1. Introduction

Hydrogen blending refers to the controlled injection of hydrogen into an existing natural-gas network so that the resulting gas mixture can be transported through pipelines and supplied to consumers. The principal regulatory question is how much hydrogen, expressed as a percentage of the gas mixture, may legally and safely be introduced into a particular transmission or distribution system.

There is no universally applicable hydrogen-blending percentage. The permissible percentage depends upon:

pipeline material and design;

operating pressure;

compressors and valves;

meters and regulators;

gas-quality requirements;

connected appliances and industrial equipment;

leakage and embrittlement risks;

combustion characteristics;

applicable safety standards;

authorization from the relevant regulator; and

whether the network is a transmission, distribution, or dedicated hydrogen system.

This distinction is particularly important in India because the regulatory framework is still developing. PNGRB's recent material indicates that Indian projects are being conducted at different percentages—such as 2%, 5% and, in one pilot, 8%—rather than under a single nationwide statutory blending ceiling. (PNGRB)

2. Meaning of a Hydrogen Blending Percentage

A hydrogen blending percentage normally refers to the volume fraction (v/v) of hydrogen in the hydrogen-natural-gas mixture.

For example:

2% H₂ = approximately 2 volumes of hydrogen for every 100 volumes of blended gas.

5% H₂ = approximately 5 volumes of hydrogen per 100 volumes.

10% H₂ = approximately 10 volumes per 100 volumes.

20% H₂ = approximately 20 volumes per 100 volumes.

The percentage should not be confused with the percentage of energy supplied by hydrogen. Because hydrogen has substantially lower volumetric energy density than natural gas, a 20% volume blend does not mean that hydrogen supplies 20% of the mixture's energy.

This creates an important regulatory issue concerning metering, calorific value, billing and consumer protection.

3. Why Regulatory Limits Are Necessary

Hydrogen differs materially from conventional natural gas.

A. Lower volumetric energy density

A larger volume of hydrogen is required to deliver the same energy as natural gas. Consequently, blending changes the energy content of the gas supplied to consumers.

B. Wider flammability range

Hydrogen has different combustion and ignition characteristics from methane. Regulators therefore have to examine burners, appliances, ventilation and emergency procedures.

C. Leakage

Hydrogen molecules are extremely small and can behave differently from methane in leakage scenarios. HSE research has specifically examined release and dispersion behaviour from gas-network components when hydrogen or hydrogen blends are transported. (HSE)

D. Material compatibility

Hydrogen can raise concerns concerning material degradation and, under appropriate conditions, hydrogen embrittlement. Pipeline steels, valves, seals, compressors and other components therefore require compatibility assessment.

E. Gas-quality requirements

Increasing hydrogen concentration can affect Wobbe Index, calorific value and other gas-quality parameters. Thus, the legally permissible percentage may be constrained indirectly by gas-quality legislation even where there is no hydrogen-specific numerical ceiling.

4. India: Regulatory Position

4.1 PNGRB framework

The Petroleum and Natural Gas Regulatory Board (PNGRB) is the principal statutory regulator for relevant activities involving natural-gas transmission and city-gas-distribution networks.

The PNGRB Act, 2006 provides the institutional framework for authorization, regulation and technical/safety requirements relating to natural-gas pipelines and CGD networks.

However, India presently does not have one comprehensive statutory provision saying, for example, "hydrogen may constitute a maximum of X% in every natural-gas pipeline."

A recent PNGRB hydrogen roadmap identifies this regulatory gap. It states that, as of 2025, India did not have comprehensive hydrogen-specific regulation covering pipelines, distribution networks, safety devices, metering systems and end-use appliances, and identifies the absence of permissible blending ratios by material class as one of the gaps. (PNGRB)

Therefore, the Indian position should be understood as a project-specific and regulatory-approval-based model, rather than a universal percentage rule.

5. Indian Pilot Percentages

PNGRB's published material demonstrates the developing approach.

Indore

Aavantika Gas conducted hydrogen blending in its MDPE PNG network. The blending level was reported at 5% v/v. (PNGRB)

NTPC Kawas, Gujarat

Gujarat Gas conducted a pilot initially at 5% v/v and subsequently increased the blending percentage to 8% v/v in the MDPE PNG distribution network. (PNGRB)

Jorhat, Assam

PNGRB approved a project involving blending of up to 2% v/v hydrogen into an MDPE network serving domestic consumers. (PNGRB)

Ahmedabad

Adani Total Gas has conducted a pilot involving hydrogen blending up to 5% in an MDPE network. (PNGRB)

Gorakhpur

PNGRB approved a Torrent Gas project involving 2% hydrogen blending in the CGD network. The project covers domestic PNG, CNG and commercial/industrial consumers. (PNGRB)

These figures demonstrate an important legal principle: a pilot approval at 2%, 5% or 8% should not automatically be treated as a nationwide statutory maximum or entitlement.

6. Transmission Versus Distribution Limits

The distinction between transmission and distribution networks is legally significant.

Transmission

Transmission pipelines normally operate at substantially higher pressures and may involve:

high-strength steel;

large compressors;

high-pressure valves;

sophisticated metering;

cross-border or interstate connections; and

large industrial customers.

Consequently, a percentage considered technically manageable in an MDPE distribution network cannot automatically be transferred to a high-pressure transmission pipeline.

PNGRB's research specifically distinguishes blending limits for transmission pipelines, distribution systems, compressors, city-gate stations and meters. (PNGRB)

Distribution

Distribution networks may involve:

MDPE pipelines;

domestic appliances;

commercial boilers;

industrial burners;

CNG facilities.

The regulatory assessment therefore has to consider not only pipeline integrity but also the compatibility of downstream appliances.

7. United Kingdom: An Important Comparative Example

The UK provides a particularly useful illustration of how hydrogen percentage regulation can evolve.

Historically, the Gas Safety (Management) Regulations 1996 restricted hydrogen content in the GB gas network to approximately 0.1% by volume. The UK Hydrogen Strategy explained that deployment above this level required evidence and HSE approval. (GOV.UK)

This did not mean that 0.1% was a scientifically universal safe limit. Rather, it was the regulatory limit under the applicable gas-safety framework.

8. Movement Toward 20% in UK Distribution Networks

Following trials and regulatory work, the UK Government took a strategic policy decision in 2023 supporting the possibility of up to 20% hydrogen by volume in GB gas distribution networks, subject to the necessary safety assessment and implementation framework. (GOV.UK)

The important legal point is that:

20% is not simply an automatic permission to inject hydrogen into every UK gas network.

The policy was expressly conditional upon evidence, safety assessment and enabling regulatory arrangements. (GOV.UK)

The UK Government has also investigated 2%, 5% and 20% blending levels for the National Transmission System. (GOV.UK)

9. European Approach

Europe illustrates why a single universal percentage is difficult.

An EU hydrogen policy analysis identified different national approaches. Examples reported for transmission systems included approximately:

The precise legal status differs between jurisdictions, and some countries regulate through gas-quality specifications rather than a single hydrogen-specific percentage. (European Hydrogen Observatory)

This demonstrates that "the legal hydrogen blending limit" is jurisdiction-specific.

10. United States: No Universal PHMSA Percentage Ceiling

The United States presents a different model.

The Pipeline and Hazardous Materials Safety Administration (PHMSA) has expressly stated that it does not use a particular hydrogen blending ratio to determine whether the federal pipeline-safety regime applies.

PHMSA has authority over transportation of gas—including hydrogen/natural-gas mixtures—in any ratio when the mixture falls within the relevant statutory/regulatory definition of gas. (PHMSA)

Therefore:

Regulatory jurisdiction ≠ permission to use any percentage.

A pipeline operator remains subject to applicable pipeline-safety requirements even where the law does not establish a universal hydrogen-percentage ceiling.

11. Case Law: PNGRB v. Indraprastha Gas Ltd.

Petroleum & Natural Gas Regulatory Board v. Indraprastha Gas Ltd. (2015)

The Supreme Court considered the statutory powers of PNGRB concerning the regulation of natural-gas distribution activities.

The case is important because it examined the limits of PNGRB's statutory regulatory authority, including questions concerning pricing and network-related regulation. (Indian Kanoon)

Relevance to hydrogen blending

Although the case did not decide a hydrogen-blending percentage, its significance is foundational:

A regulator's authority must be traceable to its enabling statute.

For hydrogen blending, this means that PNGRB cannot simply create a nationwide hydrogen percentage restriction—or permission—without an appropriate statutory and regulatory basis.

Hydrogen blending therefore has to be integrated into the existing statutory framework through valid regulations, technical standards, approvals and, where necessary, legislative amendments.

12. Adani Gas Ltd. v. Union of India

In litigation concerning authorization of CGD networks, the courts examined the statutory role of PNGRB and the authorization requirements governing natural-gas distribution networks.

The case illustrates the principle that operation of a gas network requires compliance with the statutory authorization framework and that state-level permissions cannot necessarily substitute for authorization under the PNGRB regime. (Indian Kanoon)

Hydrogen relevance

Suppose an entity has an authorized natural-gas network and wishes to introduce hydrogen.

The existence of authorization to operate the natural-gas network does not necessarily answer the separate technical and safety question of whether hydrogen blending is permitted.

The regulator can therefore require:

technical assessment;

material compatibility analysis;

gas-quality analysis;

metering assessment;

appliance compatibility;

emergency procedures;

monitoring; and

specific project approval.

13. GAIL (India) Ltd. v. PNGRB

In litigation involving PNGRB regulations, the Delhi High Court considered challenges concerning the Board's regulation-making authority under the PNGRB Act. (Indian Kanoon)

This line of authority is relevant to hydrogen regulation because percentage limits are likely to be implemented through delegated legislation, technical standards and regulatory directions.

The legal validity of a hydrogen blending limit will therefore depend upon:

statutory authorization;

consistency with the parent legislation;

proper regulatory procedure;

technical justification; and

proportionality between the safety objective and the restriction imposed.

14. Gas Transportation Cases and Network Regulation

Indian gas-network jurisprudence also establishes that PNGRB possesses substantial regulatory responsibilities concerning common carriers, contract carriers and natural-gas transportation.

For example, litigation concerning Reliance Gas Transportation examined PNGRB's authority concerning transportation tariffs and regulation of common-carrier pipelines. (Indian Kanoon)

Although not a hydrogen case, such decisions provide the institutional foundation for understanding how a future hydrogen-blending framework could operate.

15. Legal Test for Determining the Permissible Percentage

A legally defensible hydrogen-blending percentage should ideally satisfy five tests.

Test 1 — Statutory authority

The regulator must have legal authority to establish or approve the limit.

Test 2 — Technical safety

The percentage must be supported by evidence concerning:

pipeline integrity;

embrittlement;

leakage;

compressors;

valves;

meters;

regulators;

pressure;

combustion;

appliances.

Test 3 — Gas quality

The resulting mixture must satisfy applicable gas-quality requirements.

Test 4 — Consumer protection

The regulator must consider:

calorific value;

billing;

appliance compatibility;

supply continuity;

safety of domestic consumers.

Test 5 — Monitoring and enforcement

The regulator should have mechanisms for:

continuous concentration monitoring;

emergency shutdown;

leakage detection;

reporting;

incident investigation;

penalties for unauthorized blending.

16. Percentage Should Not Be the Only Regulatory Variable

A sophisticated hydrogen-blending regulation should avoid treating percentage as the sole safety parameter.

For example:

5% hydrogen in one network may present a different risk profile from 5% hydrogen in another network.

Relevant variables include:

Risk=f(H2 concentration, pressure, material, temperature, equipment, appliances, operating conditions)Risk=f(H_2\ concentration,\ pressure,\ material,\ temperature,\ equipment,\ appliances,\ operating\ conditions)

Thus, the same nominal hydrogen percentage may produce different regulatory consequences depending on the physical characteristics of the network.

17. Legal Classification of Different Blending Levels

A future Indian regulatory framework could potentially distinguish:

0–2%

Low-level blending subject to standardized technical requirements and monitoring.

2–5%

Intermediate blending requiring more extensive network and appliance compatibility assessment.

5–10%

Higher blending requiring detailed engineering assessment, equipment certification and regulator approval.

10–20%

High-level blending potentially requiring substantial modifications to equipment and gas-quality/billing rules.

Above 20%

Potentially requiring a fundamentally different regulatory model, including dedicated hydrogen infrastructure or extensive conversion of downstream equipment.

These categories are analytical rather than current Indian statutory limits. They should not be presented as existing legal thresholds.

18. Transmission-Level Blending: Special Legal Concerns

Transmission-level blending presents additional problems.

A transmission network may connect several jurisdictions and multiple classes of consumers. If one operator introduces hydrogen, downstream operators may receive gas containing a concentration they have not accepted.

This creates questions concerning:

contractual gas specifications;

cross-border trade;

interoperability;

common-carrier obligations;

liability;

measurement;

balancing;

quality disputes.

European policy analysis has specifically considered the problem of different national blending thresholds at cross-border points. (EUR-Lex)

19. Billing and Consumer Protection

Hydrogen blending can change the calorific value of delivered gas.

Therefore, regulators must decide whether consumers are charged:

per cubic metre;

according to energy content;

according to calorific value;

or under another methodology.

The UK transmission consultation recognizes that billing rules could practically constrain the percentage of hydrogen that can be blended while maintaining existing calorific-value requirements. (GOV.UK)

This demonstrates an important principle:

A technically possible blending percentage may still be legally or commercially impractical because of billing and gas-quality regulation.

20. Regulatory Approval Versus Technical Standard

It is useful to distinguish three separate concepts:

1. Statutory limit
A legally binding maximum percentage established by legislation or regulation.

2. Technical standard
A technical requirement specifying what equipment or network characteristics are acceptable.

3. Project-specific authorization
Permission for a particular operator or pilot project to use a particular hydrogen concentration.

Confusing these three categories can lead to incorrect conclusions about the law.

For example, India's 5% or 8% pilot projects demonstrate what has been approved or tested in particular circumstances; they do not automatically establish a national 5% or 8% statutory ceiling. (PNGRB)

21. Principle of Precaution

Hydrogen blending also raises a precautionary regulatory issue.

Where scientific evidence is incomplete, regulators may legitimately require:

controlled pilots;

limited geographic areas;

concentration ceilings;

continuous monitoring;

emergency response plans;

appliance testing;

staged increases.

The UK experience illustrates this incremental approach: trials and evidence gathering preceded policy movement toward potentially higher blending levels. (GOV.UK)

22. India's Emerging Legal Model

India appears to be moving toward a framework based on pilot projects + technical standards + PNGRB approval + development of hydrogen-specific regulations.

PNGRB has indicated that it is working toward amendments and standards capable of accommodating hydrogen infrastructure. (PNGRB)

Its hydrogen roadmap also identifies areas requiring regulatory development, including:

hydrogen-specific pipeline standards;

material compatibility;

leak detection;

hydrogen-ready meters;

emergency isolation;

safety cases;

gas-quality standards. (PNGRB)

23. Important Case-Law Principle

There is presently a relatively limited body of reported judicial decisions dealing directly with the legality of a hydrogen blending percentage.

Consequently, Indian legal analysis must draw upon broader natural-gas and energy-regulation jurisprudence.

The principal lessons are:

24. Conclusion

Hydrogen blending percentage regulation is not simply a question of selecting 2%, 5%, 10% or 20%. It is a multidimensional regulatory question involving pipeline integrity, gas quality, consumer appliances, metering, safety, authorization and market arrangements.

The international position demonstrates substantial variation. The UK historically operated under a 0.1% regulatory limit but has developed policy supporting potential distribution-network blending of up to 20%, subject to safety and implementation requirements. (GOV.UK) The United States does not use a universal hydrogen-percentage threshold to determine PHMSA jurisdiction. (PHMSA) European countries similarly employ different approaches. (European Hydrogen Observatory)

In India, the more accurate legal position is that there is no single nationwide statutory hydrogen-blending percentage applicable to all natural-gas transmission and CGD networks. Instead, PNGRB-approved projects have operated or been approved at different levels, including 2%, 5% and 8%, while India develops a more comprehensive hydrogen regulatory framework. (PNGRB)

The most important legal principle emerging from the Indian PNGRB cases is that regulatory intervention must remain connected to statutory authority and prescribed regulatory procedures. PNGRB v. Indraprastha Gas Ltd. and the subsequent CGD authorization cases provide the broader jurisprudential foundation, even though they do not themselves establish a hydrogen percentage. (Indian Kanoon)

Accordingly, the future Indian regime is likely to require a risk-based, network-specific and evidence-based hydrogen concentration framework, rather than a single percentage applicable to every pipeline.