Regulatory Requirements for Customs Safety Dossiers on Imported Cells

Entry

Cross-border cell shipments hit strict regulatory checkpoints at entry ports worldwide. Import authorities review safety dossiers to confirm incoming energy storage shipments pose no thermal or chemical hazards during holding, storage, or distribution. Inspection officers evaluate physical cell markings, shipping manifests, and safety summary paperwork against national dangerous goods directives.

A missing test summary sheet or an incorrect Harmonized System code triggers immediate cargo quarantine, daily demurrage penalties, and mandatory physical inspection at the importer’s expense.

Importers moving lithium-ion, lithium-metal, or advanced solid-state chemistries into major jurisdictions operate under strict dangerous goods frameworks. Border control officers rely on visual checks, document auditing, and statistical sampling to verify cargo safety before releasing goods into domestic commerce. Clearing a container through the port terminal requires a complete safety dossier demonstrating physical stability, environmental endurance, and electrical fault protection.

Harmonized System Classification Boundaries

Customs agencies classify imported battery cells using international Harmonized System codes to establish tariff rates, oversight levels, and trade control restrictions. Primary lithium cells fall under code 8506.50, covering non-rechargeable chemistries with lithium anodes such as lithium manganese dioxide or lithium thionyl chloride. Rechargeable lithium-ion cells ~ including lithium iron phosphate, lithium nickel manganese cobalt oxide, and lithium titanate formulations ~ enter under code 8507.60.00.

Sub-classifications separate loose individual cells from fully assembled battery modules, multi-cell packs, or internal power assemblies integrated within consumer devices.

Customs officials cross-check declared HS codes against physical cell datasheets to prevent tariff evasion through misclassification. For example, declaring loose secondary cells as integrated modules to bypass transportation safety filings often results in cargo seizure. Every HS entry requires direct documentation linking the physical part number to a validated dangerous goods classification sheet.

Mandatory Border Documentation Baseline

Importers assemble a standardized documentation file before cargo leaves the factory. Border clearance halts immediately when certificates carry expired dates, missing signatures, or mismatched factory names. Customs officers rely on four primary regulatory instruments during initial manifest audits.

The main safety file rests on precise technical documentation. Border inspection routines follow a set verification sequence across four core documents.

• UN 38.3 Test Summary provides authenticated proof that the cell model passed altitude simulation, thermal cycling, vibration, mechanical shock, external short circuit, impact, overcharge, and forced discharge testing under the United Nations Manual of Tests and Criteria.
• Safety Data Sheet compiled in accordance with the Globally Harmonized System of Classification and Labelling of Chemicals displays chemical composition limits, firefighting measures, physical hazard identifiers, and toxicological characteristics.
• Commercial Invoice and Packing List states the precise total cell weight, net lithium content in grams for primary cells or total Watt-hour capacity for secondary lithium-ion cells, cell packaging format, and individual lot trace numbers.
• Dangerous Goods Transport Declaration completed by trained hazardous materials personnel states the assigned UN number, proper shipping name, hazard class, packing group, and emergency response contact details.

Discrepancies in cell capacity between the commercial invoice and the UN 38.3 test summary trigger immediate holds. Customs officials verify that stated cell watt-hour ratings match the precise ranges established in official laboratory test reports.

Primary UN 38.3 Verification Mechanics

United Nations regulations require manufacturers and distributors of lithium cells to make the UN 38.3 Test Summary available across the supply chain. Section 38.3.5 of the UN Manual of Tests and Criteria sets out ten mandatory data elements for this document. Omitting any single data field invalidates the summary during customs entry verification.

Customs inspectors examine the test summary to confirm that the manufacturer’s name and address match the bill of lading. The report must state the name of the testing laboratory, the unique tracking number, and the issue date. Paragraph 38.3.5 mandates an explicit description of the cell format, nominal mass, watt-hour rating, nominal voltage, and physical shape, alongside Pass/Fail markers for tests T.1 through T.8.

UN 38.3 test summaries are required for all commercial cell import shipments under Section 38.3.5 of the UN Manual of Tests and Criteria.

The document must carry the printed name, title, and valid signature of an authorized officer representing the cell manufacturer or test facility. Digital signatures require verifiable cryptographic stamps or live online database URIs. Port clearance personnel regularly check report numbers against laboratory databases to spot forged compliance certificates.

A forged test summary results in cargo confiscation, civil monetary fines, and elevated customs audit scoring for the importing entity.

Submitting an invalid safety dossier can run up demurrage charges exceeding three hundred dollars per container per day while administrative reviews drag on. Customs holds spanning several weeks destroy product launch timelines and burn working capital through non-refundable port storage fees.

Testing

Cell safety validation requires extensive physical testing under severe mechanical, thermal, and electrical fault conditions. Reports from independent testing facilities demonstrate that a cell design tolerates operational stresses without venting, exploding, or catching fire. Import authorities review full laboratory test reports to confirm that shipped cells match the safety margins established during formal type approval testing.

Type testing establishes the baseline physical capabilities of a specific cell model family. Test engineers subject representative samples to destructive regimes simulating transport hazards, electrical short circuits, and severe temperature fluctuations. Customs compliance auditors evaluate test parameters to confirm that test conditions reflect regulatory minimum standards.

IEC 62133 and UL 1642 Test Regimes

International electrotechnical standards provide safety criteria for secondary portable cells in transit and device operation. IEC 62133-2 defines safety requirements for portable sealed secondary lithium cells containing alkaline or non-acid electrolytes. UL 1642 serves as the primary North American standard for technician-replaceable and user-replaceable lithium cells.

Compliance with IEC 62133-2 requires explicit testing of cell thermal endurance at elevated temperatures. Cells sit in a forced-air convection oven heated to 130 degrees Celsius for ten minutes; passing requires zero fire and zero explosion events during heating or cooling. The external short circuit test places fully charged cells into an environmental chamber at 55 degrees Celsius while connecting positive and negative terminals with a low-resistance wiring bridge.

Cells must demonstrate effective internal safety vent activation or current-interrupt device operation without rupture.

Lot Conformity versus Type Approvals

A type approval report validates that a single batch of prototype cells met international safety requirements at a specific point in time. It does not prove that mass-produced cells manufactured months later maintain identical internal tolerances, separator thickness, or electrode winding consistency. Customs auditors increasingly demand evidence of ongoing lot conformity testing alongside historical type approval documentation.

Lot conformity procedures evaluate quality control metrics across active manufacturing runs. Inspection engineers draw random cell samples from every production lot destined for international shipment, running non-destructive dimensional scans, open-circuit voltage checks, internal resistance measurements, and weight distribution analysis to detect process drift.

Discrepancies in internal impedance across a production lot signal manufacturing variances that degrade safety limits. An increase in internal resistance elevates heat generation during high-rate discharge cycles, increasing thermal runaway vulnerability. Regulatory auditors analyze statistical batch variance data to verify that shipped lots match certified baseline models.

Thermal Runaway and Mechanical Stress Boundaries

Extreme mechanical stress testing proves cell casing integrity under direct physical collision hazards. The crush test applies a compressive force of 13 kilonewtons using a hydraulic ram equipped with flat or hemispherical actuators. Force continues until cell voltage drops by one hundred millivolts, applied pressure reaches the maximum force setpoint, or the cell casing deforms by ten percent of its initial dimension.

Passing mechanical crush requirements requires zero casing explosion and zero active flame propagation. Mechanical shock testing subjects fully secured cells to half-sine shock pulses achieving peak accelerations of 150 gn for six milliseconds ~ three shock impacts per mutually perpendicular axis to ensure internal cathode leads, anode tabs, and insulative spacers resist mechanical detachment.

Vibration testing subjects samples to simple harmonic motion with a logarithmic frequency sweep between 7 Hertz and 200 Hertz across three hours per axis. The total sweep covers 12 cycles per axis under peak acceleration levels reaching 8 gn. Cells must maintain structural integrity, retain internal voltage within 99 percent of pre-test levels, and exhibit zero physical fluid leakage across cell seal boundaries.

Historical factory audit reports from previous years do not replace current batch test summaries. Compliance regulations recognize no administrative equivalence between historical design certifications and current shipment testing files.

Paperwork

Document administration forms the primary barrier between cell arrival at customs ports and container release. Port inspectors verify that safety paperwork originates from accredited organizations, carries current dates, and aligns with physical shipping crate labels. The import safety dossier must present an uninterrupted chain of technical evidence linking the raw chemical inventory to the finished physical cell model.

A complete safety dossier functions as an integrated technical ledger. Every document corroborates the physical metrics, safety ratings, and handling precautions stated across adjoining shipping filings. Missing cross-references between safety data sheets and physical dangerous goods declarations halt port logistics operations.

Safety Data Sheet Composition Standards

Safety Data Sheets must comply with standard sixteen-section formatting laid down under Globally Harmonized System guidelines. Customs inspection personnel focus their evaluation on Section 1, Section 3, Section 9, and Section 14 during import dossier review. Missing or ambiguous chemical ingredient disclosures trigger regulatory red flags under toxic substance controls.

Section 1 states the exact chemical trade name, internal manufacturer product identifiers, recommended applications, and emergency contact numbers capable of providing immediate technical advice twenty-four hours a day. Section 3 discloses chemical composition, specifying precise CAS numbers, chemical weight percentage ranges, and classification hazards for cathode active materials, anode materials, organic electrolyte solvents, and lithium salts. The disclosure explicitly states lithium hexafluorophosphate content alongside transition metal concentrations including cobalt, nickel, and manganese.

Failure to state the true watt-hour rating on dangerous goods transport documents voids cargo transit insurance coverage under standard haulage contracts.

Section 9 specifies physical and chemical properties, detailing appearance, odor, physical state, flash point, pH balance, melting point, and initial boiling point. Section 14 supplies detailed transport information, identifying assigned UN numbers, official proper shipping descriptions, transport hazard classes, packing groups, and environmental hazard warnings. Discrepancies between Section 14 transport declarations and accompanying hazardous shipping forms lead to immediate cargo detention.

Dangerous Goods Declaration Precision

The Dangerous Goods Declaration forms a legally binding contractual document signed by the shipper of record. The document certifies that the shipment was prepared, packed, marked, and labeled in full compliance with applicable dangerous goods transportation regulations. Customs agencies review declarations to enforce international freight safety standards.

Declarations for rechargeable cell shipments must state proper shipping name UN 3480, Lithium Ion Batteries, assigned Class 9 hazardous goods. The declaration specifies the total net quantity of cells, total gross package mass, and assigned packing instruction numbers under IATA or IMDG freight manuals. Every package entry details the exact quantity and specification of outer UN-approved specification boxes used during transport.

Signatures on dangerous goods declarations must belong to individuals holding active, certified hazardous materials packing qualifications. Customs authorities inspect training records to verify signer credentials when high-risk shipments undergo full documentation audits. Invalid or expired signer certifications invalidate shipping documentation, forcing re-inspection and re-declaration by authorized third-party logistics agents.

Dossier Compilation Sequence

Importers assemble cell safety dossiers using a structured sequence to ensure documentation completeness prior to port arrival.

1. Obtain current, fully executed UN 38.3 test summaries directly from certified testing laboratories for every individual cell model.
2. Secure compliant 16-section Safety Data Sheets printed in the official language of the importing country displaying current chemical inventory metrics.
3. Collect ISO 17025 laboratory accreditation certificates validating that testing facilities possessed authorized scope for cell safety standards at the time testing occurred.
4. Verify commercial shipping invoices, ensuring accurate disclosures of cell quantities, net chemical weights, nominal capacities, and individual watt-hour ratings.
5. Compile cell batch quality inspection sheets displaying factory open-circuit voltage scans, internal resistance distribution figures, and physical dimension checks for the shipped lot.
6. Generate signed dangerous goods shipping declarations matching exact container manifest entries, packaging specification codes, and proper shipping names.
7. Submit the completed safety dossier into the electronic customs portal at least five business days prior to cargo vessel port berth.

Standard supply contracts include mandatory compliance clauses requiring cell suppliers to furnish fully authenticated safety dossiers within forty-eight hours of purchase order issuance. Missing dossier delivery clauses allow buyers to withhold final letter-of-credit balance disbursements until border clearance is granted.

Stamp

Document verification relies heavily on official certification stamps, accreditation marks, and lab seal credentials printed on cell test reports. Customs agencies do not treat all testing certificates equally. Documentation issued by non-accredited facilities or unverified internal factory labs undergoes intensive scrutiny and frequent administrative rejection.

Accreditation bodies evaluate test laboratories to confirm technical competence, equipment calibration rigor, and staff operational qualifications. Import regulatory authorities maintain public registries of authorized accreditation schemes to verify the legitimacy of testing marks stamped onto compliance filings.

ILAC Mutual Recognition Arrangements

The International Laboratory Accreditation Cooperation operates a global Mutual Recognition Arrangement that allows customs authorities to accept test certificates across international borders. Laboratories holding accreditation from an ILAC-MRA signatory body produce test reports that carry international legal standing. Prominent signatory bodies include the American Association for Laboratory Accreditation in the United States, the China National Accreditation Service for Conformity Assessment in China, and DAkkS in Germany.

Customs officials audit test summaries by searching for official ILAC-MRA combination marks alongside national accreditation seals. The test report must print the laboratory’s unique accreditation registration number directly underneath the accreditation body logo. Missing registration numbers indicate unverified report claims, prompting port officials to reject document validity.

Reports bearing simple internal factory quality stamps without third-party accreditation marks trigger mandatory customs quarantine. Importers must demonstrate that internal factory facilities operated under formal ISO/IEC 17025 accreditation programs at the time test samples underwent evaluation. Unaccredited testing requires complete re-testing at domestic certified laboratories at significant expense.

Does Third Party Testing Satisfy Customs Audit Regimes?

Third-party testing conducted by certified independent laboratories provides substantial evidence of design compliance during customs reviews. Independent reports remove commercial bias, proving that cell samples met mandatory safety limits under uncompromised laboratory protocols. Major import jurisdictions prioritize reports issued by established third-party safety certification organizations.

An ISO 17025 laboratory accreditation certificate guarantees technical competence only when the specific cell standard appears in the scope attachment.

Customs audit frameworks evaluate third-party test reports for scope alignment, sample traceability, and report freshness. A valid third-party report must state the exact physical, chemical, and electrical specifications of the cell model submitted for evaluation. If physical dimensions, cathode materials, or separator thicknesses change on active production lines, historical third-party reports become invalid for current import filings.

Importers cannot rely solely on off-the-shelf third-party certificates supplied by cell traders or brokers. Customs authorities demand documented evidence connecting the specific physical batch numbers inside the cargo container to the original test report sample lot. Missing batch connection documentation invalidates third-party certification protections during detailed customs audits.

Laboratory Scope and ISO 17025 Auditing

ISO/IEC 17025 specifies general requirements for the competence, impartiality, and consistent operation of testing and calibration laboratories. Customs auditors scrutinize a testing laboratory’s formal Scope of Accreditation attachment to verify that specific battery standards appear under accredited testing capabilities. A laboratory accredited for general electronic safety testing may lack accredited authority for UN 38.3 or IEC 62133-2 battery destructive testing.

Verification protocols involve querying accreditation body online directories to examine scope schedules. The scope document lists specific test methods, equipment ranges, and measurement uncertainty bounds the laboratory is certified to perform. If UN 38.3 standard T.4 mechanical shock testing does not appear on the laboratory scope schedule, the resulting test summary fails customs audit reviews.

Customs clearance officers evaluate laboratory certificate validity dates to ensure active accreditation status during testing execution. Expired accreditation schedules invalidate test reports, forcing importers to seek retrospective validation or secondary testing approval. Importers verify laboratory scope attachments prior to placing international cell purchase orders.

What specific evidentiary standard will border authorities adopt when solid-state cell architectures with novel metallic anode structures fall outside existing UN 38.3 test method descriptions?

Transit

Transportation regulations dictate the physical conditions under which lithium cells travel across global logistics networks. Dangerous goods packaging standards protect shipments against mechanical shocks, thermal drops, atmospheric pressure shifts, and short-circuit hazards during air, ocean, and highway haulage. Safety dossiers must demonstrate strict adherence to packaging instructions assigned to specific transport modes.

Air transport authorities enforce strict safety directives due to the severe risks thermal runaway events present to aircraft integrity. Maritime and highway carriers enforce parallel modal requirements to prevent cargo fires within dense container holds or enclosed trailers. Packaging specifications define outer carton strength, internal padding insulation, and individual cell isolation methods.

IATA Packing Instruction 965 Requirements

The International Air Transport Association dangerous goods regulations set rigid provisions for shipping secondary lithium-ion cells by air. Packing Instruction 965 applies strictly to standalone loose cell shipments classified under UN 3480. Loose cells are forbidden from carriage on passenger aircraft and must travel exclusively on dedicated cargo freighters.

Packaging under Section IA requires UN specification boxes tested to Packing Group II performance standards. Outer cartons must display official UN specification codes stamped directly onto the box, indicating box style, material type, gross weight limits, and manufacturing origin. Inner packaging must completely enclose each individual cell using non-conductive dividers, blister packs, or insulative plastic sleeves to prevent cell-to-cell contact and terminal short-circuiting.

State of Charge Limits at Freight Handover

Air transport regulations enforce a mandatory maximum State of Charge threshold for secondary lithium-ion cells shipped as standalone cargo. Section IA and Section IB shipments under PI 965 must not exceed 30 percent state of charge at the time of handover to the air carrier. Lower state of charge levels significantly reduce chemical energy density, suppressing internal thermal runaway propagation potential during catastrophic cell failure events.

Importers include formal State of Charge Compliance Declarations inside their dangerous goods import safety files. Cell manufacturers test open-circuit voltage across production lot samples immediately prior to packaging, converting voltage metrics to equivalent capacity state percentage values based on cell chemistry curves. For standard lithium iron phosphate cells, open-circuit voltage at 30 percent state of charge sits near 3.20 volts per cell, while nickel manganese cobalt variants sit near 3.60 volts per cell.

Air cargo terminal acceptance agents perform random open-circuit voltage checks using calibrated digital multimeters to verify compliance declarations. If sample testing reveals state of charge levels exceeding 30 percent, air carriers reject the cargo, blacklisting the shipper from future air express bookings. The importer faces costly return shipping charges or compulsory port-side discharge testing to draw down cell capacity levels.

Maritime and Road Carriage Regulations

Maritime transport under the International Maritime Dangerous Goods Code governs bulk ocean container shipping under UN 3480 standards. Special Provision 188 offers partial regulatory relief for loose cells possessing watt-hour ratings not exceeding 20 Watt-hours. Packages meeting Special Provision 188 dimensions bypass full Class 9 dangerous goods manifest filings while retaining mandatory 1.2-meter drop test packaging resilience and explicit dangerous goods outer box marking requirements.

Road and rail transit across Europe operates under the Agreement concerning the International Carriage of Dangerous Goods by Road. ADR provisions specify vehicle safety equipment, driver hazard training credentials, and dangerous goods transport document requirements. Drivers transporting full container loads of lithium cells must hold valid ADR vocational training certificates covering Class 9 hazard management.

Container transport documents must record total net lithium content and gross battery weights to satisfy road transport load thresholds. Exceeding tunnel restriction codes or vehicle weight limits without proper hazardous material routing permits triggers heavy traffic enforcement penalties and immediate vehicle impoundment at highway weigh stations.

Customs officers hold cargo indefinitely when the cell manufacturer name listed on dangerous goods declarations differs from the legal entity printed on accompanying UN 38.3 test summaries.

Proper dangerous goods packaging requires every cell terminal to remain fully insulated against contact with conductive surfaces throughout ocean transit.

Exposure

Legal and financial liability concentrates heavily on the designated Importer of Record during cross-border cell shipments. Customs authorities enforce regulatory compliance through civil monetary penalties, administrative import revocations, and direct legal asset seizures against non-compliant importing entities. Understanding commercial exposure mechanisms allows purchasing organizations to allocate regulatory risks through structured contractual agreements.

The Importer of Record assumes ultimate legal liability for the safety, tariff accuracy, and statutory compliance of imported cell cargoes. Overseas cell vendors operating outside domestic legal jurisdictions remain largely immune to local customs enforcement actions. Contract structures and regulatory frameworks establish clear boundaries of financial risk during cell sourcing operations.

Importer of Record Legal Responsibilities

Customs laws define the Importer of Record as the legal entity responsible for making entry declarations, filing accurate safety dossiers, and paying applicable import duties. The designated importer must maintain all customs records and technical compliance documentation for a minimum of five years following cargo release. Customs authorities conduct retrospective audits, reviewing historical shipments to identify systemic documentation omissions or tariff misclassifications.

If a customs audit reveals invalid safety documentation, the Importer of Record faces financial penalties under national customs enforcement statutes. Penalties scale based on culpability, ranging from gross negligence fines to civil fraud assessments reaching double the domestic value of the imported merchandise. In severe cases involving intentional safety document forgery, criminal prosecution targets corporate officers signing fraudulent customs entry forms.

Importers remain legally liable even when relying on third-party customs brokers or freight forwarders to clear shipments. Broker errors in declaring cell watt-hour capacities or chemical compositions generate administrative liabilities that land directly on the importing firm. Sourcing practices audit freight broker entries against physical safety files to prevent administrative filing mismatches.

European Union Battery Regulation Mandates

The European Union Battery Regulation (EU) 2023/1542 introduces comprehensive sustainability, safety, and traceability obligations for all cells placed onto the European market. Importers bringing cells into EU member states assume explicit manufacturer-equivalent responsibilities under extended producer responsibility frameworks. Regulation 2023/1542 mandates digital battery passports, recycled content disclosures, and stringent supply chain due diligence verifications.

Battery passport requirements enforce digital traceability for industrial and EV cells possessing capacities exceeding 2 kilowatt-hours. The passport registers detailed technical data, cell chemistry details, recycled cobalt, nickel, and lithium percentages, and carbon footprint disclosures directly into a centralized European database accessible via physical QR codes. Customs agencies enforce market entry bans on cell shipments lacking validated digital passport structures.

Due diligence provisions require importers to audit supply chains for environmental social responsibility, human rights compliance, and raw material sourcing ethics. Importers establish internal verification systems to audit cobalt, nickel, lithium, and graphite mining sources. Failure to present verified supply chain due diligence files during customs entry audits prevents cell cargo release into EU domestic markets.

Commercial Clause Structures and Financial Risk

Commercial sourcing contracts mitigate import exposure by establishing precise risk-transfer milestones between cell buyers and foreign sellers. Standardized Incoterms define the exact physical location where financial risk, shipping costs, and dangerous goods import responsibilities transfer from exporter to importer. Sourcing organizations avoid purchasing cells under Delivered Duty Paid terms without retaining direct control over customs safety dossier submissions.

Delivered Duty Paid terms place customs clearance duties onto foreign sellers who frequently utilize low-cost clearance brokers unfamiliar with specific battery safety rules. Improper broker filings risk cargo seizures that trap buyer capital inside customs impound yards. Contracting under Free Carrier or Free on Board terms gives buyers direct control over dangerous goods declarations, customs safety dossier filings, and qualified customs broker selection.

Calculating landed cost impacts requires factoring potential regulatory delays, inspection fees, and compliance filing expenses into baseline cell unit pricing models. The following financial worked example demonstrates the commercial cost impact of customs documentation holds on a typical import shipment of 50,000 secondary lithium-ion cells imported for industrial pack assembly.

Assume a baseline cell FOB purchase price of $3.50 per cell across 50,000 units, yielding a base shipment value of $175,000. Standard ocean freight, insurance, and terminal handling add $12,000. Tariff entry under HS Code 8507.60.00 carries a 3.4 percent duty rate, generating a baseline duty liability of $6,358.

Total projected landed cost prior to customs delay sits at $193,358, or $3.867 per cell.

A missing UN 38.3 test summary triggers a level-two customs audit hold at the port terminal. The container sits in port storage while the importer secures authenticated test documentation from an accredited laboratory in the exporting country, requiring 18 business days to resolve.

Port demurrage fees accrue at $350 per day for days 1 through 5, escalating to $550 per day for days 6 through 18, generating $8,900 in demurrage costs. Customs administrative hold fees add $1,200. Third-party testing verification and expedited document legalisation fees total $4,500.

Extended financing charges on $175,000 committed capital across 18 days at an 8.5 percent annual interest rate add $733. Total non-compliance operational penalties reach $15,333.

The revised landed cost increases to $208,691, shifting the effective cost per cell from $3.867 to $4.174. This represents an 7.94 percent increase in total landed component expense stemming entirely from documentation omissions. Supply contracts often include liquidated damages clauses requiring sellers to reimburse buyers for all demurrage, administrative hold fees, and testing expenses arising from deficient seller-provided safety files.

Contractual risk-shifting clauses specify that cell acceptance remains conditional upon successful port customs release and domestic laboratory lot verification testing. If imported cell samples fail secondary screening checks, contracts empower buyers to reject the entire batch, forcing the seller to repatriate non-compliant cargo at their own expense.