate and escalate suspicious patterns. Competition law is jurisdiction-specific; legal counsel should review high-risk arrangements such as exclusivity, information exchange and joint bidding.

6. Data Governance and Digital Transport

Transportation generates bills of lading, delivery records, geolocation, driver identity, vehicle telemetry, customer information, invoices, customs data and sensor readings. Digitalization increases visibility but also creates privacy, cybersecurity and algorithmic risks.

6.1 Data principles

A practical data-governance framework applies the following principles:

1. Purpose limitation: collect data for defined legitimate purposes.
2. Data minimization: collect only what is reasonably necessary.
3. Accuracy: correct inaccurate operational or personal data.
4. Access control: grant access according to role and need.
5. Retention control: delete or anonymize data when no longer required.
6. Security: protect confidentiality, integrity and availability.
7. Accountability: assign owners and retain evidence of decisions.
8. Transparency: explain monitoring and automated decisions where required.

Geolocation can improve safety and proof of delivery, but continuous worker surveillance may be disproportionate. Monitoring policies should identify the purpose, information collected, access rights, retention period, legal basis where applicable and process for challenging inaccurate or unfair outcomes.

6.2 Cybersecurity and operational technology

Transport systems increasingly depend on telematics, warehouse systems, electronic logging, traffic management, autonomous functions and application programming interfaces. A cyber incident can create physical danger by disrupting routing, braking assistance, signalling, refrigeration or dangerous-goods information.

Controls include asset inventories, strong authentication, network segmentation, patch management, supplier-security requirements, backup communications, incident response, recovery testing and secure software updates. Cybersecurity must include smaller carriers and subcontractors because attackers may exploit the weakest connected party.

6.3 Artificial intelligence

AI may support route planning, ETA prediction, fraud detection, maintenance forecasting and document classification. It should not be treated as inherently objective. Training data may encode bias; predictions may be unreliable in unusual conditions; and automated decisions may obscure accountability.

Before deployment, managers should define the decision being supported, validate performance across relevant conditions, establish human override, monitor drift, protect sensitive data and document responsibility. Safety-critical decisions require a higher evidential standard than low-risk administrative automation.

7. Governance Model for Materials Managers

A governance model allocates responsibility rather than merely listing policies. The board or senior leadership sets risk appetite and receives material compliance reports. The procurement function embeds requirements in sourcing and contracts. Operations verifies licences, loading, routing and incident controls. Human resources manages competence and labour conditions. Information security governs digital risk. Legal and compliance interpret obligations and investigate concerns. Suppliers remain responsible for their own lawful operations but must provide evidence of performance.

A responsibility matrix can clarify ownership:

Performance dashboards should combine compliance, safety, service, cost and sustainability. A carrier with excellent on-time delivery but repeated safety violations should not be rated as a high-performing supplier. Weighted scorecards must include “gates” for non-negotiable requirements, such as valid licensing or dangerous-goods competence.

8. Applied Case: The Solara Components Recall Shipment

The following is an illustrative case.

Background

Solara Components, a manufacturer of industrial batteries, needed to move a time-critical shipment from a factory to an export terminal. The shipment included batteries classified under dangerous-goods rules. A low-cost carrier offered a delivery time six hours faster than approved carriers. The carrier’s operating licence was valid, but its dangerous-goods authorization had expired. The procurement buyer proposed accepting the shipment and obtaining “temporary approval” through a local intermediary.

Problem

The proposal created several risks: unlawful carriage, incorrect emergency response, insurance invalidity, bribery exposure, worker and public safety risk, and possible export delay. The urgency of the order created pressure to treat compliance as negotiable.

Analysis

The materials manager separated the issues rather than evaluating only freight cost:

• Legal: the carrier lacked a required authorization.
• Safety: the vehicle and driver’s competence for the cargo were unverified.
• Ethical: the intermediary’s proposed payment resembled a facilitation payment.
• Commercial: an incident could cause recall, terminal rejection and customer shutdown.
• Governance: the buyer attempted to bypass the approved-supplier process.

Approach and solution

The shipment was paused. The team verified the classification, packaging, labels, documents, route and emergency instructions. Two approved carriers were assessed using a documented expedited process. The selected carrier provided current authorization, trained personnel, suitable equipment and insurance confirmation. The intermediary was reported through the ethics channel, and procurement records were preserved. Solara later amended its emergency procurement procedure to require compliance approval for any expedited transport award.

Outcome

The shipment arrived within the customer’s revised window without incident. The immediate freight cost was higher than the rejected offer, but Solara avoided unlawful carriage, possible insurance denial and reputational damage. The event also revealed a weakness in supplier master-data controls: licence expiry dates were recorded, but dangerous-goods authorizations were not.

Learning points

1. Urgency changes the process speed, not the legal standard.
2. Supplier qualification must cover activity-specific permits.
3. Anti-corruption controls are especially important where permits are discretionary.
4. Compliance data must be complete, current and owned.
5. Total risk cost is more relevant than quoted freight price.

9. Challenges, Limitations and Contemporary Developments

Transport regulation is difficult to manage because requirements are fragmented across modes and borders, terminology differs, enforcement is uneven and rules change rapidly. Small suppliers may lack compliance staff and digital systems. Excessively complex requirements can unintentionally exclude capable small operators, while weak requirements can externalize risk to workers and communities.

Contemporary developments include emissions reporting, low-emission zones, alternative fuels, battery transport, autonomous vehicles, electronic freight documents, digital customs, platform work, supply-chain human-rights due diligence and resilience planning. These developments create both efficiency opportunities and governance questions. For example, alternative-fuel vehicles may reduce emissions but introduce new fire, charging, training and emergency-response requirements.

Managers should avoid assuming that certification equals performance. Audits are samples, documents may be falsified and announced inspections can miss actual working conditions. Effective assurance combines documentary review, site visits, worker voice, data analytics, incident learning and independent escalation.

Best-Practice Implementation Framework

A postgraduate-level implementation plan can proceed through eight steps:

1. Map all transport activities, jurisdictions, modes, suppliers and cargo hazards.
2. Create a legal-obligation register linked to responsible owners.
3. Segment suppliers by risk, not merely by spend.
4. Build licence, insurance, training and permit expiry controls.
5. Embed safety, ethics, data and environmental clauses in contracts.
6. Establish reporting, investigation and non-retaliation mechanisms.
7. Integrate compliance indicators into supplier scorecards and executive review.
8. Test controls through drills, audits, scenario analysis and corrective action.

The strategic objective is not zero paperwork. It is reliable control of material risks while enabling lawful, safe and resilient movement.

Chapter Summary

Transport regulation protects safety, fair competition, workers, communities, the environment and the integrity of markets. Licensing and authorization must be treated as continuing conditions, not one-time formalities. Liability depends on legal duties, operational control and contractual allocation; insurance finances selected risks but does not replace prevention. Dangerous goods require accurate classification, approved packaging, communication, trained personnel, segregation, secure custody and emergency planning.

Safety management must address organizational conditions such as fatigue, time pressure, maintenance and reporting culture. Ethical governance requires anti-bribery controls, fair procurement, conflict-of-interest management, accurate records and protection for whistle-blowers. Data governance must balance visibility with privacy, cybersecurity and accountability. AI can assist transport decisions but requires validation, human oversight and clear responsibility.

For materials managers, the central principle is integration: regulatory compliance, safety, ethics, contracting, data protection and supplier performance should be managed as one governance system. Strategic transport competence is demonstrated not by obtaining the lowest quoted rate, but by achieving lawful, safe, transparent and resilient movement at an acceptable total risk cost.

Key Terms

Regulatory compliance: Conformity with applicable laws, regulations, permits and mandatory standards.

Operating authority: Official permission to conduct a specified transport activity.

Carrier: A party that undertakes to transport goods or passengers.

Freight forwarder: An intermediary that arranges transport and related logistics services.

Liability: Legal responsibility for loss, damage, injury, delay or unlawful conduct.

Force majeure: An extraordinary event beyond reasonable control, as defined by contract and law.

Dangerous goods: Substances or articles that present specified hazards during transport.

Packing group: A regulatory indication of the degree of danger posed by certain dangerous goods.

Chain of custody: Documented control and transfer of goods from one responsible party to another.

Safety culture: Shared organizational values and behaviours concerning safety.

Just culture: An approach distinguishing human error, at-risk conduct and reckless misconduct.

Leading indicator: A preventive measure that signals the condition of a control system.

Lagging indicator: An outcome measure such as injury, collision or cargo loss.

Facilitation payment: An improper payment intended to influence routine official action.

Conflict of interest: A situation in which personal interests may improperly influence professional duties.

Fair contracting: Transparent, proportionate and consistently applied commercial contracting.

Data minimization: Collecting only data necessary for a defined legitimate purpose.

Access control: Restricting information or system access according to authorization and need.

Supplier due diligence: Risk-based investigation of a supplier before and during engagement.

Governance: The structures, responsibilities and processes through which an organization is directed and controlled.

Review Questions

Short Answer Questions

1. Distinguish a business licence, operating authority and vehicle registration.
2. Why does insurance not eliminate transport risk?
3. List four controls required for dangerous-goods transport.
4. What is the difference between a leading and a lagging safety indicator?
5. State three principles of transport data governance.

Long Answer Questions

1. Explain how liability may be distributed among a shipper, carrier, forwarder and subcontractor.
2. Discuss the relationship between safety culture, just culture and incident reporting.
3. Describe an anti-corruption control framework for transport procurement.
4. Explain how a materials manager should govern personal and operational data generated by telematics.
5. Evaluate the strategic importance of integrating regulation, safety, ethics and supplier management.

Analytical / Application Questions

1. A carrier has excellent delivery performance but repeated licence-expiry violations. Design a decision framework for continuing, suspending or terminating the relationship.
2. A shipment of corrosive chemicals is delayed at a border crossing because the documentation is incomplete. Analyse the immediate response, liability issues and preventive controls.
3. A transport platform uses AI to rank drivers by safety risk using telematics data. Assess the privacy, fairness, accountability and operational-governance issues before deployment.

Multiple Choice Questions with Answers

Question 1

Which statement best describes an operating authority?

A. Permission for a vehicle to display a registration number

B. Permission to conduct a specified transport activity

C. A contract transferring ownership of cargo

D. A record of an employee’s working hours

Correct Answer: B. Permission to conduct a specified transport activity

Question 2

What is the primary purpose of dangerous-goods classification?

A. To determine the applicable controls for handling and transport

B. To calculate the carrier’s profit margin

C. To determine the customer’s payment date

D. To replace the need for emergency planning

Correct Answer: A. To determine the applicable controls for handling and transport

Question 3

Which is a leading safety indicator?

A. Number of collisions last year

B. Number of injuries after an incident

C. Preventive-maintenance compliance rate

D. Value of cargo damaged in transit

Correct Answer: C. Preventive-maintenance compliance rate

Question 4

Why should a transport contract specify subcontracting rights?

A. To ensure that responsibility and approval requirements remain clear

B. To remove all legal duties from the primary carrier

C. To guarantee that every subcontractor charges the same rate

D. To eliminate the need for insurance

Correct Answer: A. To ensure that responsibility and approval requirements remain clear

Question 5

Which action is most consistent with data minimization?

A. Retaining every available telematics field indefinitely

B. Collecting only data necessary for a defined legitimate purpose

C. Sharing driver locations publicly to improve transparency

D. Allowing all employees unrestricted access to shipment records

Correct Answer: B. Collecting only data necessary for a defined legitimate purpose

Question 6

A facilitation payment is best described as:

A. A lawful freight discount offered to all customers

B. An insurance deductible paid after a loss

C. An improper payment intended to influence routine official action

D. A documented payment to a contracted carrier

Correct Answer: C. An improper payment intended to influence routine official action

Question 7

What is the most appropriate immediate response when a dangerous-goods authorization has expired?

A. Proceed because the shipment is urgent

B. Hide the expiry date from the consignee

C. Pause the movement and verify lawful alternatives

D. Relabel the goods as ordinary cargo

Correct Answer: C. Pause the movement and verify lawful alternatives

Question 8

Which statement about insurance is correct?

A. Insurance prevents accidents from occurring

B. Insurance finances specified risks subject to policy conditions

C. Insurance automatically covers every contractual liability

D. Insurance replaces the need for supplier due diligence

Correct Answer: B. Insurance finances specified risks subject to policy conditions

Question 9

What does a just culture generally seek to do?

A. Punish every employee involved in an incident equally

B. Distinguish honest error from reckless misconduct

C. Suppress near-miss reporting

D. Transfer all safety responsibility to drivers

Correct Answer: B. Distinguish honest error from reckless misconduct

Question 10

Why is human oversight important when AI supports transport decisions?

A. AI outputs may be biased, unreliable in unusual conditions or difficult to explain

B. Human oversight guarantees that no incident can occur

C. AI systems cannot process any transport data

D. Human oversight makes regulatory compliance unnecessary

Correct Answer: A. AI outputs may be biased, unreliable in unusual conditions or difficult to explain